Standard C Library Functions pthread_create(3C)
NAME
pthread_create - create a thread
SYNOPSIS
cc -mt [ flag... ] file... -lpthread [ library... ]
#include
int pthread_create(pthread_t *restrict thread,
const pthread_attr_t *restrict attr,
void *(*start_routine)(void*), void *restrict arg);
DESCRIPTION
The pthread_create() function is used to create a new
thread, with attributes specified by attr, within a process. If attr is NULL, the default attributes are used. (Seepthread_attr_init(3C)). If the attributes specified by attr
are modified later, the thread's attributes are notaffected. Upon successful completion, pthread_create()
stores the ID of the created thread in the location refer-
enced by thread.The thread is created executing start_routine with arg as
its sole argument. If the start_routine returns, the effect
is as if there was an implicit call to pthread_exit() using
the return value of start_routine as the exit status. Note
that the thread in which main() was originally invoked differs from this. When it returns from main(), the effect is as if there was an implicit call to exit() using the return value of main() as the exit status.The signal state of the new thread is initialised as fol-
lows: o The signal mask is inherited from the creating thread. o The set of signals pending for the new thread is empty. Default thread creation:pthread_t tid;
void *start_func(void *), *arg;
pthread_create(&tid, NULL, start_func, arg);
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This would have the same effect as:pthread_attr_t attr;
pthread_attr_init(&attr); /* initialize attr with default */
/* attributes */pthread_create(&tid, &attr, start_func, arg);
User-defined thread creation: To create a thread that is
scheduled on a system-wide basis, use:
pthread_attr_init(&attr); /* initialize attr with default */
/* attributes */pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM);
/* system-wide contention */
pthread_create(&tid, &attr, start_func, arg);
To customize the attributes for POSIX threads, seepthread_attr_init(3C).
A new thread created with pthread_create() uses the stack
specified by the stackaddr attribute, and the stack contin-
ues for the number of bytes specified by the stacksizeattribute. By default, the stack size is 1 megabyte for 32-
bit processes and 2 megabyte for 64-bit processes (see
pthread_attr_setstacksize(3C)). If the default is used for
both the stackaddr and stacksize attributes,pthread_create() creates a stack for the new thread with at
least 1 megabyte for 32-bit processes and 2 megabyte for
64-bit processes. (For customizing stack sizes, see NOTES).
If pthread_create() fails, no new thread is created and the
contents of the location referenced by thread are undefined.RETURN VALUES
If successful, the pthread_create() function returns 0.
Otherwise, an error number is returned to indicate the error.ERRORS
The pthread_create() function will fail if:
EAGAIN The system lacked the necessary resources tocreate another thread, or the system-imposed limit
on the total number of threads in a processPTHREAD_THREADS_MAX would be exceeded.
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EINVAL The value specified by attr is invalid. EPERM The caller does not have appropriate permission toset the required scheduling parameters or schedul-
ing policy.EXAMPLES
Example 1 Example of concurrency with multithreadingThe following is an example of concurrency with multithread-
ing. Since POSIX threads and Solaris threads are fully com-
patible even within the same process, this example usespthread_create() if you execute a.out 0, or thr_create() if
you execute a.out 1. Five threads are created that simultaneously perform atime-consuming function, sleep(10). If the execution of this
process is timed, the results will show that all five indi-
vidual calls to sleep for ten-seconds completed in about ten
seconds, even on a uniprocessor. If a single-threaded pro-
cess calls sleep(10) five times, the execution time will beabout 50-seconds.
The command-line to time this process is:
POSIX threading /usr/bin/time a.out 0 Solaris threading /usr/bin/time a.out 1/* cc thisfile.c -lthread -lpthread */
#define _REENTRANT /* basic 3-lines for threads */
#include
#include
#define NUM_THREADS 5
#define SLEEP_TIME 10
void *sleeping(void *); /* thread routine */ int i;thread_t tid[NUM_THREADS]; /* array of thread IDs */
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main(int argc, char *argv[]) { if (argc == 1) {printf("use 0 as arg1 to use pthread_create()\n");
printf("or use 1 as arg1 to use thr_create()\n");
return (1); } switch (*argv[1]) { case '0': /* POSIX */for ( i = 0; i < NUM_THREADS; i++)
pthread_create(&tid[i], NULL, sleeping,
(void *)SLEEP_TIME);
for ( i = 0; i < NUM_THREADS; i++)
pthread_join(tid[i], NULL);
break; case '1': /* Solaris */for ( i = 0; i < NUM_THREADS; i++)
thr_create(NULL, 0, sleeping, (void *)SLEEP_TIME, 0,
&tid[i]);while (thr_join(0, NULL, NULL) == 0)
; break; } /* switch */printf("main() reporting that all %d threads have
terminated\n", i); return (0); } /* main */ void * sleeping(void *arg) {int sleep_time = (int)arg;
printf("thread %d sleeping %d seconds ...\n", thr_self(),
sleep_time);
sleep(sleep_time);
printf("\nthread %d awakening\n", thr_self());
return (NULL); } If main() had not waited for the completion of the otherthreads (using pthread_join(3C) or thr_join(3C)), it would
have continued to process concurrently until it reached the end of its routine and the entire process would have exited prematurely. See exit(2).ATTRIBUTES
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See attributes(5) for descriptions of the following attri-
butes:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Committed ||_____________________________|_____________________________|
| MT-Level | MT-Safe |
|_____________________________|_____________________________|
| Standard | See standards(5). ||_____________________________|_____________________________|
SEE ALSO
fork(2), pthread_attr_init(3C), pthread_cancel(3C),
pthread_exit(3C), pthread_join(3C), sysconf(3C), attri-
butes(5), standards(5) NOTES Multithreaded application threads execute independently of each other, so their relative behavior is unpredictable. Therefore, it is possible for the thread executing main() to finish before all other user application threads. Thepthread_join(3C)function, on the other hand, must specify
the terminating thread (IDs) for which it will wait.A user-specified stack size must be greater than the value
PTHREAD_STACK_MIN. A minimum stack size may not accommodate
the stack frame for the user thread function start_func. If
a stack size is specified, it must accommodate start_func
requirements and the functions that it may call in turn, in addition to the minimum requirement. It is usually very difficult to determine the runtime stackrequirements for a thread. PTHREAD_STACK_MIN specifies how
much stack storage is required to execute a NULL start_func.
The total runtime requirements for stack storage are depen-
dent on the storage required to do runtime linking, the amount of storage required by library runtimes (as printf()) that your thread calls. Since these storage parameters are not known before the program runs, it is best to use default stacks. If you know your runtime requirements or decide to use stacks that are larger than the default, then it makes sense to specify your own stacks.SunOS 5.11 Last change: 23 Mar 2005 5