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pthread_create(3c)
Standard C Library Functions pthread_create(3C)
NAME
pthread_create - create a thread
SYNOPSIS
#include <pthread.h>
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. (See pthread_attr_init(3C)). If the
attributes specified by attr are modified later, the thread's
attributes are not affected. Upon successful completion, pthread_cre‐
ate() stores the ID of the created thread in the location referenced 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_rou‐
tine as the exit status. Note that the thread in which main() was orig‐
inally 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 follows:
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);
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, see
pthread_attr_init(3C).
A new thread created with pthread_create() uses the stack specified by
the stackaddr attribute, and the stack continues for the number of
bytes specified by the stacksize attribute. 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 to create another
thread, or the system-imposed limit on the total number of
threads in a process PTHREAD_THREADS_MAX would be exceeded.
EINVAL The value specified by attr is invalid.
EPERM The caller does not have appropriate permission to set the
required scheduling parameters or scheduling policy.
EXAMPLES
Example 1 Example of concurrency with multithreading
The following is an example of concurrency with multithreading. Since
POSIX threads and Solaris threads are fully compatible even within the
same process, this example uses pthread_create() if you execute a.out
0, or thr_create() if you execute a.out 1.
Five threads are created that simultaneously perform a time-consuming
function, sleep(10). If the execution of this process is timed, the
results will show that all five individual calls to sleep for ten-sec‐
onds completed in about ten seconds, even on a uniprocessor. If a sin‐
gle-threaded process calls sleep(10) five times, the execution time
will be about 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 */
#include <pthread.h>
#include <thread.h>
#define NUM_THREADS 5
#define SLEEP_TIME 10
void *sleeping(void *); /* thread routine */
int i;
thread_t tid[NUM_THREADS]; /* array of thread IDs */
int
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 other threads (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
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelMT-Safe _ Stan‐
dardSee standards(7).
SEE ALSO
fork(2), mmap(2), pthread_attr_init(3C), pthread_cancel(3C),
pthread_exit(3C), pthread_join(3C), sysconf(3C), attributes(7), stan‐
dards(7), sxadm(8)
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 appli‐
cation threads. The pthread_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 spec‐
ified, 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 stack require‐
ments for a thread. PTHREAD_STACK_MIN specifies how much stack storage
is required to execute a NULL start_func. The total runtime require‐
ments for stack storage are dependent 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.
If the ADISTACK security extension is enabled for the process, and
stackaddr is set to the default value, the stack allocated by the sys‐
tem for the new thread is mapped with ADI enabled. If stackaddr is set
to user-specified memory, ADI must be enabled on the specified memory
in order to extend coverage to the stack. See mmap(2) and sxadm(8).
Oracle Solaris 11.4 14 May 2018 pthread_create(3C)