mirror of https://github.com/mkerrisk/man-pages
378 lines
11 KiB
Groff
378 lines
11 KiB
Groff
.\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH PTHREAD_CREATE 3 2008-11-11 "Linux" "Linux Programmer's Manual"
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.SH NAME
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pthread_create \- create a new thread
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.SH SYNOPSIS
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.nf
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.B #include <pthread.h>
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.BI "int pthread_create(pthread_t *" thread ", const pthread_attr_t *" attr ,
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.BI " void *(*" start_routine ") (void *), void *" arg );
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.fi
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.sp
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Compile and link with \fI\-pthread\fP.
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.SH DESCRIPTION
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The
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.BR pthread_create ()
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function starts a new thread in the calling process.
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The new thread starts execution by invoking
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.IR start_routine ();
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.IR arg
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is passed as the sole argument of
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.IR start_routine ().
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The new thread terminates in one of the following ways:
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.IP * 2
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It calls
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.BR pthread_exit (3),
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specifying an exit status value that is available to another thread
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in the same process that calls
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.BR pthread_join (3).
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.IP *
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It returns from
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.IR start_routine ().
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This is equivalent to calling
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.BR pthread_exit (3)
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with the value supplied in the
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.I return
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statement.
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.IP *
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It is canceled (see
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.BR pthread_cancel (3)).
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.IP *
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Any of the threads in the process calls
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.BR exit (3),
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or the main thread performs a return from
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.IR main ().
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This causes the termination of all threads in the process.
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.PP
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The
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.I attr
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argument points to a
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.I pthread_attr_t
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structure whose contents are used at thread creation time to
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determine attributes for the new thread;
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this structure is initialized using
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.BR pthread_attr_init (3)
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and related functions.
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If
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.I attr
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is NULL,
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then the thread is created with default attributes.
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Before returning, a successful call to
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.BR pthread_create ()
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stores the ID of the new thread in the buffer pointed to by
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.IR thread ;
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this identifier is used to refer to the thread
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in subsequent calls to other pthreads functions.
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The new thread inherits a copy of the creating thread's signal mask
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.RB ( pthread_sigmask (3)).
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The set of pending signals for the new thread is empty
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.RB ( sigpending (2)).
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The new thread does not inherit the creating thread's
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alternate signal stack
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.RB ( sigaltstack (2)).
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The new thread inherits the calling thread's floating-point environment
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.RB ( fenv (3)).
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The initial value of the new thread's CPU-time clock is 0
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(see
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.BR pthread_getcpuclockid (3)).
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.\" CLOCK_THREAD_CPUTIME_ID in clock_gettime(3)
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.SS Linux-specific details
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The new thread inherits copies of the calling thread's capability sets
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(see
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.BR capabilities (7))
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and CPU affinity mask (see
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.BR sched_setaffinity (2)).
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.SH RETURN VALUE
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On success,
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.BR pthread_create ()
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returns 0;
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on error, it returns an error number, and the contents of
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.IR *thread
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are undefined.
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.SH ERRORS
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.TP
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.B EAGAIN
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Insufficient resources to create another thread,
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or a system-imposed limit on the number of threads was encountered.
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The latter case may occur in two ways:
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the
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.BR RLIMIT_NPROC
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soft resource limit (set via
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.BR setrlimit (2)),
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which limits the number of process for a real user ID,
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was reached;
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or the kernel's system-wide limit on the number of threads,
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.IR /proc/sys/kernel/threads-max ,
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was reached.
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.TP
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.B EINVAL
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Invalid settings in
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.IR attr .
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.TP
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.\" FIXME . Test the following
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.B EPERM
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No permission to set the scheduling policy and parameters specified in
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.IR attr .
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.SH CONFORMING TO
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POSIX.1-2001.
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.SH NOTES
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See
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.BR pthread_self (3)
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for further information on the thread ID returned in
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.IR *thread
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by
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.BR pthread_create ().
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Unless real-time scheduling policies are being employed,
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after a call to
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.BR pthread_create (),
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it is indeterminate which thread\(emthe caller or the new thread\(emwill
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next execute.
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A thread may either be
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.I joinable
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or
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.IR detached .
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If a thread is joinable, then another thread can call
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.BR pthread_join (3)
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to wait for the thread to terminate and fetch its exit status.
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Only when a terminated joinable thread has been joined are
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the last of its resources released back to the system.
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When a detached thread terminates,
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its resources are automatically released back to the system:
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it is not possible to join with the thread in order to obtain
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its exit status.
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Making a thread detached is useful for some types of daemon threads
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whose exit status the application does not need to care about.
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By default, a new thread is created in a joinable state, unless
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.I attr
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was set to create the thread in a detached state (using
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.BR pthread_attr_setdetachstate (3)).
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.\" FIXME . Perhaps some of the following detail should be in
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.\" a future pthread_attr_setstacksize(3) page.
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On Linux/x86-32, the default stack size for a new thread is 2 megabytes.
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Under the NPTL threading implementation, if the
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.BR RLIMIT_STACK
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soft resource limit
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.IR "at the time the program started"
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has any value other than "unlimited",
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then it determines the default stack size of new threads.
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Using
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.BR pthread_attr_setstacksize (3),
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the stack size attribute can be explicitly set in the
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.I attr
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argument used to create a thread,
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in order to obtain a stack size other than the default.
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.SH EXAMPLE
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The program below demonstrates the use of
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.BR pthread_create (),
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as well as a number of other functions in the pthreads API.
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In the following run,
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on a system providing the NPTL threading implementation,
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the stack size defaults to the value given by the
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"stack size" resource limit:
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.in +4n
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.nf
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.RB "$" " ulimit \-s"
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8192 # The stack size limit is 8 MB (0x80000 bytes)
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.RB "$" " ./a.out hola salut servus"
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Thread 1: top of stack near 0xb7dd03b8; argv_string=hola
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Thread 2: top of stack near 0xb75cf3b8; argv_string=salut
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Thread 3: top of stack near 0xb6dce3b8; argv_string=servus
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Joined with thread 1; returned value was HOLA
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Joined with thread 2; returned value was SALUT
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Joined with thread 3; returned value was SERVUS
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.fi
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.in
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In the next run, the program explicitly sets a stack size of 1MB (using
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.BR pthread_attr_setstacksize (3))
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for the created threads:
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.in +4n
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.nf
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.RB "$" " ./a.out \-s 0x100000 hola salut servus"
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Thread 1: top of stack near 0xb7d723b8; argv_string=hola
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Thread 2: top of stack near 0xb7c713b8; argv_string=salut
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Thread 3: top of stack near 0xb7b703b8; argv_string=servus
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Joined with thread 1; returned value was HOLA
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Joined with thread 2; returned value was SALUT
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Joined with thread 3; returned value was SERVUS
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.fi
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.in
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.SS Program source
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\&
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.nf
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#include <pthread.h>
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#include <string.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <errno.h>
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#include <ctype.h>
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#define handle_error_en(en, msg) \\
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do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
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#define handle_error(msg) \\
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do { perror(msg); exit(EXIT_FAILURE); } while (0)
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struct thread_info { /* Used as argument to thread_start() */
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pthread_t thread_id; /* ID returned by pthread_create */
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int thread_num; /* Application\-defined thread # */
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char *argv_string; /* From command\-line argument */
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};
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/* Thread start function: display address near top of our stack,
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and return upper\-cased copy of argv_string */
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static void *
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thread_start(void *arg)
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{
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struct thread_info *tinfo = (struct thread_info *) arg;
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char *uargv, *p;
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printf("Thread %d: top of stack near %p; argv_string=%s\\n",
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tinfo\->thread_num, &p, tinfo->argv_string);
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uargv = strdup(tinfo\->argv_string);
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if (uargv == NULL)
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handle_error("strdup");
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for (p = uargv; *p != \(aq\\0\(aq; p++)
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*p = toupper(*p);
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return uargv;
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}
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int
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main(int argc, char *argv[])
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{
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int s, tnum, opt, num_threads;
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struct thread_info *tinfo;
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pthread_attr_t attr;
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int stack_size;
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void *res;
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/* The "\-s" option specifies a stack size for our threads */
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stack_size = \-1;
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while ((opt = getopt(argc, argv, "s:")) != \-1) {
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switch (opt) {
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case \(aqs\(aq:
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stack_size = strtoul(optarg, NULL, 0);
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break;
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default:
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fprintf(stderr, "Usage: %s [\-s stack-size] arg...\\n",
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argv[0]);
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exit(EXIT_FAILURE);
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}
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}
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num_threads = argc \- optind;
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/* Initialize thread creation attributes */
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s = pthread_attr_init(&attr);
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if (s != 0)
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handle_error_en(s, "pthread_attr_init");
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if (stack_size > 0) {
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s = pthread_attr_setstacksize(&attr, stack_size);
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if (s != 0)
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handle_error_en(s, "pthread_attr_setstacksize");
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}
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/* Allocate memory for pthread_create() arguments */
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tinfo = calloc(num_threads, sizeof(struct thread_info));
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if (tinfo == NULL)
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handle_error("calloc");
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/* Create one thread for each command\-line argument */
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for (tnum = 0; tnum < num_threads; tnum++) {
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tinfo[tnum].thread_num = tnum + 1;
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tinfo[tnum].argv_string = argv[optind + tnum];
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/* The pthread_create() call stores the thread ID into
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corresponding element of tinfo[] */
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s = pthread_create(&tinfo[tnum].thread_id, &attr,
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&thread_start, &tinfo[tnum]);
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if (s != 0)
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handle_error_en(s, "pthread_create");
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}
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/* Destroy the thread attributes object, since it is no
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longer needed */
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s = pthread_attr_destroy(&attr);
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if (s != 0)
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handle_error_en(s, "pthread_attr_destroy");
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/* Now join with each thread, and display its returned value */
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for (tnum = 0; tnum < num_threads; tnum++) {
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s = pthread_join(tinfo[tnum].thread_id, &res);
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if (s != 0)
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handle_error_en(s, "pthread_join");
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printf("Joined with thread %d; returned value was %s\\n",
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tinfo[tnum].thread_num, (char *) res);
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free(res); /* Free memory allocated by thread */
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}
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free(tinfo);
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exit(EXIT_SUCCESS);
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}
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.fi
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.SH BUGS
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In the obsolete LinuxThreads implementation,
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each of the threads in a process has a different process ID.
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This is in violation of the POSIX threads specification,
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and is the source of many other non-conformances to the standard; see
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.BR pthreads (7).
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.SH SEE ALSO
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.BR getrlimit (2),
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.BR pthread_attr_init (3),
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.BR pthread_cancel (3),
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.BR pthread_detach (3),
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.BR pthread_equal (3),
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.BR pthread_exit (3),
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.BR pthread_getattr_np (3),
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.BR pthread_join (3),
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.BR pthread_self (3),
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.BR pthreads (7)
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