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PTHREAD_CREATE(3)

NAME

pthread_create - create a new thread

SYNOPSIS

       #include <pthread.h>

       int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
                          void *(*start_routine) (void *), void *arg);

Compile and link with -pthread.

DESCRIPTION

The pthread_create() function starts a new thread in the calling process. The new thread starts execution by invoking start_routine(); arg is passed as the sole argument of start_routine().

Thread terminate

The new thread terminates in one of the following ways:

1、It calls pthread_exit(3), specifying an exit status value that is available to another thread in the same process that calls pthread_join(3).

2、It returns from start_routine(). This is equivalent to calling pthread_exit(3) with the value supplied in the return statement.

NOTE: 在一些情况下，start_routing可能并不会return，这种情况下线程的terminates往往是由其它线程来控制的；

3、It is canceled (see pthread_cancel(3)).

4、Any of the threads in the process calls exit(3), or the main thread performs a return from main(). This causes the termination of all threads in the process.

The attr argument

The attr argument points to a pthread_attr_t structure whose contents are used at thread creation time to determine attributes for the new thread; this structure is initialized using pthread_attr_init(3) and related functions. If attr is NULL, then the thread is created with default attributes.

Thread ID

Before returning, a successful call to pthread_create() stores the ID of the new thread in the buffer pointed to by thread; this identifier is used to refer to the thread in subsequent calls to other pthreads functions.

Signal mask

The new thread inherits a copy of the creating thread's signal mask (pthread_sigmask(3)). The set of pending signals for the new thread is empty (sigpending(2)). The new thread does not inherit the creating thread's alternate signal stack (sigaltstack(2)).

Floating-point environment

The new thread inherits the calling thread's floating-point environment (fenv(3)).

CPU-time clock

The initial value of the new thread's CPU-time clock is 0 (see pthread_getcpuclockid(3)).

Linux-specific details

The new thread inherits copies of the calling thread's capability sets (see capabilities(7)) and CPU affinity mask (see sched_setaffinity(2)).

NOTES

See pthread_self(3) for further information on the thread ID returned in thread by pthread_create(). Unless real-time scheduling policies are being employed, after a call to pthread_create(), it is indeterminate which thread—the caller or the new thread—will next execute.

joinable or detached

A thread may either be joinable or detached.

If a thread is joinable, then another thread can call 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 attr was set to create the thread in a detached state (using pthread_attr_setdetachstate(3)).

RLIMIT_STACK soft resource limit

Under the NPTL threading implementation, if the RLIMIT_STACK soft resource limit at the time the program started has any value other than "unlimited", then it determines the default stack size of new threads. Using pthread_attr_setstacksize(3), the stack size attribute can be explicitly set in the attr argument used to create a thread, in order to obtain a stack size other than the default. If the RLIMIT_STACK resource limit is set to "unlimited", a per-architecture value is used for the stack size. Here is the value for a few architectures:

              ┌─────────────┬────────────────────┐
              │Architecture │ Default stack size │
              ├─────────────┼────────────────────┤
              │i386         │               2 MB │
              ├─────────────┼────────────────────┤
              │IA-64        │              32 MB │
              ├─────────────┼────────────────────┤
              │PowerPC      │               4 MB │
              ├─────────────┼────────────────────┤
              │S/390        │               2 MB │
              ├─────────────┼────────────────────┤
              │Sparc-32     │               2 MB │
              ├─────────────┼────────────────────┤
              │Sparc-64     │               4 MB │
              ├─────────────┼────────────────────┤
              │x86_64       │               2 MB │
              └─────────────┴────────────────────┘