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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | NOTES | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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pthread_create(3) Library Functions Manual pthread_create(3)
pthread_create - create a new thread
POSIX threads library (libpthread, -lpthread)
#include <pthread.h>
int pthread_create(pthread_t *restrict thread,
const pthread_attr_t *restrict attr,
typeof(void *(void *)) *start_routine,
void *restrict arg);
The pthread_create() function starts a new thread in the calling
process. The new thread starts execution by invoking
start_routine(); arg is passed as the sole argument of
start_routine().
The new thread terminates in one of the following ways:
• It calls pthread_exit(3), specifying an exit status value that
is available to another thread in the same process that calls
pthread_join(3).
• It returns from start_routine(). This is equivalent to calling
pthread_exit(3) with the value supplied in the return
statement.
• It is canceled (see pthread_cancel(3)).
• Any of the threads in the process calls exit(3), or the main
thread performs a return from main(). This causes the
termination of all threads in the process.
The attr argument points to a pthread_attr_t structure whose
contents are used at thread creation time to determine attributes
for the new thread; this structure is initialized using
pthread_attr_init(3) and related functions. If attr is NULL, then
the thread is created with default attributes.
Before returning, a successful call to pthread_create() stores the
ID of the new thread in the buffer pointed to by thread; this
identifier is used to refer to the thread in subsequent calls to
other pthreads functions.
The new thread inherits a copy of the creating thread's signal
mask (pthread_sigmask(3)). The set of pending signals for the new
thread is empty (sigpending(2)). The new thread does not inherit
the creating thread's alternate signal stack (sigaltstack(2)).
The new thread inherits the calling thread's floating-point
environment (fenv(3)).
The initial value of the new thread's CPU-time clock is 0 (see
pthread_getcpuclockid(3)).
Linux-specific details
The new thread inherits copies of the calling thread's capability
sets (see capabilities(7)) and CPU affinity mask (see
sched_setaffinity(2)).
On success, pthread_create() returns 0; on error, it returns an
error number, and the contents of *thread are undefined.
EAGAIN Insufficient resources to create another thread.
EAGAIN A system-imposed limit on the number of threads was
encountered. There are a number of limits that may trigger
this error: the RLIMIT_NPROC soft resource limit (set via
setrlimit(2)), which limits the number of processes and
threads for a real user ID, was reached; the kernel's
system-wide limit on the number of processes and threads,
/proc/sys/kernel/threads-max, was reached (see proc(5)); or
the maximum number of PIDs, /proc/sys/kernel/pid_max, was
reached (see proc(5)).
EINVAL Invalid settings in attr.
EPERM No permission to set the scheduling policy and parameters
specified in attr.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ pthread_create() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
POSIX.1-2008.
POSIX.1-2001.
See pthread_self(3) for further information on the thread ID
returned in *thread by pthread_create(). Unless real-time
scheduling policies are being employed, after a call to
pthread_create(), it is indeterminate which thread—the caller or
the new thread—will next execute.
A thread may either be joinable or detached. If a thread is
joinable, then another thread can call pthread_join(3) to wait for
the thread to terminate and fetch its exit status. Only when a
terminated joinable thread has been joined are the last of its
resources released back to the system. When a detached thread
terminates, its resources are automatically released back to the
system: it is not possible to join with the thread in order to
obtain its exit status. Making a thread detached is useful for
some types of daemon threads whose exit status the application
does not need to care about. By default, a new thread is created
in a joinable state, unless attr was set to create the thread in a
detached state (using pthread_attr_setdetachstate(3)).
Under the NPTL threading implementation, if the RLIMIT_STACK soft
resource limit at the time the program started has any value other
than "unlimited", then it determines the default stack size of new
threads. Using pthread_attr_setstacksize(3), the stack size
attribute can be explicitly set in the attr argument used to
create a thread, in order to obtain a stack size other than the
default. If the RLIMIT_STACK resource limit is set to
"unlimited", a per-architecture value is used for the stack size:
2 MB on most architectures; 4 MB on POWER and Sparc-64.
In the obsolete LinuxThreads implementation, each of the threads
in a process has a different process ID. This is in violation of
the POSIX threads specification, and is the source of many other
nonconformances to the standard; see pthreads(7).
The program below demonstrates the use of pthread_create(), as
well as a number of other functions in the pthreads API.
In the following run, on a system providing the NPTL threading
implementation, the stack size defaults to the value given by the
"stack size" resource limit:
$ ulimit -s
8192 # The stack size limit is 8 MB (0x800000 bytes)
$ ./a.out hola salut servus
Thread 1: top of stack near 0xb7dd03b8; argv_string=hola
Thread 2: top of stack near 0xb75cf3b8; argv_string=salut
Thread 3: top of stack near 0xb6dce3b8; argv_string=servus
Joined with thread 1; returned value was HOLA
Joined with thread 2; returned value was SALUT
Joined with thread 3; returned value was SERVUS
In the next run, the program explicitly sets a stack size of 1 MB
(using pthread_attr_setstacksize(3)) for the created threads:
$ ./a.out -s 0x100000 hola salut servus
Thread 1: top of stack near 0xb7d723b8; argv_string=hola
Thread 2: top of stack near 0xb7c713b8; argv_string=salut
Thread 3: top of stack near 0xb7b703b8; argv_string=servus
Joined with thread 1; returned value was HOLA
Joined with thread 2; returned value was SALUT
Joined with thread 3; returned value was SERVUS
Program source
#include <ctype.h>
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#define handle_error_en(en, msg) \
do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
#define handle_error(msg) \
do { perror(msg); exit(EXIT_FAILURE); } while (0)
struct thread_info { /* Used as argument to thread_start() */
pthread_t thread_id; /* ID returned by pthread_create() */
int thread_num; /* Application-defined thread # */
char *argv_string; /* From command-line argument */
};
/* Thread start function: display address near top of our stack,
and return upper-cased copy of argv_string. */
static void *
thread_start(void *arg)
{
struct thread_info *tinfo = arg;
char *uargv;
printf("Thread %d: top of stack near %p; argv_string=%s\n",
tinfo->thread_num, (void *) &tinfo, tinfo->argv_string);
uargv = strdup(tinfo->argv_string);
if (uargv == NULL)
handle_error("strdup");
for (char *p = uargv; *p != '\0'; p++)
*p = toupper(*p);
return uargv;
}
int
main(int argc, char *argv[])
{
int s, opt;
void *res;
size_t num_threads;
ssize_t stack_size;
pthread_attr_t attr;
struct thread_info *tinfo;
/* The "-s" option specifies a stack size for our threads. */
stack_size = -1;
while ((opt = getopt(argc, argv, "s:")) != -1) {
switch (opt) {
case 's':
stack_size = strtoul(optarg, NULL, 0);
break;
default:
fprintf(stderr, "Usage: %s [-s stack-size] arg...\n",
argv[0]);
exit(EXIT_FAILURE);
}
}
num_threads = argc - optind;
/* Initialize thread creation attributes. */
s = pthread_attr_init(&attr);
if (s != 0)
handle_error_en(s, "pthread_attr_init");
if (stack_size > 0) {
s = pthread_attr_setstacksize(&attr, stack_size);
if (s != 0)
handle_error_en(s, "pthread_attr_setstacksize");
}
/* Allocate memory for pthread_create() arguments. */
tinfo = calloc(num_threads, sizeof(*tinfo));
if (tinfo == NULL)
handle_error("calloc");
/* Create one thread for each command-line argument. */
for (size_t tnum = 0; tnum < num_threads; tnum++) {
tinfo[tnum].thread_num = tnum + 1;
tinfo[tnum].argv_string = argv[optind + tnum];
/* The pthread_create() call stores the thread ID into
corresponding element of tinfo[]. */
s = pthread_create(&tinfo[tnum].thread_id, &attr,
&thread_start, &tinfo[tnum]);
if (s != 0)
handle_error_en(s, "pthread_create");
}
/* Destroy the thread attributes object, since it is no
longer needed. */
s = pthread_attr_destroy(&attr);
if (s != 0)
handle_error_en(s, "pthread_attr_destroy");
/* Now join with each thread, and display its returned value. */
for (size_t tnum = 0; tnum < num_threads; tnum++) {
s = pthread_join(tinfo[tnum].thread_id, &res);
if (s != 0)
handle_error_en(s, "pthread_join");
printf("Joined with thread %d; returned value was %s\n",
tinfo[tnum].thread_num, (char *) res);
free(res); /* Free memory allocated by thread */
}
free(tinfo);
exit(EXIT_SUCCESS);
}
getrlimit(2), pthread_attr_init(3), pthread_cancel(3),
pthread_detach(3), pthread_equal(3), pthread_exit(3),
pthread_getattr_np(3), pthread_join(3), pthread_self(3),
pthread_setattr_default_np(3), pthreads(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 pthread_create(3)
Pages that refer to this page: mmap(2), spu_run(2), wait(2), pthread_attr_init(3), pthread_attr_setdetachstate(3), pthread_attr_setguardsize(3), pthread_attr_setinheritsched(3), pthread_attr_setschedparam(3), pthread_attr_setschedpolicy(3), pthread_attr_setscope(3), pthread_attr_setstack(3), pthread_attr_setstackaddr(3), pthread_attr_setstacksize(3), pthread_cancel(3), pthread_detach(3), pthread_equal(3), pthread_exit(3), pthread_getattr_default_np(3), pthread_getattr_np(3), pthread_join(3), pthread_key_create(3), pthread_self(3), pthread_setaffinity_np(3), pthread_setname_np(3), pthread_setschedparam(3), pthread_setschedprio(3), pthread_sigmask(3), pthreads(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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