I have started writing some pthreads man pages, and would appreciate
reviewer for them. Any takers?
First off, a page for pthread_create(3).
Cheers,
Michael
.\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
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.TH PTHREAD_CREATE 3 2008-10-19 "Linux" "Linux Programmer's Manual"
.SH NAME
pthread_create \- create a new thread
.SH SYNOPSIS
.nf
.B #include <pthread.h>
.BI "int pthread_create(pthread_t *" thread ", const pthread_attr_t *" attr ,
.BI " void *(*" start_routine ") (void *), void *" arg );
.fi
.sp
Compile and link with \fI\-pthread\fP.
.SH DESCRIPTION
The
.BR pthread_create ()
functions starts a new thread in the calling process.
The new thread starts execution by invoking
.IR start_routine ();
.IR arg
is passed as the sole argument of
.IR start_routine ().
The new thread terminates in one of the following ways:
.IP * 2
It calls
.BR pthread_exit (3),
specifying an exit status value that is available to another thread
in the same process that calls
.BR pthread_join (3).
.IP *
It returns from
.IR start_routine ().
This is equivalent to calling
.BR pthread_exit (3)
with the value supplied in the
.I return
statement.
.IP *
It is canceled (see
.BR pthread_cancel (3)).
.IP *
Any of the threads in the process calls
.BR exit (3),
or the main thread performs a return from
.IR main ().
This causes the termination of all threads in the process.
.PP
The
.I attr
argument points to a
.I pthread_attr_t
structure whose contents are used at thread creation time to
determine attributes for the new thread;
this structure is initialized using
.BR pthread_attr_init (3)
and related functions.
If
.I attr
is NULL,
then the thread is created with default attributes.
Before returning, a successful call to
.BR pthread_create ()
stores the ID of the new thread in the buffer pointed to by
.IR 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
.RB ( pthread_sigmask (3)).
The set of pending signals for the new thread is empty
.RB ( sigpending (2)).
The new thread does not inherit the creating thread's
alternate signal stack
.RB ( sigaltstack (2)).
The new thread inherits the calling thread's floating-point environment
.RB ( fenv (3)).
The initial value of the new thread's CPU-time clock is 0
(see the description of
.\" FIXME . better to mention pthread_getcpuclockid() here?
.BR CLOCK_THREAD_CPUTIME_ID
in
.BR clock_gettime (3)).
.SS Linux-specific details
The new thread inherits a copy of the calling thread's capability sets
(see
.BR capabilities (7)).
The new thread inherits a copy of the calling thread's CPU affinity mask
(see
.BR sched_setaffinity (2)).
.SH RETURN VALUE
On success,
.BR pthread_create ()
returns 0;
on error, it returns an error number, and the contents of
.IR *thread
are undefined.
.SH ERRORS
.TP
.B EAGAIN
Insufficient resources to create another thread,
or a system-imposed limit on the number of threads was encountered.
The latter case may occur in two ways:
the
.BR RLIMIT_NPROC
soft resource limit (set via
.BR setrlimit (2)),
which limits the number of process for a real user ID,
was reached;
or the kernel's system-wide limit on the number of threads,
.IR /proc/sys/kernel/threads-max ,
was reached.
.TP
.B EINVAL
Invalid settings in
.IR attr .
.TP
.B EPERM
No permission to set the scheduling policy and parameters specified in
.IR attr .
.SH CONFORMING TO
POSIX.1-2001.
.SH NOTES
See
.BR pthread_self (3)
for further information on the thread ID returned in
.IR *thread
by
.BR pthread_create ().
Unless real-time scheduling policies are being employed,
after a call to
.BR pthread_create (),
it is indeterminate which thread\(emthe caller or the new thread\(emwill
next execute.
A thread may either be
.I joinable
or
.IR detached .
If a thread is joinable, then another thread can call
.BR 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
.I attr
was set to create the thread in a detached state (using
.BR pthread_attr_setdetachstate (3)).
.\" FIXME . Perhaps some of the following detail should be in
.\" a future pthread_attr_setstacksize(3) page.
On Linux/x86-32, the default stack size for a new thread is 2 megabytes.
Under the NPTL threading implementation, if the
.BR RLIMIT_STACK
soft resource limit
.IR "at the time the program started"
has any value other than "unlimited",
then it determines the default stack size of new threads.
Using
.BR pthread_attr_setstacksize (3),
the stack size attribute can be explicitly set in the
.I attr
argument used to create a thread.
.SH EXAMPLE
The program below demonstrates the use of
.BR 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:
.in +4n
.nf
$ ulimit \-s
8192 # The stack size limit is 8 MB (0x80000 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
.fi
.in
In the next run, the program explicitly sets a stack size of 1MB (using
.BR pthread_attr_setstacksize (3))
for the created threads:
.in +4n
.nf
$ ./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
.fi
.in
.nf
#include <pthread.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <ctype.h>
/* Simple error handling functions */
#define errExit(msg) { perror(msg); exit(EXIT_FAILURE); }
#define errExitEN(en, msg) { errno = en; perror(msg); \\
exit(EXIT_FAILURE); }
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 = (struct thread_info *) 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)
errExit("strdup");
for (p = uargv; *p != \(aq\\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 \(aqs':
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)
errExitEN(s, "pthread_attr_init");
if (stack_size > 0) {
s = pthread_attr_setstacksize(&attr, stack_size);
if (s != 0)
errExitEN(s, "pthread_attr_setstacksize");
}
/* Allocate memory for pthread_create() arguments */
tinfo = calloc(argc \- 1, num_threads);
if (tinfo == NULL)
errExit("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)
errExitEN(s, "pthread_create");
}
/* Destroy the threads attribute object, since it is no
longer needed */
s = pthread_attr_destroy(&attr);
if (s != 0)
errExitEN(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)
errExitEN(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 */
}
exit(EXIT_SUCCESS);
}
.fi
.SH BUGS
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 non-conformances to the standard; see
.BR pthreads (7).
.SH SEE ALSO
.BR pthread_attr_init (3),
.BR pthread_cancel (3),
.BR pthread_detach (3),
.BR pthread_equal (3),
.BR pthread_exit (3),
.BR pthread_getattr_np (3),
.BR pthread_join (3),
.BR pthread_self (3),
.BR pthreads (7)
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