1PTHREAD_CREATE(3P) POSIX Programmer's Manual PTHREAD_CREATE(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 pthread_create — thread creation
13
15 #include <pthread.h>
16 int pthread_create(pthread_t *restrict thread,
18 const pthread_attr_t *restrict attr,
19 void *(*start_routine)(void*), void *restrict arg);
20
22 The pthread_create() function shall create a new thread, with
23 attributes specified by attr, within a process. If attr is NULL, the
24 default attributes shall be used. If the attributes specified by attr
25 are modified later, the thread's attributes shall not be affected.
26 Upon successful completion, pthread_create() shall store the ID of the
27 created thread in the location referenced by thread.
28 The thread is created executing start_routine with arg as its sole
30 argument. If the start_routine returns, the effect shall be as if there
31 was an implicit call to pthread_exit() using the return value of
32 start_routine as the exit status. Note that the thread in which main()
33 was originally invoked differs from this. When it returns from main(),
34 the effect shall be as if there was an implicit call to exit() using
35 the return value of main() as the exit status.
36 The signal state of the new thread shall be initialized as follows:
38 * The signal mask shall be inherited from the creating thread.
40 * The set of signals pending for the new thread shall be empty.
42 The thread-local current locale and the alternate stack shall not be
44 inherited.
45 The floating-point environment shall be inherited from the creating
47 thread.
48 If pthread_create() fails, no new thread is created and the contents of
50 the location referenced by thread are undefined.
51 If _POSIX_THREAD_CPUTIME is defined, the new thread shall have a CPU-
53 time clock accessible, and the initial value of this clock shall be set
54 to zero.
55 The behavior is undefined if the value specified by the attr argument
57 to pthread_create() does not refer to an initialized thread attributes
58 object.
59
61 If successful, the pthread_create() function shall return zero; other‐
62 wise, an error number shall be returned to indicate the error.
63
65 The pthread_create() function shall fail if:
66 EAGAIN The system lacked the necessary resources to create another
68 thread, or the system-imposed limit on the total number of
69 threads in a process {PTHREAD_THREADS_MAX} would be exceeded.
70 EPERM The caller does not have appropriate privileges to set the
72 required scheduling parameters or scheduling policy.
73 The pthread_create() function shall not return an error code of
75 [EINTR].
76 The following sections are informative.
78
80 None.
81
83 There is no requirement on the implementation that the ID of the cre‐
84 ated thread be available before the newly created thread starts execut‐
85 ing. The calling thread can obtain the ID of the created thread through
86 the thread argument of the pthread_create() function, and the newly
87 created thread can obtain its ID by a call to pthread_self().
88
90 A suggested alternative to pthread_create() would be to define two sep‐
91 arate operations: create and start. Some applications would find such
92 behavior more natural. Ada, in particular, separates the ``creation''
93 of a task from its ``activation''.
94 Splitting the operation was rejected by the standard developers for
96 many reasons:
97 * The number of calls required to start a thread would increase from
99 one to two and thus place an additional burden on applications that
100 do not require the additional synchronization. The second call,
101 however, could be avoided by the additional complication of a
102 start-up state attribute.
103 * An extra state would be introduced: ``created but not started''.
105 This would require the standard to specify the behavior of the
106 thread operations when the target has not yet started executing.
107 * For those applications that require such behavior, it is possible
109 to simulate the two separate steps with the facilities that are
110 currently provided. The start_routine() can synchronize by waiting
111 on a condition variable that is signaled by the start operation.
112 An Ada implementor can choose to create the thread at either of two
114 points in the Ada program: when the task object is created, or when the
115 task is activated (generally at a ``begin''). If the first approach is
116 adopted, the start_routine() needs to wait on a condition variable to
117 receive the order to begin ``activation''. The second approach requires
118 no such condition variable or extra synchronization. In either
119 approach, a separate Ada task control block would need to be created
120 when the task object is created to hold rendezvous queues, and so on.
121 An extension of the preceding model would be to allow the state of the
123 thread to be modified between the create and start. This would allow
124 the thread attributes object to be eliminated. This has been rejected
125 because:
126 * All state in the thread attributes object has to be able to be set
128 for the thread. This would require the definition of functions to
129 modify thread attributes. There would be no reduction in the number
130 of function calls required to set up the thread. In fact, for an
131 application that creates all threads using identical attributes,
132 the number of function calls required to set up the threads would
133 be dramatically increased. Use of a thread attributes object per‐
134 mits the application to make one set of attribute setting function
135 calls. Otherwise, the set of attribute setting function calls
136 needs to be made for each thread creation.
137 * Depending on the implementation architecture, functions to set
139 thread state would require kernel calls, or for other implementa‐
140 tion reasons would not be able to be implemented as macros, thereby
141 increasing the cost of thread creation.
142 * The ability for applications to segregate threads by class would be
144 lost.
145 Another suggested alternative uses a model similar to that for process
147 creation, such as ``thread fork''. The fork semantics would provide
148 more flexibility and the ``create'' function can be implemented simply
149 by doing a thread fork followed immediately by a call to the desired
150 ``start routine'' for the thread. This alternative has these problems:
151 * For many implementations, the entire stack of the calling thread
153 would need to be duplicated, since in many architectures there is
154 no way to determine the size of the calling frame.
155 * Efficiency is reduced since at least some part of the stack has to
157 be copied, even though in most cases the thread never needs the
158 copied context, since it merely calls the desired start routine.
159 If an implementation detects that the value specified by the attr argu‐
161 ment to pthread_create() does not refer to an initialized thread
162 attributes object, it is recommended that the function should fail and
163 report an [EINVAL] error.
164
166 None.
167
169 fork(), pthread_exit(), pthread_join()
170 The Base Definitions volume of POSIX.1‐2017, Section 4.12, Memory Syn‐
172 chronization, <pthread.h>
173
175 Portions of this text are reprinted and reproduced in electronic form
176 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
177 table Operating System Interface (POSIX), The Open Group Base Specifi‐
178 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
179 Electrical and Electronics Engineers, Inc and The Open Group. In the
180 event of any discrepancy between this version and the original IEEE and
181 The Open Group Standard, the original IEEE and The Open Group Standard
182 is the referee document. The original Standard can be obtained online
183 at http://www.opengroup.org/unix/online.html .
184 Any typographical or formatting errors that appear in this page are
186 most likely to have been introduced during the conversion of the source
187 files to man page format. To report such errors, see https://www.ker‐
188 nel.org/doc/man-pages/reporting_bugs.html .
189IEEE/The Open Group 2017 PTHREAD_CREATE(3P)