pthread_create(3) - Linux manual page (original) (raw)
pthreadcreate(3) Library Functions Manual pthreadcreate(3)
NAME top
pthread_create - create a new threadLIBRARY top
POSIX threads library (_libpthread_, _-lpthread_)SYNOPSIS top
**#include <pthread.h>**
**int pthread_create(pthread_t *restrict** _thread_**,**
**const pthread_attr_t *restrict** _attr_**,**
**typeof(void *(void *)) ***_startroutine_**,**
**void *restrict** _arg_**);**DESCRIPTION top
The **pthread_create**() function starts a new thread in the calling
process. The new thread starts execution by invoking
_startroutine_(); _arg_ is passed as the sole argument of
_startroutine_().
The new thread terminates in one of the following ways:
• It calls [pthread_exit(3)](../man3/pthread%5Fexit.3.html), specifying an exit status value that
is available to another thread in the same process that calls
[pthread_join(3)](../man3/pthread%5Fjoin.3.html).
• It returns from _startroutine_(). This is equivalent to calling
[pthread_exit(3)](../man3/pthread%5Fexit.3.html) with the value supplied in the _return_
statement.
• It is canceled (see [pthread_cancel(3)](../man3/pthread%5Fcancel.3.html)).
• Any of the threads in the process calls [exit(3)](../man3/exit.3.html), 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 _pthreadattrt_ 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)](../man3/pthread%5Fattr%5Finit.3.html) 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)](../man3/pthread%5Fsigmask.3.html)). The set of pending signals for the new
thread is empty ([sigpending(2)](../man2/sigpending.2.html)). The new thread does not inherit
the creating thread's alternate signal stack ([sigaltstack(2)](../man2/sigaltstack.2.html)).
The new thread inherits the calling thread's floating-point
environment ([fenv(3)](../man3/fenv.3.html)).
The initial value of the new thread's CPU-time clock is 0 (see
[pthread_getcpuclockid(3)](../man3/pthread%5Fgetcpuclockid.3.html)).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)).
RETURN VALUE top
On success, **pthread_create**() returns 0; on error, it returns an
error number, and the contents of _*thread_ are undefined.ERRORS top
**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)](../man2/setrlimit.2.html)), 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)](../man5/proc.5.html)); or
the maximum number of PIDs, _/proc/sys/kernel/pidmax_, was
reached (see [proc(5)](../man5/proc.5.html)).
**EINVAL** Invalid settings in _attr_.
**EPERM** No permission to set the scheduling policy and parameters
specified in _attr_.ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ **Interface** │ **Attribute** │ **Value** │
├──────────────────────────────────────┼───────────────┼─────────┤
│ **pthread_create**() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘STANDARDS top
POSIX.1-2008.HISTORY top
POSIX.1-2001.NOTES top
See [pthread_self(3)](../man3/pthread%5Fself.3.html) 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)](../man3/pthread%5Fjoin.3.html) 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)](../man3/pthread%5Fattr%5Fsetdetachstate.3.html)).
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)](../man3/pthread%5Fattr%5Fsetstacksize.3.html), 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.BUGS top
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)](../man7/pthreads.7.html).EXAMPLES top
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)](../man3/pthread%5Fattr%5Fsetstacksize.3.html)) 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 SERVUSProgram 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);
}SEE ALSO top
[getrlimit(2)](../man2/getrlimit.2.html), [pthread_attr_init(3)](../man3/pthread%5Fattr%5Finit.3.html), [pthread_cancel(3)](../man3/pthread%5Fcancel.3.html),
[pthread_detach(3)](../man3/pthread%5Fdetach.3.html), [pthread_equal(3)](../man3/pthread%5Fequal.3.html), [pthread_exit(3)](../man3/pthread%5Fexit.3.html),
[pthread_getattr_np(3)](../man3/pthread%5Fgetattr%5Fnp.3.html), [pthread_join(3)](../man3/pthread%5Fjoin.3.html), [pthread_self(3)](../man3/pthread%5Fself.3.html),
[pthread_setattr_default_np(3)](../man3/pthread%5Fsetattr%5Fdefault%5Fnp.3.html), [pthreads(7)](../man7/pthreads.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-12-13 pthreadcreate(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)