NAME¶
IO::AIO - Asynchronous Input/Output
SYNOPSIS¶
use IO::AIO;
aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
my $fh = shift
or die "/etc/passwd: $!";
...
};
aio_unlink "/tmp/file", sub { };
aio_read $fh, 30000, 1024, $buffer, 0, sub {
$_[0] > 0 or die "read error: $!";
};
# version 2+ has request and group objects
use IO::AIO 2;
aioreq_pri 4; # give next request a very high priority
my $req = aio_unlink "/tmp/file", sub { };
$req->cancel; # cancel request if still in queue
my $grp = aio_group sub { print "all stats done\n" };
add $grp aio_stat "..." for ...;
DESCRIPTION¶
This module implements asynchronous I/O using whatever means your operating
system supports. It is implemented as an interface to "libeio"
(<
http://software.schmorp.de/pkg/libeio.html>).
Asynchronous means that operations that can normally block your program (e.g.
reading from disk) will be done asynchronously: the operation will still
block, but you can do something else in the meantime. This is extremely useful
for programs that need to stay interactive even when doing heavy I/O (GUI
programs, high performance network servers etc.), but can also be used to
easily do operations in parallel that are normally done sequentially, e.g.
stat'ing many files, which is much faster on a RAID volume or over NFS when
you do a number of stat operations concurrently.
While most of this works on all types of file descriptors (for example sockets),
using these functions on file descriptors that support nonblocking operation
(again, sockets, pipes etc.) is very inefficient. Use an event loop for that
(such as the EV module): IO::AIO will naturally fit into such an event loop
itself.
In this version, a number of threads are started that execute your requests and
signal their completion. You don't need thread support in perl, and the
threads created by this module will not be visible to perl. In the future,
this module might make use of the native aio functions available on many
operating systems. However, they are often not well-supported or restricted
(GNU/Linux doesn't allow them on normal files currently, for example), and
they would only support aio_read and aio_write, so the remaining functionality
would have to be implemented using threads anyway.
Although the module will work in the presence of other (Perl-) threads, it is
currently not reentrant in any way, so use appropriate locking yourself,
always call "poll_cb" from within the same thread, or never call
"poll_cb" (or other "aio_" functions) recursively.
EXAMPLE¶
This is a simple example that uses the EV module and loads
/etc/passwd
asynchronously:
use EV;
use IO::AIO;
# register the IO::AIO callback with EV
my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
# queue the request to open /etc/passwd
aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
my $fh = shift
or die "error while opening: $!";
# stat'ing filehandles is generally non-blocking
my $size = -s $fh;
# queue a request to read the file
my $contents;
aio_read $fh, 0, $size, $contents, 0, sub {
$_[0] == $size
or die "short read: $!";
close $fh;
# file contents now in $contents
print $contents;
# exit event loop and program
EV::unloop;
};
};
# possibly queue up other requests, or open GUI windows,
# check for sockets etc. etc.
# process events as long as there are some:
EV::loop;
REQUEST ANATOMY AND LIFETIME¶
Every "aio_*" function creates a request. which is a C data structure
not directly visible to Perl.
If called in non-void context, every request function returns a Perl object
representing the request. In void context, nothing is returned, which saves a
bit of memory.
The perl object is a fairly standard ref-to-hash object. The hash contents are
not used by IO::AIO so you are free to store anything you like in it.
During their existance, aio requests travel through the following states, in
order:
- ready
- Immediately after a request is created it is put into the ready state,
waiting for a thread to execute it.
- execute
- A thread has accepted the request for processing and is currently
executing it (e.g. blocking in read).
- pending
- The request has been executed and is waiting for result processing.
While request submission and execution is fully asynchronous, result
processing is not and relies on the perl interpreter calling
"poll_cb" (or another function with the same effect).
- result
- The request results are processed synchronously by "poll_cb".
The "poll_cb" function will process all outstanding aio requests
by calling their callbacks, freeing memory associated with them and
managing any groups they are contained in.
- done
- Request has reached the end of its lifetime and holds no resources anymore
(except possibly for the Perl object, but its connection to the actual aio
request is severed and calling its methods will either do nothing or
result in a runtime error).
FUNCTIONS¶
QUICK OVERVIEW¶
This section simply lists the prototypes most of the functions for quick
reference. See the following sections for function-by-function documentation.
aio_wd $pathname, $callback->($wd)
aio_open $pathname, $flags, $mode, $callback->($fh)
aio_close $fh, $callback->($status)
aio_seek $fh,$offset,$whence, $callback->($offs)
aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
aio_readahead $fh,$offset,$length, $callback->($retval)
aio_stat $fh_or_path, $callback->($status)
aio_lstat $fh, $callback->($status)
aio_statvfs $fh_or_path, $callback->($statvfs)
aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
aio_chown $fh_or_path, $uid, $gid, $callback->($status)
aio_chmod $fh_or_path, $mode, $callback->($status)
aio_truncate $fh_or_path, $offset, $callback->($status)
aio_allocate $fh, $mode, $offset, $len, $callback->($status)
aio_fiemap $fh, $start, $length, $flags, $count, $cb->(\@extents)
aio_unlink $pathname, $callback->($status)
aio_mknod $pathname, $mode, $dev, $callback->($status)
aio_link $srcpath, $dstpath, $callback->($status)
aio_symlink $srcpath, $dstpath, $callback->($status)
aio_readlink $pathname, $callback->($link)
aio_realpath $pathname, $callback->($link)
aio_rename $srcpath, $dstpath, $callback->($status)
aio_mkdir $pathname, $mode, $callback->($status)
aio_rmdir $pathname, $callback->($status)
aio_readdir $pathname, $callback->($entries)
aio_readdirx $pathname, $flags, $callback->($entries, $flags)
IO::AIO::READDIR_DENTS IO::AIO::READDIR_DIRS_FIRST
IO::AIO::READDIR_STAT_ORDER IO::AIO::READDIR_FOUND_UNKNOWN
aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
aio_load $pathname, $data, $callback->($status)
aio_copy $srcpath, $dstpath, $callback->($status)
aio_move $srcpath, $dstpath, $callback->($status)
aio_rmtree $pathname, $callback->($status)
aio_sync $callback->($status)
aio_syncfs $fh, $callback->($status)
aio_fsync $fh, $callback->($status)
aio_fdatasync $fh, $callback->($status)
aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
aio_pathsync $pathname, $callback->($status)
aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
aio_mlockall $flags, $callback->($status)
aio_group $callback->(...)
aio_nop $callback->()
$prev_pri = aioreq_pri [$pri]
aioreq_nice $pri_adjust
IO::AIO::poll_wait
IO::AIO::poll_cb
IO::AIO::poll
IO::AIO::flush
IO::AIO::max_poll_reqs $nreqs
IO::AIO::max_poll_time $seconds
IO::AIO::min_parallel $nthreads
IO::AIO::max_parallel $nthreads
IO::AIO::max_idle $nthreads
IO::AIO::idle_timeout $seconds
IO::AIO::max_outstanding $maxreqs
IO::AIO::nreqs
IO::AIO::nready
IO::AIO::npending
IO::AIO::sendfile $ofh, $ifh, $offset, $count
IO::AIO::fadvise $fh, $offset, $len, $advice
IO::AIO::mmap $scalar, $length, $prot, $flags[, $fh[, $offset]]
IO::AIO::munmap $scalar
IO::AIO::madvise $scalar, $offset, $length, $advice
IO::AIO::mprotect $scalar, $offset, $length, $protect
IO::AIO::munlock $scalar, $offset = 0, $length = undef
IO::AIO::munlockall
API NOTES¶
All the "aio_*" calls are more or less thin wrappers around the
syscall with the same name (sans "aio_"). The arguments are similar
or identical, and they all accept an additional (and optional) $callback
argument which must be a code reference. This code reference will be called
after the syscall has been executed in an asynchronous fashion. The results of
the request will be passed as arguments to the callback (and, if an error
occured, in $!) - for most requests the syscall return code (e.g. most
syscalls return "-1" on error, unlike perl, which usually delivers
"false").
Some requests (such as "aio_readdir") pass the actual results and
communicate failures by passing "undef".
All functions expecting a filehandle keep a copy of the filehandle internally
until the request has finished.
All functions return request objects of type IO::AIO::REQ that allow further
manipulation of those requests while they are in-flight.
The pathnames you pass to these routines
should be absolute. The reason
for this is that at the time the request is being executed, the current
working directory could have changed. Alternatively, you can make sure that
you never change the current working directory anywhere in the program and
then use relative paths. You can also take advantage of IO::AIOs working
directory abstraction, that lets you specify paths relative to some
previously-opened "working directory object" - see the description
of the "IO::AIO::WD" class later in this document.
To encode pathnames as octets, either make sure you either: a) always pass in
filenames you got from outside (command line, readdir etc.) without tinkering,
b) are in your native filesystem encoding, c) use the Encode module and encode
your pathnames to the locale (or other) encoding in effect in the user
environment, d) use Glib::filename_from_unicode on unicode filenames or e) use
something else to ensure your scalar has the correct contents.
This works, btw. independent of the internal UTF-8 bit, which IO::AIO handles
correctly whether it is set or not.
AIO REQUEST FUNCTIONS¶
- $prev_pri = aioreq_pri [$pri]
- Returns the priority value that would be used for the next request and, if
$pri is given, sets the priority for the next aio request.
The default priority is 0, the minimum and maximum priorities are
"-4" and 4, respectively. Requests with higher priority will be
serviced first.
The priority will be reset to 0 after each call to one of the
"aio_*" functions.
Example: open a file with low priority, then read something from it with
higher priority so the read request is serviced before other low priority
open requests (potentially spamming the cache):
aioreq_pri -3;
aio_open ..., sub {
return unless $_[0];
aioreq_pri -2;
aio_read $_[0], ..., sub {
...
};
};
- aioreq_nice $pri_adjust
- Similar to "aioreq_pri", but subtracts the given value from the
current priority, so the effect is cumulative.
- aio_open $pathname, $flags, $mode, $callback->($fh)
- Asynchronously open or create a file and call the callback with a newly
created filehandle for the file (or "undef" in case of an
error).
The pathname passed to "aio_open" must be absolute. See API NOTES,
above, for an explanation.
The $flags argument is a bitmask. See the "Fcntl" module for a
list. They are the same as used by "sysopen".
Likewise, $mode specifies the mode of the newly created file, if it didn't
exist and "O_CREAT" has been given, just like perl's
"sysopen", except that it is mandatory (i.e. use 0 if you don't
create new files, and 0666 or 0777 if you do). Note that the $mode will be
modified by the umask in effect then the request is being executed, so
better never change the umask.
Example:
aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
if ($_[0]) {
print "open successful, fh is $_[0]\n";
...
} else {
die "open failed: $!\n";
}
};
In addition to all the common open modes/flags ("O_RDONLY",
"O_WRONLY", "O_RDWR", "O_CREAT",
"O_TRUNC", "O_EXCL" and "O_APPEND"), the
following POSIX and non-POSIX constants are available (missing ones on
your system are, as usual, 0):
"O_ASYNC", "O_DIRECT", "O_NOATIME",
"O_CLOEXEC", "O_NOCTTY", "O_NOFOLLOW",
"O_NONBLOCK", "O_EXEC", "O_SEARCH",
"O_DIRECTORY", "O_DSYNC", "O_RSYNC",
"O_SYNC" and "O_TTY_INIT".
- aio_close $fh, $callback->($status)
- Asynchronously close a file and call the callback with the result code.
Unfortunately, you can't do this to perl. Perl insists very strongly
on closing the file descriptor associated with the filehandle itself.
Therefore, "aio_close" will not close the filehandle - instead it
will use dup2 to overwrite the file descriptor with the write-end of a
pipe (the pipe fd will be created on demand and will be cached).
Or in other words: the file descriptor will be closed, but it will not be
free for reuse until the perl filehandle is closed.
- aio_seek $fh, $offset, $whence, $callback->($offs)
- Seeks the filehandle to the new $offset, similarly to perl's
"sysseek". The $whence can use the traditional values (0 for
"IO::AIO::SEEK_SET", 1 for "IO::AIO::SEEK_CUR" or 2
for "IO::AIO::SEEK_END").
The resulting absolute offset will be passed to the callback, or
"-1" in case of an error.
In theory, the $whence constants could be different than the corresponding
values from Fcntl, but perl guarantees they are the same, so don't panic.
As a GNU/Linux (and maybe Solaris) extension, also the constants
"IO::AIO::SEEK_DATA" and "IO::AIO::SEEK_HOLE" are
available, if they could be found. No guarantees about suitability for use
in "aio_seek" or Perl's "sysseek" can be made though,
although I would naively assume they "just work".
- aio_read $fh,$offset,$length, $data,$dataoffset,
$callback->($retval)
- aio_write $fh,$offset,$length, $data,$dataoffset,
$callback->($retval)
- Reads or writes $length bytes from or to the specified $fh and $offset
into the scalar given by $data and offset $dataoffset and calls the
callback without the actual number of bytes read (or -1 on error, just
like the syscall).
"aio_read" will, like "sysread", shrink or grow the
$data scalar to offset plus the actual number of bytes read.
If $offset is undefined, then the current file descriptor offset will be
used (and updated), otherwise the file descriptor offset will not be
changed by these calls.
If $length is undefined in "aio_write", use the remaining length
of $data.
If $dataoffset is less than zero, it will be counted from the end of $data.
The $data scalar MUST NOT be modified in any way while the request is
outstanding. Modifying it can result in segfaults or World War III (if the
necessary/optional hardware is installed).
Example: Read 15 bytes at offset 7 into scalar $buffer, starting at offset 0
within the scalar:
aio_read $fh, 7, 15, $buffer, 0, sub {
$_[0] > 0 or die "read error: $!";
print "read $_[0] bytes: <$buffer>\n";
};
- aio_sendfile $out_fh, $in_fh, $in_offset, $length,
$callback->($retval)
- Tries to copy $length bytes from $in_fh to $out_fh. It starts reading at
byte offset $in_offset, and starts writing at the current file offset of
$out_fh. Because of that, it is not safe to issue more than one
"aio_sendfile" per $out_fh, as they will interfere with each
other. The same $in_fh works fine though, as this function does not move
or use the file offset of $in_fh.
Please note that "aio_sendfile" can read more bytes from $in_fh
than are written, and there is no way to find out how many more bytes have
been read from "aio_sendfile" alone, as "aio_sendfile"
only provides the number of bytes written to $out_fh. Only if the result
value equals $length one can assume that $length bytes have been read.
Unlike with other "aio_" functions, it makes a lot of sense to use
"aio_sendfile" on non-blocking sockets, as long as one end
(typically the $in_fh) is a file - the file I/O will then be asynchronous,
while the socket I/O will be non-blocking. Note, however, that you can run
into a trap where "aio_sendfile" reads some data with readahead,
then fails to write all data, and when the socket is ready the next time,
the data in the cache is already lost, forcing "aio_sendfile" to
again hit the disk. Explicit "aio_read" + "aio_write"
let's you better control resource usage.
This call tries to make use of a native "sendfile"-like syscall to
provide zero-copy operation. For this to work, $out_fh should refer to a
socket, and $in_fh should refer to an mmap'able file.
If a native sendfile cannot be found or it fails with "ENOSYS",
"EINVAL", "ENOTSUP", "EOPNOTSUPP",
"EAFNOSUPPORT", "EPROTOTYPE" or "ENOTSOCK",
it will be emulated, so you can call "aio_sendfile" on any type
of filehandle regardless of the limitations of the operating system.
As native sendfile syscalls (as practically any non-POSIX interface hacked
together in a hurry to improve benchmark numbers) tend to be rather buggy
on many systems, this implementation tries to work around some known bugs
in Linux and FreeBSD kernels (probably others, too), but that might fail,
so you really really should check the return value of
"aio_sendfile" - fewre bytes than expected might have been
transferred.
- aio_readahead $fh,$offset,$length, $callback->($retval)
- "aio_readahead" populates the page cache with data from a file
so that subsequent reads from that file will not block on disk I/O. The
$offset argument specifies the starting point from which data is to be
read and $length specifies the number of bytes to be read. I/O is
performed in whole pages, so that offset is effectively rounded down to a
page boundary and bytes are read up to the next page boundary greater than
or equal to (off-set+length). "aio_readahead" does not read
beyond the end of the file. The current file offset of the file is left
unchanged.
If that syscall doesn't exist (likely if your OS isn't Linux) it will be
emulated by simply reading the data, which would have a similar
effect.
- aio_stat $fh_or_path, $callback->($status)
- aio_lstat $fh, $callback->($status)
- Works like perl's "stat" or "lstat" in void context.
The callback will be called after the stat and the results will be
available using "stat _" or "-s _" etc...
The pathname passed to "aio_stat" must be absolute. See API NOTES,
above, for an explanation.
Currently, the stats are always 64-bit-stats, i.e. instead of returning an
error when stat'ing a large file, the results will be silently truncated
unless perl itself is compiled with large file support.
To help interpret the mode and dev/rdev stat values, IO::AIO offers the
following constants and functions (if not implemented, the constants will
be 0 and the functions will either "croak" or fall back on
traditional behaviour).
"S_IFMT", "S_IFIFO", "S_IFCHR",
"S_IFBLK", "S_IFLNK", "S_IFREG",
"S_IFDIR", "S_IFWHT", "S_IFSOCK",
"IO::AIO::major $dev_t", "IO::AIO::minor $dev_t",
"IO::AIO::makedev $major, $minor".
Example: Print the length of /etc/passwd:
aio_stat "/etc/passwd", sub {
$_[0] and die "stat failed: $!";
print "size is ", -s _, "\n";
};
- aio_statvfs $fh_or_path, $callback->($statvfs)
- Works like the POSIX "statvfs" or "fstatvfs" syscalls,
depending on whether a file handle or path was passed.
On success, the callback is passed a hash reference with the following
members: "bsize", "frsize", "blocks",
"bfree", "bavail", "files",
"ffree", "favail", "fsid", "flag"
and "namemax". On failure, "undef" is passed.
The following POSIX IO::AIO::ST_* constants are defined:
"ST_RDONLY" and "ST_NOSUID".
The following non-POSIX IO::AIO::ST_* flag masks are defined to their
correct value when available, or to 0 on systems that do not support them:
"ST_NODEV", "ST_NOEXEC", "ST_SYNCHRONOUS",
"ST_MANDLOCK", "ST_WRITE", "ST_APPEND",
"ST_IMMUTABLE", "ST_NOATIME",
"ST_NODIRATIME" and "ST_RELATIME".
Example: stat "/wd" and dump out the data if successful.
aio_statvfs "/wd", sub {
my $f = $_[0]
or die "statvfs: $!";
use Data::Dumper;
say Dumper $f;
};
# result:
{
bsize => 1024,
bfree => 4333064312,
blocks => 10253828096,
files => 2050765568,
flag => 4096,
favail => 2042092649,
bavail => 4333064312,
ffree => 2042092649,
namemax => 255,
frsize => 1024,
fsid => 1810
}
Here is a (likely partial - send me updates!) list of fsid values used by
Linux - it is safe to hardcode these when $^O is "linux":
0x0000adf5 adfs
0x0000adff affs
0x5346414f afs
0x09041934 anon-inode filesystem
0x00000187 autofs
0x42465331 befs
0x1badface bfs
0x42494e4d binfmt_misc
0x9123683e btrfs
0x0027e0eb cgroupfs
0xff534d42 cifs
0x73757245 coda
0x012ff7b7 coh
0x28cd3d45 cramfs
0x453dcd28 cramfs-wend (wrong endianness)
0x64626720 debugfs
0x00001373 devfs
0x00001cd1 devpts
0x0000f15f ecryptfs
0x00414a53 efs
0x0000137d ext
0x0000ef53 ext2/ext3
0x0000ef51 ext2
0x00004006 fat
0x65735546 fuseblk
0x65735543 fusectl
0x0bad1dea futexfs
0x01161970 gfs2
0x47504653 gpfs
0x00004244 hfs
0xf995e849 hpfs
0x958458f6 hugetlbfs
0x2bad1dea inotifyfs
0x00009660 isofs
0x000072b6 jffs2
0x3153464a jfs
0x6b414653 k-afs
0x0bd00bd0 lustre
0x0000137f minix
0x0000138f minix 30 char names
0x00002468 minix v2
0x00002478 minix v2 30 char names
0x00004d5a minix v3
0x19800202 mqueue
0x00004d44 msdos
0x0000564c novell
0x00006969 nfs
0x6e667364 nfsd
0x00003434 nilfs
0x5346544e ntfs
0x00009fa1 openprom
0x7461636F ocfs2
0x00009fa0 proc
0x6165676c pstorefs
0x0000002f qnx4
0x858458f6 ramfs
0x52654973 reiserfs
0x00007275 romfs
0x67596969 rpc_pipefs
0x73636673 securityfs
0xf97cff8c selinux
0x0000517b smb
0x534f434b sockfs
0x73717368 squashfs
0x62656572 sysfs
0x012ff7b6 sysv2
0x012ff7b5 sysv4
0x01021994 tmpfs
0x15013346 udf
0x00011954 ufs
0x54190100 ufs byteswapped
0x00009fa2 usbdevfs
0x01021997 v9fs
0xa501fcf5 vxfs
0xabba1974 xenfs
0x012ff7b4 xenix
0x58465342 xfs
0x012fd16d xia
- aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
- Works like perl's "utime" function (including the special case
of $atime and $mtime being undef). Fractional times are supported if the
underlying syscalls support them.
When called with a pathname, uses utimes(2) if available, otherwise
utime(2). If called on a file descriptor, uses futimes(2) if
available, otherwise returns ENOSYS, so this is not portable.
Examples:
# set atime and mtime to current time (basically touch(1)):
aio_utime "path", undef, undef;
# set atime to current time and mtime to beginning of the epoch:
aio_utime "path", time, undef; # undef==0
- aio_chown $fh_or_path, $uid, $gid, $callback->($status)
- Works like perl's "chown" function, except that
"undef" for either $uid or $gid is being interpreted as "do
not change" (but -1 can also be used).
Examples:
# same as "chown root path" in the shell:
aio_chown "path", 0, -1;
# same as above:
aio_chown "path", 0, undef;
- aio_truncate $fh_or_path, $offset, $callback->($status)
- Works like truncate(2) or ftruncate(2).
- aio_allocate $fh, $mode, $offset, $len, $callback->($status)
- Allocates or freed disk space according to the $mode argument. See the
linux "fallocate" docuemntation for details.
$mode can currently be 0 or "IO::AIO::FALLOC_FL_KEEP_SIZE" to
allocate space, or "IO::AIO::FALLOC_FL_PUNCH_HOLE |
IO::AIO::FALLOC_FL_KEEP_SIZE", to deallocate a file range.
The file system block size used by "fallocate" is presumably the
"f_bsize" returned by "statvfs".
If "fallocate" isn't available or cannot be emulated (currently no
emulation will be attempted), passes "-1" and sets $! to
"ENOSYS".
- aio_chmod $fh_or_path, $mode, $callback->($status)
- Works like perl's "chmod" function.
- aio_unlink $pathname, $callback->($status)
- Asynchronously unlink (delete) a file and call the callback with the
result code.
- aio_mknod $pathname, $mode, $dev, $callback->($status)
- [EXPERIMENTAL]
Asynchronously create a device node (or fifo). See mknod(2).
The only (POSIX-) portable way of calling this function is:
aio_mknod $pathname, IO::AIO::S_IFIFO | $mode, 0, sub { ...
See "aio_stat" for info about some potentially helpful extra
constants and functions.
- aio_link $srcpath, $dstpath, $callback->($status)
- Asynchronously create a new link to the existing object at $srcpath at the
path $dstpath and call the callback with the result code.
- aio_symlink $srcpath, $dstpath, $callback->($status)
- Asynchronously create a new symbolic link to the existing object at
$srcpath at the path $dstpath and call the callback with the result
code.
- aio_readlink $pathname, $callback->($link)
- Asynchronously read the symlink specified by $path and pass it to the
callback. If an error occurs, nothing or undef gets passed to the
callback.
- aio_realpath $pathname, $callback->($path)
- Asynchronously make the path absolute and resolve any symlinks in $path.
The resulting path only consists of directories (same as Cwd::realpath).
This request can be used to get the absolute path of the current working
directory by passing it a path of . (a single dot).
- aio_rename $srcpath, $dstpath, $callback->($status)
- Asynchronously rename the object at $srcpath to $dstpath, just as
rename(2) and call the callback with the result code.
On systems that support the AIO::WD working directory abstraction natively,
the case "[$wd, "."]" as $srcpath is specialcased -
instead of failing, "rename" is called on the absolute path of
$wd.
- aio_mkdir $pathname, $mode, $callback->($status)
- Asynchronously mkdir (create) a directory and call the callback with the
result code. $mode will be modified by the umask at the time the request
is executed, so do not change your umask.
- aio_rmdir $pathname, $callback->($status)
- Asynchronously rmdir (delete) a directory and call the callback with the
result code.
On systems that support the AIO::WD working directory abstraction natively,
the case "[$wd, "."]" is specialcased - instead of
failing, "rmdir" is called on the absolute path of $wd.
- aio_readdir $pathname, $callback->($entries)
- Unlike the POSIX call of the same name, "aio_readdir" reads an
entire directory (i.e. opendir + readdir + closedir). The entries will not
be sorted, and will NOT include the "." and
".." entries.
The callback is passed a single argument which is either "undef"
or an array-ref with the filenames.
- aio_readdirx $pathname, $flags, $callback->($entries, $flags)
- Quite similar to "aio_readdir", but the $flags argument allows
one to tune behaviour and output format. In case of an error, $entries
will be "undef".
The flags are a combination of the following constants, ORed together (the
flags will also be passed to the callback, possibly modified):
- IO::AIO::READDIR_DENTS
- When this flag is off, then the callback gets an arrayref consisting of
names only (as with "aio_readdir"), otherwise it gets an
arrayref with "[$name, $type, $inode]" arrayrefs, each
describing a single directory entry in more detail.
$name is the name of the entry.
$type is one of the "IO::AIO::DT_xxx" constants:
"IO::AIO::DT_UNKNOWN", "IO::AIO::DT_FIFO",
"IO::AIO::DT_CHR", "IO::AIO::DT_DIR",
"IO::AIO::DT_BLK", "IO::AIO::DT_REG",
"IO::AIO::DT_LNK", "IO::AIO::DT_SOCK",
"IO::AIO::DT_WHT".
"IO::AIO::DT_UNKNOWN" means just that: readdir does not know. If
you need to know, you have to run stat yourself. Also, for speed reasons,
the $type scalars are read-only: you can not modify them.
$inode is the inode number (which might not be exact on systems with 64 bit
inode numbers and 32 bit perls). This field has unspecified content on
systems that do not deliver the inode information.
- IO::AIO::READDIR_DIRS_FIRST
- When this flag is set, then the names will be returned in an order where
likely directories come first, in optimal stat order. This is useful when
you need to quickly find directories, or you want to find all directories
while avoiding to stat() each entry.
If the system returns type information in readdir, then this is used to find
directories directly. Otherwise, likely directories are names beginning
with ".", or otherwise names with no dots, of which names with
short names are tried first.
- IO::AIO::READDIR_STAT_ORDER
- When this flag is set, then the names will be returned in an order
suitable for stat()'ing each one. That is, when you plan to
stat() all files in the given directory, then the returned order
will likely be fastest.
If both this flag and "IO::AIO::READDIR_DIRS_FIRST" are specified,
then the likely dirs come first, resulting in a less optimal stat
order.
- IO::AIO::READDIR_FOUND_UNKNOWN
- This flag should not be set when calling "aio_readdirx".
Instead, it is being set by "aio_readdirx", when any of the
$type's found were "IO::AIO::DT_UNKNOWN". The absence of this
flag therefore indicates that all $type's are known, which can be used to
speed up some algorithms.
- aio_load $pathname, $data, $callback->($status)
- This is a composite request that tries to fully load the given file into
memory. Status is the same as with aio_read.
- aio_copy $srcpath, $dstpath, $callback->($status)
- Try to copy the file (directories not supported as either source or
destination) from $srcpath to $dstpath and call the callback with a status
of 0 (ok) or "-1" (error, see $!).
This is a composite request that creates the destination file with mode 0200
and copies the contents of the source file into it using
"aio_sendfile", followed by restoring atime, mtime, access mode
and uid/gid, in that order.
If an error occurs, the partial destination file will be unlinked, if
possible, except when setting atime, mtime, access mode and uid/gid, where
errors are being ignored.
- aio_move $srcpath, $dstpath, $callback->($status)
- Try to move the file (directories not supported as either source or
destination) from $srcpath to $dstpath and call the callback with a status
of 0 (ok) or "-1" (error, see $!).
This is a composite request that tries to rename(2) the file first;
if rename fails with "EXDEV", it copies the file with
"aio_copy" and, if that is successful, unlinks the
$srcpath.
- aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
- Scans a directory (similar to "aio_readdir") but additionally
tries to efficiently separate the entries of directory $path into two sets
of names, directories you can recurse into (directories), and ones you
cannot recurse into (everything else, including symlinks to directories).
"aio_scandir" is a composite request that creates of many sub
requests_ $maxreq specifies the maximum number of outstanding aio requests
that this function generates. If it is "<= 0", then a
suitable default will be chosen (currently 4).
On error, the callback is called without arguments, otherwise it receives
two array-refs with path-relative entry names.
Example:
aio_scandir $dir, 0, sub {
my ($dirs, $nondirs) = @_;
print "real directories: @$dirs\n";
print "everything else: @$nondirs\n";
};
Implementation notes.
The "aio_readdir" cannot be avoided, but "stat()"'ing
every entry can.
If readdir returns file type information, then this is used directly to find
directories.
Otherwise, after reading the directory, the modification time, size etc. of
the directory before and after the readdir is checked, and if they match
(and isn't the current time), the link count will be used to decide how
many entries are directories (if >= 2). Otherwise, no knowledge of the
number of subdirectories will be assumed.
Then entries will be sorted into likely directories a non-initial dot
currently) and likely non-directories (see "aio_readdirx"). Then
every entry plus an appended "/." will be "stat"'ed,
likely directories first, in order of their inode numbers. If that
succeeds, it assumes that the entry is a directory or a symlink to
directory (which will be checked separately). This is often faster than
stat'ing the entry itself because filesystems might detect the type of the
entry without reading the inode data (e.g. ext2fs filetype feature), even
on systems that cannot return the filetype information on readdir.
If the known number of directories (link count - 2) has been reached, the
rest of the entries is assumed to be non-directories.
This only works with certainty on POSIX (= UNIX) filesystems, which
fortunately are the vast majority of filesystems around.
It will also likely work on non-POSIX filesystems with reduced efficiency as
those tend to return 0 or 1 as link counts, which disables the directory
counting heuristic.
- aio_rmtree $pathname, $callback->($status)
- Delete a directory tree starting (and including) $path, return the status
of the final "rmdir" only. This is a composite request that uses
"aio_scandir" to recurse into and rmdir directories, and unlink
everything else.
- aio_sync $callback->($status)
- Asynchronously call sync and call the callback when finished.
- aio_fsync $fh, $callback->($status)
- Asynchronously call fsync on the given filehandle and call the callback
with the fsync result code.
- aio_fdatasync $fh, $callback->($status)
- Asynchronously call fdatasync on the given filehandle and call the
callback with the fdatasync result code.
If this call isn't available because your OS lacks it or it couldn't be
detected, it will be emulated by calling "fsync" instead.
- aio_syncfs $fh, $callback->($status)
- Asynchronously call the syncfs syscall to sync the filesystem associated
to the given filehandle and call the callback with the syncfs result code.
If syncfs is not available, calls sync(), but returns
"-1" and sets errno to "ENOSYS" nevertheless.
- aio_sync_file_range $fh, $offset, $nbytes, $flags,
$callback->($status)
- Sync the data portion of the file specified by $offset and $length to disk
(but NOT the metadata), by calling the Linux-specific sync_file_range
call. If sync_file_range is not available or it returns ENOSYS, then
fdatasync or fsync is being substituted.
$flags can be a combination of
"IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE",
"IO::AIO::SYNC_FILE_RANGE_WRITE" and
"IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER": refer to the
sync_file_range manpage for details.
- aio_pathsync $pathname, $callback->($status)
- This request tries to open, fsync and close the given path. This is a
composite request intended to sync directories after directory operations
(E.g. rename). This might not work on all operating systems or have any
specific effect, but usually it makes sure that directory changes get
written to disc. It works for anything that can be opened for read-only,
not just directories.
Future versions of this function might fall back to other methods when
"fsync" on the directory fails (such as calling
"sync").
Passes 0 when everything went ok, and "-1" on error.
- aio_msync $scalar, $offset = 0, $length = undef, flags = 0,
$callback->($status)
- This is a rather advanced IO::AIO call, which only works on
mmap(2)ed scalars (see the "IO::AIO::mmap" function,
although it also works on data scalars managed by the Sys::Mmap or Mmap
modules, note that the scalar must only be modified in-place while an aio
operation is pending on it).
It calls the "msync" function of your OS, if available, with the
memory area starting at $offset in the string and ending $length bytes
later. If $length is negative, counts from the end, and if $length is
"undef", then it goes till the end of the string. The flags can
be a combination of "IO::AIO::MS_ASYNC",
"IO::AIO::MS_INVALIDATE" and "IO::AIO::MS_SYNC".
- aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0,
$callback->($status)
- This is a rather advanced IO::AIO call, which works best on
mmap(2)ed scalars.
It touches (reads or writes) all memory pages in the specified range inside
the scalar. All caveats and parameters are the same as for
"aio_msync", above, except for flags, which must be either 0
(which reads all pages and ensures they are instantiated) or
"IO::AIO::MT_MODIFY", which modifies the memory pages (by
reading and writing an octet from it, which dirties the page).
- aio_mlock $scalar, $offset = 0, $length = undef,
$callback->($status)
- This is a rather advanced IO::AIO call, which works best on
mmap(2)ed scalars.
It reads in all the pages of the underlying storage into memory (if any) and
locks them, so they are not getting swapped/paged out or removed.
If $length is undefined, then the scalar will be locked till the end.
On systems that do not implement "mlock", this function returns
"-1" and sets errno to "ENOSYS".
Note that the corresponding "munlock" is synchronous and is
documented under "MISCELLANEOUS FUNCTIONS".
Example: open a file, mmap and mlock it - both will be undone when $data
gets destroyed.
open my $fh, "<", $path or die "$path: $!";
my $data;
IO::AIO::mmap $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh;
aio_mlock $data; # mlock in background
- aio_mlockall $flags, $callback->($status)
- Calls the "mlockall" function with the given $flags (a
combination of "IO::AIO::MCL_CURRENT" and
"IO::AIO::MCL_FUTURE").
On systems that do not implement "mlockall", this function returns
"-1" and sets errno to "ENOSYS".
Note that the corresponding "munlockall" is synchronous and is
documented under "MISCELLANEOUS FUNCTIONS".
Example: asynchronously lock all current and future pages into memory.
aio_mlockall IO::AIO::MCL_FUTURE;
- aio_fiemap $fh, $start, $length, $flags, $count, $cb->(\@extents)
- Queries the extents of the given file (by calling the Linux
"FIEMAP" ioctl, see
<http://cvs.schmorp.de/IO-AIO/doc/fiemap.txt> for details). If the
ioctl is not available on your OS, then this request will fail with
"ENOSYS".
$start is the starting offset to query extents for, $length is the size of
the range to query - if it is "undef", then the whole file will
be queried.
$flags is a combination of flags ("IO::AIO::FIEMAP_FLAG_SYNC" or
"IO::AIO::FIEMAP_FLAG_XATTR" -
"IO::AIO::FIEMAP_FLAGS_COMPAT" is also exported), and is
normally 0 or "IO::AIO::FIEMAP_FLAG_SYNC" to query the data
portion.
$count is the maximum number of extent records to return. If it is
"undef", then IO::AIO queries all extents of the range. As a
very special case, if it is 0, then the callback receives the number of
extents instead of the extents themselves (which is unreliable, see
below).
If an error occurs, the callback receives no arguments. The special
"errno" value "IO::AIO::EBADR" is available to test
for flag errors.
Otherwise, the callback receives an array reference with extent structures.
Each extent structure is an array reference itself, with the following
members:
[$logical, $physical, $length, $flags]
Flags is any combination of the following flag values (typically either 0 or
"IO::AIO::FIEMAP_EXTENT_LAST" (1)):
"IO::AIO::FIEMAP_EXTENT_LAST",
"IO::AIO::FIEMAP_EXTENT_UNKNOWN",
"IO::AIO::FIEMAP_EXTENT_DELALLOC",
"IO::AIO::FIEMAP_EXTENT_ENCODED",
"IO::AIO::FIEMAP_EXTENT_DATA_ENCRYPTED",
"IO::AIO::FIEMAP_EXTENT_NOT_ALIGNED",
"IO::AIO::FIEMAP_EXTENT_DATA_INLINE",
"IO::AIO::FIEMAP_EXTENT_DATA_TAIL",
"IO::AIO::FIEMAP_EXTENT_UNWRITTEN",
"IO::AIO::FIEMAP_EXTENT_MERGED" or
"IO::AIO::FIEMAP_EXTENT_SHARED".
At the time of this writing (Linux 3.2), this requets is unreliable unless
$count is "undef", as the kernel has all sorts of bugs
preventing it to return all extents of a range for files with large number
of extents. The code works around all these issues if $count is
undef.
- aio_group $callback->(...)
- This is a very special aio request: Instead of doing something, it is a
container for other aio requests, which is useful if you want to bundle
many requests into a single, composite, request with a definite callback
and the ability to cancel the whole request with its subrequests.
Returns an object of class IO::AIO::GRP. See its documentation below for
more info.
Example:
my $grp = aio_group sub {
print "all stats done\n";
};
add $grp
(aio_stat ...),
(aio_stat ...),
...;
- aio_nop $callback->()
- This is a special request - it does nothing in itself and is only used for
side effects, such as when you want to add a dummy request to a group so
that finishing the requests in the group depends on executing the given
code.
While this request does nothing, it still goes through the execution phase
and still requires a worker thread. Thus, the callback will not be
executed immediately but only after other requests in the queue have
entered their execution phase. This can be used to measure request
latency.
- IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT
EXPORTED*
- Mainly used for debugging and benchmarking, this aio request puts one of
the request workers to sleep for the given time.
While it is theoretically handy to have simple I/O scheduling requests like
sleep and file handle readable/writable, the overhead this creates is
immense (it blocks a thread for a long time) so do not use this function
except to put your application under artificial I/O pressure.
IO::AIO::WD - multiple working directories¶
Your process only has one current working directory, which is used by all
threads. This makes it hard to use relative paths (some other component could
call "chdir" at any time, and it is hard to control when the path
will be used by IO::AIO).
One solution for this is to always use absolute paths. This usually works, but
can be quite slow (the kernel has to walk the whole path on every access), and
can also be a hassle to implement.
Newer POSIX systems have a number of functions (openat, fdopendir, futimensat
and so on) that make it possible to specify working directories per operation.
For portability, and because the clowns who "designed", or shall I
write, perpetrated this new interface were obviously half-drunk, this
abstraction cannot be perfect, though.
IO::AIO allows you to convert directory paths into a so-called IO::AIO::WD
object. This object stores the canonicalised, absolute version of the path,
and on systems that allow it, also a directory file descriptor.
Everywhere where a pathname is accepted by IO::AIO (e.g. in "aio_stat"
or "aio_unlink"), one can specify an array reference with an
IO::AIO::WD object and a pathname instead (or the IO::AIO::WD object alone,
which gets interpreted as "[$wd, "."]"). If the pathname
is absolute, the IO::AIO::WD object is ignored, otherwise the pathname is
resolved relative to that IO::AIO::WD object.
For example, to get a wd object for
/etc and then stat
passwd
inside, you would write:
aio_wd "/etc", sub {
my $etcdir = shift;
# although $etcdir can be undef on error, there is generally no reason
# to check for errors here, as aio_stat will fail with ENOENT
# when $etcdir is undef.
aio_stat [$etcdir, "passwd"], sub {
# yay
};
};
That "aio_wd" is a request and not a normal function shows that
creating an IO::AIO::WD object is itself a potentially blocking operation,
which is why it is done asynchronously.
To stat the directory obtained with "aio_wd" above, one could write
either of the following three request calls:
aio_lstat "/etc" , sub { ... # pathname as normal string
aio_lstat [$wd, "."], sub { ... # "." relative to $wd (i.e. $wd itself)
aio_lstat $wd , sub { ... # shorthand for the previous
As with normal pathnames, IO::AIO keeps a copy of the working directory object
and the pathname string, so you could write the following without causing any
issues due to $path getting reused:
my $path = [$wd, undef];
for my $name (qw(abc def ghi)) {
$path->[1] = $name;
aio_stat $path, sub {
# ...
};
}
There are some caveats: when directories get renamed (or deleted), the pathname
string doesn't change, so will point to the new directory (or nowhere at all),
while the directory fd, if available on the system, will still point to the
original directory. Most functions accepting a pathname will use the directory
fd on newer systems, and the string on older systems. Some functions (such as
realpath) will always rely on the string form of the pathname.
So this functionality is mainly useful to get some protection against
"chdir", to easily get an absolute path out of a relative path for
future reference, and to speed up doing many operations in the same directory
(e.g. when stat'ing all files in a directory).
The following functions implement this working directory abstraction:
- aio_wd $pathname, $callback->($wd)
- Asynchonously canonicalise the given pathname and convert it to an
IO::AIO::WD object representing it. If possible and supported on the
system, also open a directory fd to speed up pathname resolution relative
to this working directory.
If something goes wrong, then "undef" is passwd to the callback
instead of a working directory object and $! is set appropriately. Since
passing "undef" as working directory component of a pathname
fails the request with "ENOENT", there is often no need for
error checking in the "aio_wd" callback, as future requests
using the value will fail in the expected way.
- IO::AIO::CWD
- This is a compiletime constant (object) that represents the process
current working directory.
Specifying this object as working directory object for a pathname is as if
the pathname would be specified directly, without a directory object. For
example, these calls are functionally identical:
aio_stat "somefile", sub { ... };
aio_stat [IO::AIO::CWD, "somefile"], sub { ... };
To recover the path associated with an IO::AIO::WD object, you can use
"aio_realpath":
aio_realpath $wd, sub {
warn "path is $_[0]\n";
};
Currently, "aio_statvfs" always, and "aio_rename" and
"aio_rmdir" sometimes, fall back to using an absolue path.
IO::AIO::REQ CLASS¶
All non-aggregate "aio_*" functions return an object of this class
when called in non-void context.
- cancel $req
- Cancels the request, if possible. Has the effect of skipping execution
when entering the execute state and skipping calling the callback
when entering the the result state, but will leave the request
otherwise untouched (with the exception of readdir). That means that
requests that currently execute will not be stopped and resources held by
the request will not be freed prematurely.
- cb $req $callback->(...)
- Replace (or simply set) the callback registered to the request.
IO::AIO::GRP CLASS¶
This class is a subclass of IO::AIO::REQ, so all its methods apply to objects of
this class, too.
A IO::AIO::GRP object is a special request that can contain multiple other aio
requests.
You create one by calling the "aio_group" constructing function with a
callback that will be called when all contained requests have entered the
"done" state:
my $grp = aio_group sub {
print "all requests are done\n";
};
You add requests by calling the "add" method with one or more
"IO::AIO::REQ" objects:
$grp->add (aio_unlink "...");
add $grp aio_stat "...", sub {
$_[0] or return $grp->result ("error");
# add another request dynamically, if first succeeded
add $grp aio_open "...", sub {
$grp->result ("ok");
};
};
This makes it very easy to create composite requests (see the source of
"aio_move" for an application) that work and feel like simple
requests.
- •
- The IO::AIO::GRP objects will be cleaned up during calls to
"IO::AIO::poll_cb", just like any other request.
- •
- They can be canceled like any other request. Canceling will cancel not
only the request itself, but also all requests it contains.
- •
- They can also can also be added to other IO::AIO::GRP objects.
- •
- You must not add requests to a group from within the group callback (or
any later time).
Their lifetime, simplified, looks like this: when they are empty, they will
finish very quickly. If they contain only requests that are in the
"done" state, they will also finish. Otherwise they will continue to
exist.
That means after creating a group you have some time to add requests (precisely
before the callback has been invoked, which is only done within the
"poll_cb"). And in the callbacks of those requests, you can add
further requests to the group. And only when all those requests have finished
will the the group itself finish.
- add $grp ...
- $grp->add (...)
- Add one or more requests to the group. Any type of IO::AIO::REQ can be
added, including other groups, as long as you do not create circular
dependencies.
Returns all its arguments.
- $grp->cancel_subs
- Cancel all subrequests and clears any feeder, but not the group request
itself. Useful when you queued a lot of events but got a result early.
The group request will finish normally (you cannot add requests to the
group).
- $grp->result (...)
- Set the result value(s) that will be passed to the group callback when all
subrequests have finished and set the groups errno to the current value of
errno (just like calling "errno" without an error number). By
default, no argument will be passed and errno is zero.
- $grp->errno ([$errno])
- Sets the group errno value to $errno, or the current value of errno when
the argument is missing.
Every aio request has an associated errno value that is restored when the
callback is invoked. This method lets you change this value from its
default (0).
Calling "result" will also set errno, so make sure you either set
$! before the call to "result", or call c<errno> after
it.
- feed $grp $callback->($grp)
- Sets a feeder/generator on this group: every group can have an attached
generator that generates requests if idle. The idea behind this is that,
although you could just queue as many requests as you want in a group,
this might starve other requests for a potentially long time. For example,
"aio_scandir" might generate hundreds of thousands of
"aio_stat" requests, delaying any later requests for a long
time.
To avoid this, and allow incremental generation of requests, you can instead
a group and set a feeder on it that generates those requests. The feed
callback will be called whenever there are few enough (see
"limit", below) requests active in the group itself and is
expected to queue more requests.
The feed callback can queue as many requests as it likes (i.e.
"add" does not impose any limits).
If the feed does not queue more requests when called, it will be
automatically removed from the group.
If the feed limit is 0 when this method is called, it will be set to 2
automatically.
Example:
# stat all files in @files, but only ever use four aio requests concurrently:
my $grp = aio_group sub { print "finished\n" };
limit $grp 4;
feed $grp sub {
my $file = pop @files
or return;
add $grp aio_stat $file, sub { ... };
};
- limit $grp $num
- Sets the feeder limit for the group: The feeder will be called whenever
the group contains less than this many requests.
Setting the limit to 0 will pause the feeding process.
The default value for the limit is 0, but note that setting a feeder
automatically bumps it up to 2.
SUPPORT FUNCTIONS¶
EVENT PROCESSING AND EVENT LOOP INTEGRATION
- $fileno = IO::AIO::poll_fileno
- Return the request result pipe file descriptor. This filehandle
must be polled for reading by some mechanism outside this module (e.g. EV,
Glib, select and so on, see below or the SYNOPSIS). If the pipe becomes
readable you have to call "poll_cb" to check the results.
See "poll_cb" for an example.
- IO::AIO::poll_cb
- Process some requests that have reached the result phase (i.e. they have
been executed but the results are not yet reported). You have to call this
"regularly" to finish outstanding requests.
Returns 0 if all events could be processed (or there were no events to
process), or "-1" if it returned earlier for whatever reason.
Returns immediately when no events are outstanding. The amount of events
processed depends on the settings of "IO::AIO::max_poll_req",
"IO::AIO::max_poll_time" and
"IO::AIO::max_outstanding".
If not all requests were processed for whatever reason, the poll file
descriptor will still be ready when "poll_cb" returns, so
normally you don't have to do anything special to have it called later.
Apart from calling "IO::AIO::poll_cb" when the event filehandle
becomes ready, it can be beneficial to call this function from loops which
submit a lot of requests, to make sure the results get processed when they
become available and not just when the loop is finished and the event loop
takes over again. This function returns very fast when there are no
outstanding requests.
Example: Install an Event watcher that automatically calls IO::AIO::poll_cb
with high priority (more examples can be found in the SYNOPSIS section, at
the top of this document):
Event->io (fd => IO::AIO::poll_fileno,
poll => 'r', async => 1,
cb => \&IO::AIO::poll_cb);
- IO::AIO::poll_wait
- Wait until either at least one request is in the result phase or no
requests are outstanding anymore.
This is useful if you want to synchronously wait for some requests to become
ready, without actually handling them.
See "nreqs" for an example.
- IO::AIO::poll
- Waits until some requests have been handled.
Returns the number of requests processed, but is otherwise strictly
equivalent to:
IO::AIO::poll_wait, IO::AIO::poll_cb
- IO::AIO::flush
- Wait till all outstanding AIO requests have been handled.
Strictly equivalent to:
IO::AIO::poll_wait, IO::AIO::poll_cb
while IO::AIO::nreqs;
- IO::AIO::max_poll_reqs $nreqs
- IO::AIO::max_poll_time $seconds
- These set the maximum number of requests (default 0, meaning infinity)
that are being processed by "IO::AIO::poll_cb" in one call,
respectively the maximum amount of time (default 0, meaning infinity)
spent in "IO::AIO::poll_cb" to process requests (more correctly
the mininum amount of time "poll_cb" is allowed to use).
Setting "max_poll_time" to a non-zero value creates an overhead of
one syscall per request processed, which is not normally a problem unless
your callbacks are really really fast or your OS is really really slow (I
am not mentioning Solaris here). Using "max_poll_reqs" incurs no
overhead.
Setting these is useful if you want to ensure some level of interactiveness
when perl is not fast enough to process all requests in time.
For interactive programs, values such as 0.01 to 0.1 should be fine.
Example: Install an Event watcher that automatically calls IO::AIO::poll_cb
with low priority, to ensure that other parts of the program get the CPU
sometimes even under high AIO load.
# try not to spend much more than 0.1s in poll_cb
IO::AIO::max_poll_time 0.1;
# use a low priority so other tasks have priority
Event->io (fd => IO::AIO::poll_fileno,
poll => 'r', nice => 1,
cb => &IO::AIO::poll_cb);
CONTROLLING THE NUMBER OF THREADS
- IO::AIO::min_parallel $nthreads
- Set the minimum number of AIO threads to $nthreads. The current default is
8, which means eight asynchronous operations can execute concurrently at
any one time (the number of outstanding requests, however, is unlimited).
IO::AIO starts threads only on demand, when an AIO request is queued and no
free thread exists. Please note that queueing up a hundred requests can
create demand for a hundred threads, even if it turns out that everything
is in the cache and could have been processed faster by a single thread.
It is recommended to keep the number of threads relatively low, as some
Linux kernel versions will scale negatively with the number of threads
(higher parallelity => MUCH higher latency). With current Linux 2.6
versions, 4-32 threads should be fine.
Under most circumstances you don't need to call this function, as the module
selects a default that is suitable for low to moderate load.
- IO::AIO::max_parallel $nthreads
- Sets the maximum number of AIO threads to $nthreads. If more than the
specified number of threads are currently running, this function kills
them. This function blocks until the limit is reached.
While $nthreads are zero, aio requests get queued but not executed until the
number of threads has been increased again.
This module automatically runs "max_parallel 0" at program end, to
ensure that all threads are killed and that there are no outstanding
requests.
Under normal circumstances you don't need to call this function.
- IO::AIO::max_idle $nthreads
- Limit the number of threads (default: 4) that are allowed to idle (i.e.,
threads that did not get a request to process within the idle timeout
(default: 10 seconds). That means if a thread becomes idle while $nthreads
other threads are also idle, it will free its resources and exit.
This is useful when you allow a large number of threads (e.g. 100 or 1000)
to allow for extremely high load situations, but want to free resources
under normal circumstances (1000 threads can easily consume 30MB of RAM).
The default is probably ok in most situations, especially if thread creation
is fast. If thread creation is very slow on your system you might want to
use larger values.
- IO::AIO::idle_timeout $seconds
- Sets the minimum idle timeout (default 10) after which worker threads are
allowed to exit. SEe "IO::AIO::max_idle".
- IO::AIO::max_outstanding $maxreqs
- Sets the maximum number of outstanding requests to $nreqs. If you do queue
up more than this number of requests, the next call to
"IO::AIO::poll_cb" (and other functions calling
"poll_cb", such as "IO::AIO::flush" or
"IO::AIO::poll") will block until the limit is no longer
exceeded.
In other words, this setting does not enforce a queue limit, but can be used
to make poll functions block if the limit is exceeded.
This is a very bad function to use in interactive programs because it
blocks, and a bad way to reduce concurrency because it is inexact: Better
use an "aio_group" together with a feed callback.
It's main use is in scripts without an event loop - when you want to stat a
lot of files, you can write somehting like this:
IO::AIO::max_outstanding 32;
for my $path (...) {
aio_stat $path , ...;
IO::AIO::poll_cb;
}
IO::AIO::flush;
The call to "poll_cb" inside the loop will normally return
instantly, but as soon as more thna 32 reqeusts are in-flight, it will
block until some requests have been handled. This keeps the loop from
pushing a large number of "aio_stat" requests onto the queue.
The default value for "max_outstanding" is very large, so there is
no practical limit on the number of outstanding requests.
STATISTICAL INFORMATION
- IO::AIO::nreqs
- Returns the number of requests currently in the ready, execute or pending
states (i.e. for which their callback has not been invoked yet).
Example: wait till there are no outstanding requests anymore:
IO::AIO::poll_wait, IO::AIO::poll_cb
while IO::AIO::nreqs;
- IO::AIO::nready
- Returns the number of requests currently in the ready state (not yet
executed).
- IO::AIO::npending
- Returns the number of requests currently in the pending state (executed,
but not yet processed by poll_cb).
MISCELLANEOUS FUNCTIONS
IO::AIO implements some functions that might be useful, but are not
asynchronous.
- IO::AIO::sendfile $ofh, $ifh, $offset, $count
- Calls the "eio_sendfile_sync" function, which is like
"aio_sendfile", but is blocking (this makes most sense if you
know the input data is likely cached already and the output filehandle is
set to non-blocking operations).
Returns the number of bytes copied, or "-1" on error.
- IO::AIO::fadvise $fh, $offset, $len, $advice
- Simply calls the "posix_fadvise" function (see its manpage for
details). The following advice constants are available:
"IO::AIO::FADV_NORMAL", "IO::AIO::FADV_SEQUENTIAL",
"IO::AIO::FADV_RANDOM", "IO::AIO::FADV_NOREUSE",
"IO::AIO::FADV_WILLNEED", "IO::AIO::FADV_DONTNEED".
On systems that do not implement "posix_fadvise", this function
returns ENOSYS, otherwise the return value of
"posix_fadvise".
- IO::AIO::madvise $scalar, $offset, $len, $advice
- Simply calls the "posix_madvise" function (see its manpage for
details). The following advice constants are available:
"IO::AIO::MADV_NORMAL", "IO::AIO::MADV_SEQUENTIAL",
"IO::AIO::MADV_RANDOM", "IO::AIO::MADV_WILLNEED",
"IO::AIO::MADV_DONTNEED".
On systems that do not implement "posix_madvise", this function
returns ENOSYS, otherwise the return value of
"posix_madvise".
- IO::AIO::mprotect $scalar, $offset, $len, $protect
- Simply calls the "mprotect" function on the preferably
AIO::mmap'ed $scalar (see its manpage for details). The following protect
constants are available: "IO::AIO::PROT_NONE",
"IO::AIO::PROT_READ", "IO::AIO::PROT_WRITE",
"IO::AIO::PROT_EXEC".
On systems that do not implement "mprotect", this function returns
ENOSYS, otherwise the return value of "mprotect".
- IO::AIO::mmap $scalar, $length, $prot, $flags, $fh[, $offset]
- Memory-maps a file (or anonymous memory range) and attaches it to the
given $scalar, which will act like a string scalar. Returns true on
success, and false otherwise.
The only operations allowed on the scalar are
"substr"/"vec" that don't change the string length,
and most read-only operations such as copying it or searching it with
regexes and so on.
Anything else is unsafe and will, at best, result in memory leaks.
The memory map associated with the $scalar is automatically removed when the
$scalar is destroyed, or when the "IO::AIO::mmap" or
"IO::AIO::munmap" functions are called.
This calls the "mmap"(2) function internally. See your system's
manual page for details on the $length, $prot and $flags parameters.
The $length must be larger than zero and smaller than the actual filesize.
$prot is a combination of "IO::AIO::PROT_NONE",
"IO::AIO::PROT_EXEC", "IO::AIO::PROT_READ" and/or
"IO::AIO::PROT_WRITE",
$flags can be a combination of "IO::AIO::MAP_SHARED" or
"IO::AIO::MAP_PRIVATE", or a number of system-specific flags
(when not available, the are defined as 0):
"IO::AIO::MAP_ANONYMOUS" (which is set to "MAP_ANON"
if your system only provides this constant),
"IO::AIO::MAP_HUGETLB", "IO::AIO::MAP_LOCKED",
"IO::AIO::MAP_NORESERVE", "IO::AIO::MAP_POPULATE" or
"IO::AIO::MAP_NONBLOCK"
If $fh is "undef", then a file descriptor of "-1" is
passed.
$offset is the offset from the start of the file - it generally must be a
multiple of "IO::AIO::PAGESIZE" and defaults to 0.
Example:
use Digest::MD5;
use IO::AIO;
open my $fh, "<verybigfile"
or die "$!";
IO::AIO::mmap my $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh
or die "verybigfile: $!";
my $fast_md5 = md5 $data;
- IO::AIO::munmap $scalar
- Removes a previous mmap and undefines the $scalar.
- IO::AIO::munlock $scalar, $offset = 0, $length = undef
- Calls the "munlock" function, undoing the effects of a previous
"aio_mlock" call (see its description for details).
- IO::AIO::munlockall
- Calls the "munlockall" function.
On systems that do not implement "munlockall", this function
returns ENOSYS, otherwise the return value of "munlockall".
- IO::AIO::splice $r_fh, $r_off, $w_fh, $w_off, $length, $flags
- Calls the GNU/Linux splice(2) syscall, if available. If $r_off or $w_off
are "undef", then "NULL" is passed for these,
otherwise they should be the file offset.
$r_fh and $w_fh should not refer to the same file, as splice might silently
corrupt the data in this case.
The following symbol flag values are available:
"IO::AIO::SPLICE_F_MOVE",
"IO::AIO::SPLICE_F_NONBLOCK", "IO::AIO::SPLICE_F_MORE"
and "IO::AIO::SPLICE_F_GIFT".
See the splice(2) manpage for details.
- IO::AIO::tee $r_fh, $w_fh, $length, $flags
- Calls the GNU/Linux tee(2) syscall, see it's manpage and the description
for "IO::AIO::splice" above for details.
- $actual_size = IO::AIO::pipesize $r_fh[, $new_size]
- Attempts to query or change the pipe buffer size. Obviously works only on
pipes, and currently works only on GNU/Linux systems, and fails with
"-1"/"ENOSYS" everywhere else. If anybody knows how to
influence pipe buffer size on other systems, drop me a note.
EVENT LOOP INTEGRATION¶
It is recommended to use AnyEvent::AIO to integrate IO::AIO automatically into
many event loops:
# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
use AnyEvent::AIO;
You can also integrate IO::AIO manually into many event loops, here are some
examples of how to do this:
# EV integration
my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
# Event integration
Event->io (fd => IO::AIO::poll_fileno,
poll => 'r',
cb => \&IO::AIO::poll_cb);
# Glib/Gtk2 integration
add_watch Glib::IO IO::AIO::poll_fileno,
in => sub { IO::AIO::poll_cb; 1 };
# Tk integration
Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
readable => \&IO::AIO::poll_cb);
# Danga::Socket integration
Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
\&IO::AIO::poll_cb);
FORK BEHAVIOUR¶
Usage of pthreads in a program changes the semantics of fork considerably.
Specifically, only async-safe functions can be called after fork. Perl doesn't
know about this, so in general, you cannot call fork with defined behaviour in
perl if pthreads are involved. IO::AIO uses pthreads, so this applies, but
many other extensions and (for inexplicable reasons) perl itself often is
linked against pthreads, so this limitation applies to quite a lot of perls.
This module no longer tries to fight your OS, or POSIX. That means IO::AIO only
works in the process that loaded it. Forking is fully supported, but using
IO::AIO in the child is not.
You might get around by not
using IO::AIO before (or after) forking. You
could also try to call the IO::AIO::reinit function in the child:
- IO::AIO::reinit
- Abandons all current requests and I/O threads and simply reinitialises all
data structures. This is not an operation supported by any standards, but
happens to work on GNU/Linux and some newer BSD systems.
The only reasonable use for this function is to call it after forking, if
"IO::AIO" was used in the parent. Calling it while IO::AIO is
active in the process will result in undefined behaviour. Calling it at
any time will also result in any undefined (by POSIX) behaviour.
MEMORY USAGE¶
Per-request usage:
Each aio request uses - depending on your architecture - around 100-200 bytes of
memory. In addition, stat requests need a stat buffer (possibly a few hundred
bytes), readdir requires a result buffer and so on. Perl scalars and other
data passed into aio requests will also be locked and will consume memory till
the request has entered the done state.
This is not awfully much, so queuing lots of requests is not usually a problem.
Per-thread usage:
In the execution phase, some aio requests require more memory for temporary
buffers, and each thread requires a stack and other data structures (usually
around 16k-128k, depending on the OS).
KNOWN BUGS¶
Known bugs will be fixed in the next release.
SEE ALSO¶
AnyEvent::AIO for easy integration into event loops, Coro::AIO for a more
natural syntax.
AUTHOR¶
Marc Lehmann <schmorp@schmorp.de>
http://home.schmorp.de/