1PTHREAD_CREATE(3) Linux Programmer's Manual PTHREAD_CREATE(3)
2
6 pthread_create - create a new thread
7
9 #include <pthread.h>
10 int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
12 void *(*start_routine) (void *), void *arg);
13 Compile and link with -pthread.
15
17 The pthread_create() function starts a new thread in the calling
18 process. The new thread starts execution by invoking start_routine();
19 arg is passed as the sole argument of start_routine().
20 The new thread terminates in one of the following ways:
22 * It calls pthread_exit(3), specifying an exit status value that is
24 available to another thread in the same process that calls
25 pthread_join(3).
26 * It returns from start_routine(). This is equivalent to calling
28 pthread_exit(3) with the value supplied in the return statement.
29 * It is canceled (see pthread_cancel(3)).
31 * Any of the threads in the process calls exit(3), or the main thread
33 performs a return from main(). This causes the termination of all
34 threads in the process.
35 The attr argument points to a pthread_attr_t structure whose contents
37 are used at thread creation time to determine attributes for the new
38 thread; this structure is initialized using pthread_attr_init(3) and
39 related functions. If attr is NULL, then the thread is created with
40 default attributes.
41 Before returning, a successful call to pthread_create() stores the ID
43 of the new thread in the buffer pointed to by thread; this identifier
44 is used to refer to the thread in subsequent calls to other pthreads
45 functions.
46 The new thread inherits a copy of the creating thread's signal mask
48 (pthread_sigmask(3)). The set of pending signals for the new thread is
49 empty (sigpending(2)). The new thread does not inherit the creating
50 thread's alternate signal stack (sigaltstack(2)).
51 The new thread inherits the calling thread's floating-point environment
53 (fenv(3)).
54 The initial value of the new thread's CPU-time clock is 0 (see
56 pthread_getcpuclockid(3)).
57 Linux-specific details
59 The new thread inherits copies of the calling thread's capability sets
60 (see capabilities(7)) and CPU affinity mask (see sched_setaffinity(2)).
61
63 On success, pthread_create() returns 0; on error, it returns an error
64 number, and the contents of *thread are undefined.
65
67 EAGAIN Insufficient resources to create another thread.
68 EAGAIN A system-imposed limit on the number of threads was encountered.
70 There are a number of limits that may trigger this error: the
71 RLIMIT_NPROC soft resource limit (set via setrlimit(2)), which
72 limits the number of processes and threads for a real user ID,
73 was reached; the kernel's system-wide limit on the number of
74 processes and threads, /proc/sys/kernel/threads-max, was reached
75 (see proc(5)); or the maximum number of PIDs, /proc/sys/ker‐
76 nel/pid_max, was reached (see proc(5)).
77 EINVAL Invalid settings in attr.
79 EPERM No permission to set the scheduling policy and parameters speci‐
81 fied in attr.
82
84 For an explanation of the terms used in this section, see
85 attributes(7).
86 ┌─────────────────┬───────────────┬─────────┐
88 │Interface │ Attribute │ Value │
89 ├─────────────────┼───────────────┼─────────┤
90 │pthread_create() │ Thread safety │ MT-Safe │
91 └─────────────────┴───────────────┴─────────┘
92
94 POSIX.1-2001, POSIX.1-2008.
95
97 See pthread_self(3) for further information on the thread ID returned
98 in *thread by pthread_create(). Unless real-time scheduling policies
99 are being employed, after a call to pthread_create(), it is indetermi‐
100 nate which thread—the caller or the new thread—will next execute.
101 A thread may either be joinable or detached. If a thread is joinable,
103 then another thread can call pthread_join(3) to wait for the thread to
104 terminate and fetch its exit status. Only when a terminated joinable
105 thread has been joined are the last of its resources released back to
106 the system. When a detached thread terminates, its resources are auto‐
107 matically released back to the system: it is not possible to join with
108 the thread in order to obtain its exit status. Making a thread
109 detached is useful for some types of daemon threads whose exit status
110 the application does not need to care about. By default, a new thread
111 is created in a joinable state, unless attr was set to create the
112 thread in a detached state (using pthread_attr_setdetachstate(3)).
113 Under the NPTL threading implementation, if the RLIMIT_STACK soft
115 resource limit at the time the program started has any value other than
116 "unlimited", then it determines the default stack size of new threads.
117 Using pthread_attr_setstacksize(3), the stack size attribute can be
118 explicitly set in the attr argument used to create a thread, in order
119 to obtain a stack size other than the default. If the RLIMIT_STACK
120 resource limit is set to "unlimited", a per-architecture value is used
121 for the stack size. Here is the value for a few architectures:
122 ┌─────────────┬────────────────────┐
124 │Architecture │ Default stack size │
125 ├─────────────┼────────────────────┤
126 │i386 │ 2 MB │
127 ├─────────────┼────────────────────┤
128 │IA-64 │ 32 MB │
129 ├─────────────┼────────────────────┤
130 │PowerPC │ 4 MB │
131 ├─────────────┼────────────────────┤
132 │S/390 │ 2 MB │
133 ├─────────────┼────────────────────┤
134 │Sparc-32 │ 2 MB │
135 ├─────────────┼────────────────────┤
136 │Sparc-64 │ 4 MB │
137 ├─────────────┼────────────────────┤
138 │x86_64 │ 2 MB │
139 └─────────────┴────────────────────┘
141 In the obsolete LinuxThreads implementation, each of the threads in a
142 process has a different process ID. This is in violation of the POSIX
143 threads specification, and is the source of many other nonconformances
144 to the standard; see pthreads(7).
145
147 The program below demonstrates the use of pthread_create(), as well as
148 a number of other functions in the pthreads API.
149 In the following run, on a system providing the NPTL threading imple‐
151 mentation, the stack size defaults to the value given by the "stack
152 size" resource limit:
153 $ ulimit -s
155 8192 # The stack size limit is 8 MB (0x800000 bytes)
156 $ ./a.out hola salut servus
157 Thread 1: top of stack near 0xb7dd03b8; argv_string=hola
158 Thread 2: top of stack near 0xb75cf3b8; argv_string=salut
159 Thread 3: top of stack near 0xb6dce3b8; argv_string=servus
160 Joined with thread 1; returned value was HOLA
161 Joined with thread 2; returned value was SALUT
162 Joined with thread 3; returned value was SERVUS
163 In the next run, the program explicitly sets a stack size of 1 MB
165 (using pthread_attr_setstacksize(3)) for the created threads:
166 $ ./a.out -s 0x100000 hola salut servus
168 Thread 1: top of stack near 0xb7d723b8; argv_string=hola
169 Thread 2: top of stack near 0xb7c713b8; argv_string=salut
170 Thread 3: top of stack near 0xb7b703b8; argv_string=servus
171 Joined with thread 1; returned value was HOLA
172 Joined with thread 2; returned value was SALUT
173 Joined with thread 3; returned value was SERVUS
174 Program source
176 #include <pthread.h>
178 #include <string.h>
179 #include <stdio.h>
180 #include <stdlib.h>
181 #include <unistd.h>
182 #include <errno.h>
183 #include <ctype.h>
184 #define handle_error_en(en, msg) \
186 do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
187 #define handle_error(msg) \
189 do { perror(msg); exit(EXIT_FAILURE); } while (0)
190 struct thread_info { /* Used as argument to thread_start() */
192 pthread_t thread_id; /* ID returned by pthread_create() */
193 int thread_num; /* Application-defined thread # */
194 char *argv_string; /* From command-line argument */
195 };
196 /* Thread start function: display address near top of our stack,
198 and return upper-cased copy of argv_string */
199 static void *
201 thread_start(void *arg)
202 {
203 struct thread_info *tinfo = arg;
204 char *uargv, *p;
205 printf("Thread %d: top of stack near %p; argv_string=%s\n",
207 tinfo->thread_num, &p, tinfo->argv_string);
208 uargv = strdup(tinfo->argv_string);
210 if (uargv == NULL)
211 handle_error("strdup");
212 for (p = uargv; *p != '\0'; p++)
214 *p = toupper(*p);
215 return uargv;
217 }
218 int
220 main(int argc, char *argv[])
221 {
222 int s, tnum, opt, num_threads;
223 struct thread_info *tinfo;
224 pthread_attr_t attr;
225 int stack_size;
226 void *res;
227 /* The "-s" option specifies a stack size for our threads */
229 stack_size = -1;
231 while ((opt = getopt(argc, argv, "s:")) != -1) {
232 switch (opt) {
233 case 's':
234 stack_size = strtoul(optarg, NULL, 0);
235 break;
236 default:
238 fprintf(stderr, "Usage: %s [-s stack-size] arg...\n",
239 argv[0]);
240 exit(EXIT_FAILURE);
241 }
242 }
243 num_threads = argc - optind;
245 /* Initialize thread creation attributes */
247 s = pthread_attr_init(&attr);
249 if (s != 0)
250 handle_error_en(s, "pthread_attr_init");
251 if (stack_size > 0) {
253 s = pthread_attr_setstacksize(&attr, stack_size);
254 if (s != 0)
255 handle_error_en(s, "pthread_attr_setstacksize");
256 }
257 /* Allocate memory for pthread_create() arguments */
259 tinfo = calloc(num_threads, sizeof(struct thread_info));
261 if (tinfo == NULL)
262 handle_error("calloc");
263 /* Create one thread for each command-line argument */
265 for (tnum = 0; tnum < num_threads; tnum++) {
267 tinfo[tnum].thread_num = tnum + 1;
268 tinfo[tnum].argv_string = argv[optind + tnum];
269 /* The pthread_create() call stores the thread ID into
271 corresponding element of tinfo[] */
272 s = pthread_create(&tinfo[tnum].thread_id, &attr,
274 &thread_start, &tinfo[tnum]);
275 if (s != 0)
276 handle_error_en(s, "pthread_create");
277 }
278 /* Destroy the thread attributes object, since it is no
280 longer needed */
281 s = pthread_attr_destroy(&attr);
283 if (s != 0)
284 handle_error_en(s, "pthread_attr_destroy");
285 /* Now join with each thread, and display its returned value */
287 for (tnum = 0; tnum < num_threads; tnum++) {
289 s = pthread_join(tinfo[tnum].thread_id, &res);
290 if (s != 0)
291 handle_error_en(s, "pthread_join");
292 printf("Joined with thread %d; returned value was %s\n",
294 tinfo[tnum].thread_num, (char *) res);
295 free(res); /* Free memory allocated by thread */
296 }
297 free(tinfo);
299 exit(EXIT_SUCCESS);
300 }
301
303 getrlimit(2), pthread_attr_init(3), pthread_cancel(3),
304 pthread_detach(3), pthread_equal(3), pthread_exit(3),
305 pthread_getattr_np(3), pthread_join(3), pthread_self(3),
306 pthread_setattr_default_np(3), pthreads(7)
307
309 This page is part of release 5.02 of the Linux man-pages project. A
310 description of the project, information about reporting bugs, and the
311 latest version of this page, can be found at
312 https://www.kernel.org/doc/man-pages/.
313Linux 2018-04-30 PTHREAD_CREATE(3)