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pthread_create(3) [osf1 man page]

pthread_create(3)					     Library Functions Manual						 pthread_create(3)

pthread_create - Creates a thread. LIBRARY
DECthreads POSIX 1003.1c Library ( SYNOPSIS
#include <pthread.h> int pthread_create( pthread_t *thread, const pthread_attr_t *attr, void * (*start_routine)(void *), void *arg); STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: IEEE Std 1003.1c-1995, POSIX System Application Program Interface PARAMETERS
Location for thread object to be created. Thread attributes object that defines the characteristics of the thread being created. If you specify NULL, default attributes are used. Function executed as the new thread's start routine. Address value copied and passed to the thread's start routine. DESCRIPTION
This routine creates a thread. A thread is a single, sequential flow of control within a program. It is the active execution of a desig- nated routine, including any nested routine invocations. Successful execution of this routine includes the following actions: DECthreads creates a thread object to describe and control the thread. The thread object includes a thread environment block (TEB) that programs can use, with care. (See the <sys/types.h> header file on Tru64 UNIX, or the pthread.h header file on other DECthreads platforms.) The thread argument receives an identifier for the new thread. An exe- cutable thread is created with attributes specified by the attr argument (or with default attributes if NULL is specified). Thread Creation DECthreads creates a thread in the "ready" state and prepares the thread to begin executing its start routine, the function passed to pthread_create(3) as the start_routine argument. Depending on the presence of other threads and their scheduling and priority attributes, the new thread might start executing immediately. The new thread can also preempt its creator, depending on the two threads' respective scheduling and priority attributes. The caller of pthread_create(3) can synchronize with the new thread using the pthread_join(3) routine or using any mutually agreed upon mutexes or condition variables. For the duration of the new thread's existence, DECthreads maintains and manages the thread object and other thread state overhead. A thread "exists" until it is both terminated and detached. A thread is detached when created if the detachstate attribute of its thread object is set to PTHREAD_CREATE_DETACHED. It is also detached after any thread returns successfully from calling pthread_detach(3) or pthread_join(3) for the thread. Termination is explained in the next section (see Thread Termination). DECthreads assigns each new thread a thread identifier, which DECthreads writes into the address specified as the pthread_create(3) rou- tine's thread argument. DECthreads writes the new thread's thread identifier before the new thread executes. By default, the new thread's scheduling policy and priority are inherited from the creating thread---that is, by default, the pthread_cre- ate(3) routine ignores the scheduling policy and priority set in the specified thread attributes object. Thus, to create a thread that is subject to the scheduling policy and priority set in the specified thread attributes object, before calling pthread_create(3) your program must use the pthread_attr_setinheritsched(3) routine to set the inherit thread attributes object's scheduling attribute to PTHREAD_EXPLICIT_SCHED. On Tru64 UNIX, the signal state of the new thread is initialized as follows: The signal mask is inherited from the creating thread. The set of signals pending for the new thread is empty. If pthread_create(3) fails, no new thread is created, and the contents of the location referenced by thread are undefined. Thread Termination A thread terminates when one of the following events occurs: The thread returns from its start routine. The thread calls the pthread_exit(3) routine. The thread is canceled. When a thread terminates, DECthreads performs these actions: DECthreads writes a return value (if one is available) into the terminated thread's thread object, as follows: If the thread has been canceled, DECthreads writes the value PTHREAD_CANCELED into the thread's thread object. If the thread terminated by returning from its start routine, DECthreads copies the return value from the start routine (if one is available) into the thread's thread object. Alternatively, if the thread explictly called pthread_exit(3), DECthreads stores the value received in the value_ptr argument (from pthread_exit(3)) into the thread's thread object. Another thread can obtain this return value by joining with the terminated thread (using pthread_join(3)). If the thread terminated by returning from its start routine normally and the start routine does not provide a return value, the results obtained by joining with that thread are unpredictable. If the termination results from a cancelation request or a call to pthread_exit(3), DECthreads calls, in turn, each cleanup handler that this thread declared (using pthread_cleanup_push(3)) and that is not yet removed (using pthread_cleanup_pop(3)). (DECthreads also transfers control to any appropriate CATCH, CATCH_ALL, or FINALLY blocks. DECthreads calls the terminated thread's most recently pushed cleanup handler first. For C++ programmers: At normal exit from a thread, your program will call the appropriate destructor functions, just as if an exception had been raised. To exit the terminated thread due to a call to pthread_exit(3), DECthreads raises the pthread_exit_e exception. To exit the terminated thread due to cancelation, DECthreads raises the pthread_cancel_e exception. Your program can use the DECthreads exception package to operate on the generated exception. (In particular, note that the practice of using CATCH handlers in place of pthread_cleanup_push(3) is not portable.) For each of the terminated thread's thread-specific data keys that has a non-NULL value: DEC- threads sets the thread's value for the corresponding key to NULL. In turn, DECthreads calls each thread-specific data destructor function in this multithreaded process's list of destructors. DECthreads repeats this step until all thread-specific data values in the thread are NULL, or for up to a number of iterations equal to PTHREAD_DESTRUCTOR_ITERATIONS. This destroys all thread-specific data associated with the terminated thread. DECthreads awakens the thread (if there is one) that is currently waiting to join with the terminated thread. That is, DECthreads awakens the thread that is waiting in a call to pthread_join(3). If the thread is already detached, DECthreads destroys its thread object. Otherwise, the thread continues to exist until detached or joined with. RETURN VALUES
If an error condition occurs, no thread is created, the contents of thread are undefined, and this routine returns an integer value indi- cating the type of error. Possible return values are as follows: Successful completion. The system lacks the necessary resources to cre- ate another thread, or the system-imposed limit on the total number of threads under execution by a single user is exceeded. The value specified by attr is invalid. Insufficient memory exists to create a thread. The caller does not have the appropriate permission to cre- ate a thread with the specified attributes. ERRORS
Functions: pthread_atfork(3), pthread_attr_destroy(3), pthread_attr_init(3), pthread_attr_setdetachstate(3), pthread_attr_setinher- itsched(3), pthread_attr_setschedparam(3), pthread_attr_setschedpolicy(3), pthread_attr_setstacksize(3), pthread_cancel(3), pthread_detach(3), pthread_exit(3), pthread_join(3) Manuals: Guide to DECthreads and Programmer's Guide delim off pthread_create(3)

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