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NAME
Cthread - LCG Thread inferface
SYNOPSIS
#include <Cthread_api.h>
int Cthread_create(void *(*startroutine)(void *), void * arg);
int Cthread_create_detached(void *(*startroutine)(void *),void *arg);
int Cthread_join(int cid, int **status);
int Cthread_mutex_lock(void *addr);
int Cthread_mutex_trylock(void *addr);
int Cthread_mutex_timedlock(void *addr, int timeout);
int Cthread_mutex_unlock(void *addr);
int Cthread_mutex_destroy(void *addr);
int Cthread_cond_wait(void *addr);
int Cthread_cond_timedwait(void *addr, int timeout);
int Cthread_cond_signal(void *addr);
int Cthread_cond_broadcast(void *addr);
int Cthread_detach(int cid);
int Cthread_kill(int cid, int signo);
int Cthread_exit(void *status);
int Cthread_self(void);
int Cthread_getspecific(int *global_key, void **addr);
int Cthread_setspecific(int *global_key, void * addr);
DESCRIPTION
Cthread is a common API interface for multithreaded programs, although there is also
support for nonthreaded application, where some of the Cthread functions then becomes
useless.
For non-thread applications see the section NON-THREAD ENVIRONMENT
Any created thread is identified uniquely with a cid, standing for Cthread identifier.
In multithread environment, Cthread is an interface to pthread functions on UNIX, and an
interface to Win32 C-runtime library on Windows/NT.
Cthread_create is creating a thread given its starting point startroutine and its
arguments arg address. The thread is created with the default parameters, e.g. it is a
joinable thread.
Return value is the Cthread identifier cid , greater or equal to zero, or -1 on error.
Cthread_create_detached takes the same arguments as Cthread_create and (tries) to create a
detachable thread, which will then make it act as a daemon. This means that ressources
used by this thread will be freed immediately when it terminates. On the other hand, such
thread cannot be synchronized with other threads using the Cthread_join method.
You have to remind that creating a detachable thread do not work immediately at the
creation step on every thread implementation, in particular in the DCE threads. If the
implementation do not allow this at creation time, then Cthread_create_detached calls
Cthread_create. Please have a look at Cthread_detach section.
Return value is the Cthread identifier cid , greater or equal to zero, or -1 on error.
Cthread_exit makes current thread exiting. If status isn't NULL, it is assumed to point to
an integer whose value if the status that a Cthread_join would received, in case the
thread is joinable. Please note that Cthread_exit is dangerous and non-recommended on
Windows platform.
Return value is 0 on success, or -1 on error.
Cthread_kill sends signo signal number to the thread cid. This affect the status that a
Cthread_join would received, in case the thread to be killed is joinable. Please note that
Cthread_kill is not supported on DCE threads.
Return value is 0 on success, or -1 on error.
Cthread_join suspends the calling thread until the one identified with the Cthread
identifier cid terminates. If the status parameter is not NULL, the status of the
terminating thread cid is stored there. This status is the pointer returned by thread cid
at its end.
Return value is 0 on success, or -1 on error.
Cthread_mutex_lock is an alias for Cthread_mutex_timedlock with a timeout of -1.
Cthread_mutex_trylock is an alias for Cthread_mutex_timedlock with a timeout of 0.
Cthread_mutex_timedlock is acquiring a mutex, creating it if necessary, on the addr
address. The second parameter is the eventual timeout in seconds. If this parameter is <
0, the calling thread is suspended until it is granted access to addr , if it is zero, the
calling thread will try to gain the lock, and if it is greater than zero the calling
thread will wait up to timeout seconds.
Please note that, in Cthread, a creation of a mutex is always associated with a creation
of a conditionnal variable. See Cthread_cond_timedwait and Cthread_cond_broadcast_.
Return value is 0 on success, or -1 on error.
Cthread_mutex_unlock is unlocking the mutex that the calling thread is assumed to have
acquired previously, calling Cthread_mutex_timedlock on the addr address.
Cthread_cond_wait is an alias for Cthread_cond_timedwait with a timeout of -1.
Cthread_cond_timedwait is waiting for a condition variable, which is, by default in
Cthread, broadcasted, associated with a mutex previously created on the addr address.
Calling this function before the creation and the lock of a mutex, with
Cthread_mutex_timedlock is a programming error.
While the thread is waiting on a condition to arise on the addr address, the corresponding
lock is released. It will be acquired as soon as the condition happens. Please note that
the use of condition is subject to normal thread programming rules, e.g. the lock, a loop
on a predicate, a wait inside the loop, and the unlock.
If the timeout parameter, in seconds, is greater than zero, then the function will not
suspend the calling thread more than this limit.
Return value is 0 on success, or -1 on error.
Cthread_cond_signal is an alias for Cthread_cond_broadcast.
Cthread_cond_broadcast restarts threads that are waiting on a condition variable vs. addr
address.
Return value is 0 on success, or -1 on error.
Cthread_detach is detaching the calling thread, identified with cid Cthread identifier.
Whereas the normal thread packages that allow a thread to be detached at the creation
step, see Cthread_create_detached, returns an error if such a detached thread tries to
detach himself again, Cthread_detach will not, because of this different behaviour vs.
different thread implementations: it is not possible everywhere to create a detached
thread immediately, like in DCE threads.
This means that if a user is creating a thread with Cthread_create or
Cthread_create_detached, the created thread will, in any case, be allowed to call
Cthread_detach: if the calling thread is not yet detached, it will be changed so forth,
and if the calling thread is already detached, the return value will be 0.
Return value is 0 on success, or -1 on error.
Cthread_mutex_destroy is removing its corresponding entry in Cthread internal linked list,
freeing all thread associated stuff, like the mutex itself, and the conditionnal variable
(see Cthread_mutex_timedlock).
Return value is 0 on success, or -1 on error.
Cthread_self is returning the Cthread identifier cid of the calling thread.
Return value is the cid (greater or equal to zero) on success, or -1 on error.
Cthread_getspecific is creating and/or getting a thread-specific storage address for every
instance of the global_key address, storing its result in addr location. The first time it
is called, the stored result is NULL, next time it will be the address of the memory the
user would have previously allocated and associated with the key using
Cthread_setspecific.
Return value is 0 on success, or -1 on error.
Cthread_setspecific is associating a memory, starting at addr that he have previously
allocated, with the global_key address. If he tries to do so without calling previously
Cthread_getspecific, then such a call will be done internally.
Return value is 0 on success, or -1 on error.
ERRORS
Beyond the errno value, Cthread is setting the serrno value to generic values that can be:
SECTHREADINIT
LCG Thread interface initialization error
A thread initialisation call failed. In principle, on UNIX this will be a call to
pthread_mutex_init (and possibly pthread_mutexattr_init) that failed, on Windows/NT
this might be a call to CreateMutex.
SECTHREADERR
LCG Thread interface failure in calling your thread library
A thread call to your native system library (like the pthread one on UNIX) failed.
Please note that this is differentiated to the Cthread initialization and can
happen if you are using too much thread keys, for example. This is really a run-
time error only concerning your operating system thread interface. Any other system
call failure, but not a thread one, and not at the initialisation step, will set
serrno to SEINTERNAL
SEOPNOTSUP
Operation not supported
This can be generated only if you compiled Cthread with a -DCTHREAD_PROTO flag that
Cthread do not know about. Check your LCG configuration site.def.
SEINTERNAL
Internal error
You can have more information by compiling the Cthread package with the flag
-DCTHREAD_DEBUG, and catching the printout on your stderr stream. This is any
system call that failed (like malloc()), except those to the thread library (for
which SECTHREADERR or SECTHREADINIT is to be found), or any critical internal run-
time error (such as a non correct value found in some Cthread internal structures).
SETIMEDOUT (routines with a timeout parameter only)
Timed out
You called a routine with a timeout value greater than zero that reached the
maximum number of timeout seconds in waiting state.
EINVAL
Invalid parameters
You called a routine with invalid parameter(s). Please check your code.
EXAMPLES
Here is an example with thread-specific data
#include <Cthread_api.h> /* Cthread include file */
#include <stdio.h> /* For I/O functions and definitions */
#define NTHREADS 5 /* Number of threads */
#define NLOOP 5 /* Number of loops in threads */
static int global_key;
/* Internal Prototypes */
void *mythread(void *);
void testit();
int main() {
int i, n;
for (i=1; i <= NTHREADS; i++) {
if ((n = Cthread_create(&mythread,NULL)) < 0) {
exit(EXIT_FAILURE);
} else {
fprintf(stderr,"[main] --> Created Cthread ID %d\n",n);
}
}
sleep(NTHREADS);
exit(EXIT_SUCCESS);
}
void *mythread(void *arg) {
int i;
/* Call the same routine NLOOP times */
for (i=1; i <= NLOOP; i++) {
testit();
}
return(NULL);
}
void testit() {
char *addr = NULL;
int n;
if ((n = Cthread_detach(Cthread_self())))
exit(EXIT_FAILURE);
if ((n = Cthread_getspecific(&global_key,(void **) &addr)))
exit(EXIT_FAILURE);
if (addr == NULL) {
addr = malloc(100);
fprintf(stderr,"[%d] --> new 0x%x\n",
Cthread_self(),addr);
if (Cthread_setspecific(&global_key,addr))
exit(EXIT_FAILURE);
} else {
fprintf(stderr,"[%d] --> old 0x%x\n",
Cthread_self(),addr);
}
sprintf(addr,"[%d] Print with TSD buffer : Cthread ID=%d\n",
Cthread_self(),Cthread_self());
fprintf(stderr,addr);
return;
}
NON-THREAD ENVIRONMENT
In such an environment, almost all methods becomes no-op, except:
Creation of process(es):
Cthread_create
Cthread_create_detached (equivalent to Cthread_create)
Cthread_join
Use of "Process"-specific variables:
Cthread_getspecific
Cthread_setspecific
For these two last functions, Cthread will garbage itself its eventual list of
"Process"-specific variables. This means that, as in a thread environment, the user
will not have to free memory allocated and registered with a call to
Cthread_setspecific.
SEE ALSO
pthread, DCE, LinuxThreads, Win32
AUTHOR
LCG Grid Deployment Team