NAME¶
FBB::SharedStream - I/O operations on shared memory
SYNOPSIS¶
#include <bobcat/sharedstream>
Linking option:
-lpthread -lbobcat
DESCRIPTION¶
This class combines the features of the
std::istream and
std::ostream classes, operating on shared memory. As with
std::fstream objects, a
seekp or
seekg member call is
required to switch from writing to reading or v.v.
As with
std::fstream objects,
FBB::SharedStream objects do not
keep separate offsets for reading and writeing: the seek-members always refer
to the (single) offset maintained by the
FBB::SharedMemory object to
which the
SharedStream object interfaces.
So, although
tellg and
tellp return identical values,
tellg
should not be called after writing to a
SharedStream object, and
tellp should not be called after reading from a
SharedStream
object, as calling members related to reading (
tellg) after writing
and v.v. put the stream in its fail state.
NAMESPACE¶
FBB
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace
FBB.
INHERITS FROM¶
FBB::SharedStreambuf (private inheritance),
std::istream,
std::ostream,
FBB::SharedEnum__ (cf.
sharedmemory(3bobcat) for a description of
this base class).
SIZEUNIT ENUMERATION¶
The
enum SizeUnit defines the following symbolic constants:
- o
- kB, representing 1024 (2**10) bytes of memory;
- o
- MB, representing 1048576 (2**20 bytes of memory;
- o
- GB, representing 1073741824 (2**30) bytes of memory )
CONSTRUCTORS¶
- o
- SharedStream():
The default constructor defines a stub a SharedStream object that
cannot immediately be used to access shared memory. To use it, its member
open must first be called.
- o
- SharedStream(size_t maxSize, SizeUnit sizeUnit,
std::ios::openmode openMode = std::ios::in | std::ios::out,
size_t access = 0600):
This constructor creates a stream inheriting the facilities of an
std::istream and std::ostream that interfaces to a shared
memory segment having a capacity of at least maxSize * sizeUnit
bytes.
- By default, the shared memory segment is opened for reading and writing.
Different from the open modes used for file streams, creating a shared
memory stream with open modes ios::in | ios::out is OK. In this
case the shared memory segment is created and once information has been
written to the shared memory it can also be read again.
- The shared memory’s access rights are defined by the access
parameter, interpreted as an octal value, using the well-known (
chmod(1)) way to define the access rights for owner, group and
others.
- If construction fails, an FBB::Exception is thrown.
- o
- SharedStream(int id, std::ios::openmode openMode = std::ios::in |
std::ios::out):
This constructor creates a stream inheriting the facilities of an
std::istream and std::ostream that connects to a shared
memory segment having ID id.
- Specifying the ios::trunc flag immediately clears the contents of
the shared memory.
- An FBB::Exception is thrown if construction fails (e.g., no shared
memory segment having ID id exists), Copy and move constructors are
not available.
OVERLOADED OPERATORS¶
- No overloaded move and copy assignment operators are available.
MEMBER FUNCTIONS¶
- All members of std::istream and std::ostream and the
enum values kB, MB, and GB, defined by
FBB::SharedEnum__ are available.
- o
- FBB::SharedCondition attachSharedCondition(std::ios::off_type
offset, std::ios::seekdir origin):
Returns an FBB::SharedCondition(3) object, interfacing to a shared
condition variable located at offset offset (relative to
origin) in the SharedMemory object to which the
SharedStream object interfaces. This member does not alter the
value returned by the stream’s tellg and tellp
members.
- An FBB::Exception is thrown if the FBB::SharedCondition
object could not be constructed.
- o
- FBB::SharedCondition createSharedCondition():
Returns an FBB::SharedCondition(3) object, interfacing to a newly
created shared condition variable which is created at the current offset
of the SharedMemory object to which the SharedStream object
interfaces (or at the first offset of the next physical shared memory data
block, cf. sharedcondition(3bobcat)). Creating a
SharedCondition object does not alter the value returned by the
stream’s tellg and tellp members.
- An FBB::Exception is thrown if the FBB::SharedCondition
object could not be constructed.
- o
- int id() const:
The ID of the shared memory segment is returned.
- o
- void kill():
Without locking the shared memory first, all shared memory is returned to
the operating system. The FBB::SharedStream object is unusable
after returning from kill. Other processes that were using the
shared memory can continue to do so.
- o
- void memInfo(std::ostream &out, char const *end =
"\n"):
Information about the SharedMemory object is inserted into the
provide ostream object. The IDs of the shared segments, their
sizes, the maximum number of shared memory segments, the number of bytes
that can be read from the shared memory, and its actual storage capacity,
etc., are displayed. Following the information about the shared memory,
end is inserted into out.
- o
- void open(size_t maxSize, SizeUnit sizeUnit, std::ios::openmode
openMode = std::ios::in | std::ios::out, size_t access = 0600):
This member creates a shared memory segment having a capacity of at least
maxSize * sizeUnit bytes, and connects the shared memory segment to
the FBB::SharedStream. A matching close member does not
exist and is not required.
- By default, the shared memory segment is opened for reading and writing.
Different from the open modes used for file streams, creating a shared
memory stream with open modes ios::in | ios::out is OK. In this
case the shared memory segment is created and once information has been
written to the shared memory it can also be read again.
- The shared memory’s access rights are defined by the access
parameter, interpreted as an octal value, using the well-known (
chmod(1)) way to define the access rights for owner, group and
others.
- If opening fails, an FBB::Exception is thrown.
- o
- void open(int id, std::ios::openmode openMode = std::ios::in |
std::ios::out):
This member connects the FBB::SharedStream object to a shared memory
segment having ID id. A matching close member does not exist
and is not required. If opening succeeds the shared memory is ready for
use.
- Specifying the ios::trunc flag immediately clears the contents of
the shared memory.
- An FBB::Exception is thrown if opening fails (e.g., no shared
memory segment having ID id exists).
- o
- void remove():
The shared memory is first locked. Next, all shared memory is returned to
the operating system. The FBB::SharedStream object is unusable
after returning from remove. Other processes that were using the
shared memory can continue to do so.
- o
- bool truncate(std::streamsize offset):
If offset is not exceeding the value returned by seekg(0,
std::ios::end), then this latter value is changed to offset
and true is returned. Otherwise false is returned, and the
value returned by seekg is not altered. If the value returned by
tellg exceeded offset, tellg’s return value it
is reduced to offset as well. Subsequent read operations on the
shared memory can only succeed as long as tellg’s return
value hasn’t reached the value offset.
EXAMPLE¶
#include <iostream>
#include <string>
#include <ostream>
#include <istream>
#include <bobcat/exception>
#include <bobcat/sharedstream>
#include <bobcat/sharedcondition>
using namespace std;
using namespace FBB;
int main()
{
SharedStream sharedStream;
int id = -1;
while (true)
{
cout <<
"\n"
" K kill (no lock) existing shared segment\n"
" S show stats of current shared segment\n"
" L <id> Load segment <id>\n"
" C Install a SharedCondition at offset 0\n"
" c create new shared memory (sets id)\n"
// " l lock segment id until key pressed\n"
// " p <x> c put char c at offset x\n"
" q quit\n"
// " r <x> <n> read n chars from offset x\n"
// " w <x> args write all args at offset x\n"
" i insert lines (until empty) at the current "
"offset\n"
" x extract lines (until EOF) from the current "
"offset\n"
" X extract the next line from the current "
"offset\n"
" when nodified via ’N’\n"
" N notify a waiting X\n"
" s <x> seek (abs) offset x\n"
"? ";
char ch;
cin >> ch;
ios::off_type offset;
cout << "Requested: " << ch << ’\n’;
sharedStream.clear();
switch (ch)
{
case ’c’:
{
sharedStream.open(1, SharedStream::kB);
id = sharedStream.id();
cout << "id = " << id << ’\n’;
sharedStream.memInfo(cout);
cout << ’\n’;
}
break;
case ’C’:
{
sharedStream.seekp(0);
SharedCondition cond(sharedStream.createSharedCondition());
sharedStream.seekg(cond.width());
break;
}
case ’K’: // delete segment
{
if (id == -1)
{
cout << "No segment loaded\n";
continue;
}
cout << "Removing segment id = " << id << ’\n’;
if (ch == ’R’)
sharedStream.remove();
else
sharedStream.kill();
id = -1;
}
break;
case ’L’:
cin >> id;
cout << "Loading segment " << id << ’\n’;
sharedStream.open(id);
sharedStream.memInfo(cout);
cout << ’\n’;
break;
case ’S’:
if (id == -1)
{
cout << "No segment loaded\n";
continue;
}
sharedStream.memInfo(cout);
cout << ’\n’;
break;
case ’s’:
{
size_t offset;
if (id == -1)
{
cout << "No segment loaded\n";
continue;
}
cin >> offset;
sharedStream.seekg(offset);
sharedStream.seekp(offset);
cout << "tellg: " << sharedStream.tellg() << ", "
"tellp: " << sharedStream.tellp() << ’\n’;
}
break;
case ’i’:
{
string line;
getline(cin, line);
sharedStream.seekp(0, ios::cur);
while (true)
{
cout << "? ";
if (not getline(cin, line) || line.empty())
break;
sharedStream << line << endl;
cout <<
" tellp: " << sharedStream.tellp() << ’\n’;
}
cout << // " tellg: " << sharedStream.tellg() << ", "
" tellp: " << sharedStream.tellp() << ’\n’;
}
break;
case ’x’:
{
string line;
sharedStream.seekg(0, ios::cur);
while (true)
{
cout << ": ";
if (not getline(sharedStream, line))
break;
cout << line << "\n"
" tellg: " << sharedStream.tellg() << ", "
" tellp: " << sharedStream.tellp() << ’\n’;
}
}
break;
case ’X’:
{
SharedCondition cond(sharedStream.attachSharedCondition(0));
string line;
sharedStream.seekg(cond.width());
cond.lock();
while (true)
{
cond.wait();
cout << ": ";
if (not getline(sharedStream, line))
break;
cout << line << "\n"
" tellg: " << sharedStream.tellg() << ", "
" tellp: " << sharedStream.tellp() << ’\n’;
}
cout << "All done\n";
cond.unlock();
}
break;
case ’N’:
{
string line;
getline(cin, line);
SharedCondition cond(sharedStream.attachSharedCondition(0));
while (true)
{
cout << "’enter’ or ’q’? ";
getline(cin, line);
if (line == "q")
break;
cond.lock();
cond.notify();
cond.unlock();
}
}
break;
case ’p’: // put a char behind the last written
{
if (id == -1)
{
cout << "No segment loaded\n";
continue;
}
cin >> offset >> ch;
if (!cin)
throw Exception() << "cmd specification error";
sharedStream.seekp(offset);
cout << "Segment id = " << id << " at write offset " <<
sharedStream.tellp() << ’\n’;
sharedStream.put(ch);
}
break;
case ’r’: // put a char behind the last written
{
if (id == -1)
{
cout << "No segment loaded\n";
continue;
}
int n;
cin >> offset >> n;
if (!cin)
throw Exception() << "cmd specification error";
char buf[n];
sharedStream.seekg(offset);
cout << "Segment id = " << id << " at offset " <<
sharedStream.tellg() << ", to read " << n << " bytes\n";
n = sharedStream.read(buf, n).gcount();
if (n < 0)
cout << "No data at " << offset << ’\n’;
else
{
cout << "Retrieved " << n << " bytes, containing `";
cout.write(buf, n);
cout << "’\n";
for (auto ch: buf)
cout << static_cast<int>(ch) << ’ ’;
cout << ’\n’;
}
}
break;
case ’w’: // write chars at offset
{
if (id == -1)
{
cout << "No segment loaded\n";
continue;
}
string line;
cin >> offset;
getline(cin, line);
if (!cin)
throw Exception() << "cmd specification error";
streampos pos = sharedStream.seekp(offset).tellp();
cout << "Segment id = " << id << " at offset " <<
pos << ", to write " << line.length() << " bytes\n";
sharedStream.write(line.data(), line.length());
if (!sharedStream)
cout << "No room left to write any bytes\n";
else
cout << "Wrote " << (sharedStream.tellp() - pos) << " bytes\n";
}
break;
case ’q’:
return 0;
default:
cout << "request not implemented: " << ch << ’\n’;
break;
}
}
}
FILES¶
bobcat/sharedstream - defines the class interface
SEE ALSO¶
bobcat(7),
chmod(1),
isharedstream(3bobcat),
osharedstream(3bobcat),
sharedblock(3bobcat),
sharedcondition(3bobcat),
sharedmemory(3bobcat)
sharedmutex(3bobcat),
sharedpos(3bobcat),
sharedsegment(3bobcat),
sharedstreambuf(3bobcat)
BUGS¶
Note that by default exceptions thrown from within a
std::stream object
are caught by the stream object, setting its
ios::failbit flag. To
allow exceptions to leave a stream object, its
exceptions member can be
called, e.g., using:
myStream.exceptions(ios::failbit | ios::badbit | ios::eofbit);
DISTRIBUTION FILES¶
- o
- bobcat_3.23.01-x.dsc: detached signature;
- o
- bobcat_3.23.01-x.tar.gz: source archive;
- o
- bobcat_3.23.01-x_i386.changes: change log;
- o
- libbobcat1_3.23.01-x_*.deb: debian package holding the
libraries;
- o
- libbobcat1-dev_3.23.01-x_*.deb: debian package holding the
libraries, headers and manual pages;
- o
- http://sourceforge.net/projects/bobcat: public archive location;
BOBCAT¶
Bobcat is an acronym of `Brokken’s Own Base Classes And
Templates’.
COPYRIGHT¶
This is free software, distributed under the terms of the GNU General Public
License (GPL).
AUTHOR¶
Frank B. Brokken (
f.b.brokken@rug.nl).