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pthread_create(3) — Linux manual page

NAME \|LIBRARY \|SYNOPSIS \|DESCRIPTION \|RETURN VALUE \|ERRORS \|ATTRIBUTES \|STANDARDS \|HISTORY \|NOTES \|BUGS \|EXAMPLES \|SEE ALSO \|COLOPHON

pthread_create(3)        Library Functions Manualpthread_create(3)

NAME top

       pthread_create - create a new thread

LIBRARY top

       POSIX threads library (libpthread,-lpthread)

SYNOPSIS top

#include <pthread.h>int pthread_create(pthread_t *restrictthread,const pthread_attr_t *restrictattr,typeof(void *(void *)) *start_routine,void *restrictarg);

DESCRIPTION top

       Thepthread_create() function starts a new thread in the calling       process.  The new thread starts execution by invokingstart_routine();arg is passed as the sole argument ofstart_routine().       The new thread terminates in one of the following ways:       •  It callspthread_exit(3), specifying an exit status value that          is available to another thread in the same process that callspthread_join(3).       •  It returns fromstart_routine().  This is equivalent to callingpthread_exit(3) with the value supplied in thereturn          statement.       •  It is canceled (seepthread_cancel(3)).       •  Any of the threads in the process callsexit(3), or the main          thread performs a return frommain().  This causes the          termination of all threads in the process.       Theattr argument points to apthread_attr_t structure whose       contents are used at thread creation time to determine attributes       for the new thread; this structure is initialized usingpthread_attr_init(3) and related functions.  Ifattr is NULL, then       the thread is created with default attributes.       Before returning, a successful call topthread_create() stores the       ID of the new thread in the buffer pointed to bythread; 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 (seepthread_getcpuclockid(3)).Linux-specific details       The new thread inherits copies of the calling thread's capability       sets (seecapabilities(7)) and CPU affinity mask (seesched_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

EAGAINInsufficient resources to create another thread.EAGAINA system-imposed limit on the number of threads was              encountered.  There are a number of limits that may trigger              this error: theRLIMIT_NPROCsoft resource limit (set viasetrlimit(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 (seeproc(5)); or              the maximum number of PIDs,/proc/sys/kernel/pid_max, was              reached (seeproc(5)).EINVALInvalid settings inattr.EPERMNo permission to set the scheduling policy and parameters              specified inattr.

ATTRIBUTES top

       For an explanation of the terms used in this section, seeattributes(7).       ┌──────────────────────────────────────┬───────────────┬─────────┐       │Interface│Attribute│Value│       ├──────────────────────────────────────┼───────────────┼─────────┤       │pthread_create()                     │ Thread safety │ MT-Safe │       └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

       POSIX.1-2008.

HISTORY top

       POSIX.1-2001.

NOTES top

Seepthread_self(3) for further information on the thread ID returned in*thread bypthread_create(). Unless real-time scheduling policies are being employed, after a call topthread_create(), it is indeterminate which thread—the caller or the new thread—will next execute. A thread may either bejoinable ordetached. If a thread is joinable, then another thread can callpthread_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, unlessattr was set to create the thread in a detached state (usingpthread_attr_setdetachstate(3)). Under the NPTL threading implementation, if theRLIMIT_STACKsoft resource limitat the time the program started has any value other than "unlimited", then it determines the default stack size of new threads. Usingpthread_attr_setstacksize(3), the stack size attribute can be explicitly set in theattr argument used to create a thread, in order to obtain a stack size other than the default. If theRLIMIT_STACKresource 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; seepthreads(7).

EXAMPLES top

       The program below demonstrates the use ofpthread_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       (usingpthread_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 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);       }

COLOPHON top

       This page is part of theman-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 isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17pthread_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)