CGLOBALS(3) | Common Library Functions | CGLOBALS(3) |
NAME¶
Cglobals - LCG thread-specific global variables interfaceSYNOPSIS¶
#include <Cglobals.h> void Cglobals_init(int (*getspec) (int *key,
void **addr),
int (*setspec) (int *key, void
*addr),
int (*getTid) (void)
);
int Cglobals_get(int *key, void **addr, size_t
size);
void Cglobals_getTid(int *Tid);
int C__serrno();
int C__rfio_errno();
int C__Copterr();
int C__Coptind();
int C__Coptopt();
int C__Coptreset();
char *C__Coptarg();
int C__h_errno();
DESCRIPTION¶
Cglobals is the interface where are defined all necessary functions that always return a thread-specific value of global variables. Each package of LCG that needs to externalize thread-specific global variables contains in its header, if compiled with threads turned on (e.g. the default), a set of:an extern definition to a function contained in
Cglobals
a #define macro that replaces all occurences of any global variable that
needs to be thread-specific to this Cglobal's function.
In order to satisfy packages not compiled with threads turned on, or that do not
initialize LCG Thread Interface's Cthread, any such global
variable is also explicitly defined in Cglobals.
For example, taking the global error variable serrno, Cglobals
source code contains:
an explicit definition of this variable serrno
an explicit definition, with source code, of a function C_serrno() that
does only the following:
The following description of Cglobals_init function is explaining
internals of Cglobals and Cthread. In theory no LCG application
need to call Cglobals_init, you can skip if you want the following
paragraphs, and concentrate only on the other functions descriptions.
Cglobals_init is bundled to work with the LCG Thread Interface's
Cthread. That is, any implicit or explicit call to Cthread
always makes sure that Cglobals_init is called, with three arguments
that are:
if Cglobals_init was not (successfully) called,
return the address of the global variable serrno
else return the address of a thread-safe specific memory, instanciated at the
first call to this function, that holds the content of the current instance of
the thread-specific value of serrno
a getspec function address that, given a static
key address, returns the address of a Thread-Specific memory into
addr content. This uses an internal structure inside Cthread,
allocated on the heap, that is associated bijectively to key address.
Cthread always explicitly allocates such internal structure to any
key address if it is unknown at the moment of the call to
getspec.
In such a case it will return a NULL value into addr , and it will be the
responsability of Cglobals to allocate memory on the heap and to say to
Cthread that this newly allocated memory is the one to associate with
key address, using setspec.
If the internal structure in Cthread associated bijectively to key
yet exists, getspec only returns what it knows about the
thread-specific memory associated with it, which is a void * member
inside the same internal structure mentionned above.
a setspec function address that, given the key address and the
addr value, previously instanciated with a getspec call, and
possibly allocated on the heap by Cglobals if necessary, will
internally explicitly call the Operating System Thread-Specific functions that
will put the value of address as something thread-specific, bijectively
associated to another member of the internal structure of Cthread,
itself bijective to key.
a getTid function address that returns an unique integer identifier
associated with any thread.
Cglobals_get returns in addr content the address of a
thread-specific memory, e.g. thread-safe, that is bijectively associated with
the address of a *static*, e.g. constant, address key , that is
automatically created and filled with zeros if necessary, up to size
bytes.
EXAMPLE¶
Any application can create its own instance of thread-specific global variable using Cglobals. You need only to use Cglobals_get. Here is how to proceed./* * The following shows how to define and use a thread-specific * integer, my_var, inside your package */ #include <stdlib.h> #include <stdio.h> #include <Cglobals.h> /* Get Cglobals_get prototype */ static int my_key = -1; /* Our static key, integer, init value -1 */ #define my_var (*C__my_var()) static int my_var_static; /* If Cglobals_get error in order not to crash */ int *C__my_var() { int *var; /* Call Cglobals_get */ Cglobals_get(&my_key, (void **) &var, sizeof(int) ); /* If error, var will be NULL */ if (var == NULL) { fprintf(stderr,"Cglobals_get error0); return(&my_var_static); } return(var); } int main() { fprintf(stdout, "Current my_var value is: %d0, my_var); fprintf(stdout, "Set my_var value to: %d0, 12); my_var = 12; fprintf(stdout, "Current my_var value is: %d0, my_var); return(0); }
The following example is the source of the test suite for Cglobals_get(): #include <Cthread_api.h> #include <stdlib.h> #include <stdio.h> #include <Cglobals.h> /* Get Cglobals_get prototype */ #include <serrno.h> static int my_key = -1; /* Our static key, integer, init value -1 */ #define my_var (*C__my_var()) static int my_var_static; /* If Cglobals_get error in order not to crash */ void *doit _PROTO((void *)); int doit_v = 0; #define NTHREAD 100 int *C__my_var() { int *var; /* Call Cglobals_get */ switch (Cglobals_get(&my_key, (void **) &var, sizeof(int) )) { case -1: fprintf(stderr,"[%d] Cglobals_get error0, Cthread_self()); break; case 0: fprintf(stderr,"[%d] Cglobals_get OK0, Cthread_self()); break; case 1: fprintf(stderr,"[%d] Cglobals_get OK and first call0, Cthread_self()); break; default: fprintf(stderr,"[%d] Cglobals_get unknown return code0, Cthread_self()); break; } /* If error, var will be NULL */ if (var == NULL) { fprintf(stderr,"[%d] Cglobals_get error : RETURN static ADDRESS!!!!!!!!!!!!0, Cthread_self()); return(&my_var_static); } return(var); } int main() { int i; fprintf(stdout, "[%d] ---> Before any Cthread call0, -1); fprintf(stdout, "[%d] Current my_var value is: %d0, -1, my_var); fprintf(stdout, "[%d] Set my_var value to: %d0, -1, 12); my_var = 12; fprintf(stdout, "[%d] Current my_var value is: %d0, -1, my_var); fprintf(stdout, "[%d] Testing consistency0, -1); if (my_var != 12) { fprintf(stdout, "[%d] Cglobals_get worked ok0, -1); exit(1); } sleep(1); for (i = 0; i < NTHREAD; i++) { Cthread_create(&doit, &doit_v); doit_v++; } fprintf(stdout, "[%d] ---> After all Cthread_create calls0, -1); fprintf(stdout, "[%d] Current my_var value is: %d0, -1, my_var); fprintf(stdout, "[%d] Set my_var value to: %d0, -1, NTHREAD * 10000 + 12); my_var = NTHREAD * 10000 + 12; fprintf(stdout, "[%d] Current my_var value is: %d0, -1, my_var); fprintf(stdout, "[%d] Testing consistency0, -1); if (my_var != (NTHREAD * 10000 + 12)) { fprintf(stdout, "[%d] Cglobals_get worked ok0, -1); exit(1); } sleep(1); exit(0); } void *doit(arg) void *arg; { int Tid; int doit = * (int *) arg; Cglobals_getTid(&Tid); my_var = (Tid + 1) * 100 + 12; fprintf(stdout, "[%d] my_var value is: %d (should be %d)0, Cthread_self(), my_var, (Tid + 1) * 100 + 12); fprintf(stdout, "[%d] second call -- my_var value is: %d (should be %d)0, Cthread_self(), my_var, (Tid + 1) * 100 + 12); fprintf(stdout, "[%d] Testing consistency0, Cthread_self()); if (my_var != ((Tid + 1) * 100 + 12)) { fprintf(stdout, "[%d] !!!!!!!!! ERROR !!!!!!!!!0, Cthread_self()); exit(1); } else { fprintf(stdout, "[%d] Cglobals_get worked ok0, Cthread_self()); } return(0); }
SEE ALSO¶
Cthread(3), serrno(3), Cgetopt(3)AUTHOR¶
LCG Grid Deployment Team$Date: 2010-04-05 09:51:26 +0200 (Mon, 05 Apr 2010) $ | LCG |