|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
|
|
|
PTHREAD_CREATE(3P) POSIX Programmer's Manual PTHREAD_CREATE(3P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
pthread_create — thread creation
#include <pthread.h>
int pthread_create(pthread_t *restrict thread,
const pthread_attr_t *restrict attr,
void *(*start_routine)(void*), void *restrict arg);
The pthread_create() function shall create a new thread, with
attributes specified by attr, within a process. If attr is NULL,
the default attributes shall be used. If the attributes specified
by attr are modified later, the thread's attributes shall not be
affected. Upon successful completion, pthread_create() shall
store the ID of the created thread in the location referenced by
thread.
The thread is created executing start_routine with arg as its sole
argument. If the start_routine returns, the effect shall be as if
there was an implicit call to pthread_exit() using the return
value of start_routine as the exit status. Note that the thread in
which main() was originally invoked differs from this. When it
returns from main(), the effect shall be as if there was an
implicit call to exit() using the return value of main() as the
exit status.
The signal state of the new thread shall be initialized as
follows:
* The signal mask shall be inherited from the creating thread.
* The set of signals pending for the new thread shall be empty.
The thread-local current locale and the alternate stack shall not
be inherited.
The floating-point environment shall be inherited from the
creating thread.
If pthread_create() fails, no new thread is created and the
contents of the location referenced by thread are undefined.
If _POSIX_THREAD_CPUTIME is defined, the new thread shall have a
CPU-time clock accessible, and the initial value of this clock
shall be set to zero.
The behavior is undefined if the value specified by the attr
argument to pthread_create() does not refer to an initialized
thread attributes object.
If successful, the pthread_create() function shall return zero;
otherwise, an error number shall be returned to indicate the
error.
The pthread_create() function shall fail if:
EAGAIN The system lacked the necessary resources to create another
thread, or the system-imposed limit on the total number of
threads in a process {PTHREAD_THREADS_MAX} would be
exceeded.
EPERM The caller does not have appropriate privileges to set the
required scheduling parameters or scheduling policy.
The pthread_create() function shall not return an error code of
[EINTR].
The following sections are informative.
None.
There is no requirement on the implementation that the ID of the
created thread be available before the newly created thread starts
executing. The calling thread can obtain the ID of the created
thread through the thread argument of the pthread_create()
function, and the newly created thread can obtain its ID by a call
to pthread_self().
A suggested alternative to pthread_create() would be to define two
separate operations: create and start. Some applications would
find such behavior more natural. Ada, in particular, separates the
``creation'' of a task from its ``activation''.
Splitting the operation was rejected by the standard developers
for many reasons:
* The number of calls required to start a thread would increase
from one to two and thus place an additional burden on
applications that do not require the additional
synchronization. The second call, however, could be avoided by
the additional complication of a start-up state attribute.
* An extra state would be introduced: ``created but not
started''. This would require the standard to specify the
behavior of the thread operations when the target has not yet
started executing.
* For those applications that require such behavior, it is
possible to simulate the two separate steps with the
facilities that are currently provided. The start_routine()
can synchronize by waiting on a condition variable that is
signaled by the start operation.
An Ada implementor can choose to create the thread at either of
two points in the Ada program: when the task object is created, or
when the task is activated (generally at a ``begin''). If the
first approach is adopted, the start_routine() needs to wait on a
condition variable to receive the order to begin ``activation''.
The second approach requires no such condition variable or extra
synchronization. In either approach, a separate Ada task control
block would need to be created when the task object is created to
hold rendezvous queues, and so on.
An extension of the preceding model would be to allow the state of
the thread to be modified between the create and start. This would
allow the thread attributes object to be eliminated. This has been
rejected because:
* All state in the thread attributes object has to be able to be
set for the thread. This would require the definition of
functions to modify thread attributes. There would be no
reduction in the number of function calls required to set up
the thread. In fact, for an application that creates all
threads using identical attributes, the number of function
calls required to set up the threads would be dramatically
increased. Use of a thread attributes object permits the
application to make one set of attribute setting function
calls. Otherwise, the set of attribute setting function calls
needs to be made for each thread creation.
* Depending on the implementation architecture, functions to set
thread state would require kernel calls, or for other
implementation reasons would not be able to be implemented as
macros, thereby increasing the cost of thread creation.
* The ability for applications to segregate threads by class
would be lost.
Another suggested alternative uses a model similar to that for
process creation, such as ``thread fork''. The fork semantics
would provide more flexibility and the ``create'' function can be
implemented simply by doing a thread fork followed immediately by
a call to the desired ``start routine'' for the thread. This
alternative has these problems:
* For many implementations, the entire stack of the calling
thread would need to be duplicated, since in many
architectures there is no way to determine the size of the
calling frame.
* Efficiency is reduced since at least some part of the stack
has to be copied, even though in most cases the thread never
needs the copied context, since it merely calls the desired
start routine.
If an implementation detects that the value specified by the attr
argument to pthread_create() does not refer to an initialized
thread attributes object, it is recommended that the function
should fail and report an [EINVAL] error.
None.
fork(3p), pthread_exit(3p), pthread_join(3p)
The Base Definitions volume of POSIX.1‐2017, Section 4.12, Memory
Synchronization, pthread.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard,
the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 PTHREAD_CREATE(3P)
Pages that refer to this page: pthread.h(0p), pthread_attr_destroy(3p), pthread_attr_getdetachstate(3p), pthread_attr_getinheritsched(3p), pthread_attr_getschedparam(3p), pthread_attr_getschedpolicy(3p), pthread_attr_getscope(3p), pthread_attr_getstack(3p), pthread_attr_getstacksize(3p), pthread_condattr_destroy(3p), pthread_condattr_getclock(3p), pthread_condattr_getpshared(3p), pthread_equal(3p), pthread_exit(3p), pthread_join(3p), pthread_mutexattr_destroy(3p), pthread_mutexattr_getprioceiling(3p), pthread_mutexattr_getprotocol(3p), pthread_mutexattr_getpshared(3p), pthread_self(3p)
|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|