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PTHREAD_CREATE(3) Linux Programmer's Manual PTHREAD_CREATE(3)
pthread_create - create a new thread
#include <pthread.h>
int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
void *(*start_routine) (void *), void *arg);
Compile and link with -pthread.
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.1-2001, POSIX.1-2008.
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)).
On Linux/x86-32, the default stack size for a new thread is 2
megabytes. 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.
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 1MB
(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 <pthread.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <ctype.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, *p;
printf("Thread %d: top of stack near %p; argv_string=%s\n",
tinfo->thread_num, &p, tinfo->argv_string);
uargv = strdup(tinfo->argv_string);
if (uargv == NULL)
handle_error("strdup");
for (p = uargv; *p != '\0'; p++)
*p = toupper(*p);
return uargv;
}
int
main(int argc, char *argv[])
{
int s, tnum, opt, num_threads;
struct thread_info *tinfo;
pthread_attr_t attr;
int stack_size;
void *res;
/* 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(struct thread_info));
if (tinfo == NULL)
handle_error("calloc");
/* Create one thread for each command-line argument */
for (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 (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 release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2016-12-12 PTHREAD_CREATE(3)
Pages that refer to this page: 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_self(3), pthread_setaffinity_np(3), pthread_setname_np(3), pthread_setschedparam(3), pthread_setschedprio(3), pthread_sigmask(3), pthreads(7)