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General Programming Concepts: Writing and Debugging Programs

Threads Library Quick Reference

This section provides a summary of the threads library:

Supported Interfaces

On AIX systems, _POSIX_THREADS, _POSIX_THREAD_ATTR_STACKADDR, _POSIX_THREAD_ATTR_STACKSIZE and _POSIX_THREAD_PROCESS_SHARED are always defined. Therefore, the following threads interfaces are supported:

POSIX Interfaces

pthread_atfork pthread_attr_destroy
pthread_attr_getdetachstate pthread_attr_getschedparam
pthread_attr_getstackaddr pthread_attr_getstacksize
pthread_attr_init pthread_attr_setdetachstate
pthread_attr_setschedparam pthread_attr_setstackaddr
pthread_attr_setstacksize pthread_cancel
pthread_cleanup_pop pthread_cleanup_push
pthread_detach pthread_equal
pthread_exit pthread_getspecific
pthread_join pthread_key_create
pthread_key_delete pthread_kill
pthread_mutex_destroy pthread_mutex_init
pthread_mutex_lock pthread_mutex_trylock
pthread_mutex_unlock pthread_mutexattr_destroy
pthread_mutexattr_getpshared pthread_mutexattr_init
pthread_mutexattr_setpshared pthread_once
pthread_self pthread_setcancelstate
pthread_setcanceltype pthread_setspecific
pthread_sigmask pthread_testcancel
sigwait pthread_cond_broadcast
pthread_cond_destroy pthread_cond_init
pthread_cond_signal pthread_cond_timedwait
pthread_cond_wait pthread_condattr_destroy
pthread_condattr_getpshared pthread_condattr_init
pthread_condattr_setpshared pthread_create

Single Unix Specification Interfaces

pthread_attr_getguardsize pthread_attr_setguardsize
pthread_getconcurrency pthread_mutexattr_gettype
pthread_mutexattr_settype pthread_rwlock_destroy
pthread_rwlock_init pthread_rwlock_rdlock
pthread_rwlock_tryrdlock pthread_rwlock_trywrlock
pthread_rwlock_unlock pthread_rwlock_wrlock
pthread_rwlockattr_destroy pthread_rwlockattr_getpshared
pthread_rwlockattr_init pthread_rwlockattr_setpshared
pthread_setconcurrency

On AIX systems, _POSIX_THREAD_SAFE_FUNCTIONS is always defined. Therefore, the following interfaces are always supported:

asctime_r ctime_r
flockfile ftrylockfile
funlockfile getc_unlocked
getchar_unlocked getgrgid_r
getgrnam_r getpwnam_r
getpwuid_r gmtime_r
localtime_r putc_unlocked
putchar_unlocked rand_r
readdir_r strtok_r

AIX does not support the following interfaces; the symbols are provided but they always return an error and set the errno to ENOSYS:

pthread_attr_getinheritsched pthread_attr_getschedpolicy
pthread_attr_getscope pthread_attr_setinheritsched
pthread_attr_setschedpolicy pthread_attr_setscope
pthread_getschedparam pthread_mutex_getprioceiling
pthread_mutex_setprioceiling pthread_mutexattr_getprioceiling
pthread_mutexattr_getprotocol pthread_mutexattr_setprioceiling
pthread_mutexattr_setprotocol pthread_setschedparam

Thread-safety

The following AIX interfaces are not thread-safe.

libc.a Library (Standard Functions):

advance asctime brk catgets
chroot compile ctime cuserid
dbm_clearerr dbm_close dbm_delete dbm_error
dbm_fetch dbm_firstkey dbm_nextkey dbm_open
dbm_store dirname drand48 ecvt
encrypt endgrent endpwent endutxent
fcvt gamma gcvt getc_unlocked
getchar_unlocked getdate getdtablesize getenv
getgrent getgrgid getgrnam getlogin
getopt getpagesize getpass getpwent
getpwnam getpwuid getutxent getutxid
getutxline getw getw gmtime
l64a lgamma localtime lrand48
mrand48 nl_langinfo ptsname putc_unlocked
putchar_unlocked putenv pututxline putw
rand random readdir re_comp
re_exec regcmp regex sbrk
setgrent setkey setlocale setpwent
setutxent sigstack srand48 srandom
step strerror strtok ttyname
ttyslot wait3    

libc.a Library (AIX Specific Functions):

endfsent endttyent endutent
getfsent getfsfile getfsspec
getfstype getttyent getttynam
getutent getutid getutline
pututline setfsent setttyent
setutent utmpname

libbsd.a library:

timezone

libm.a and libmsaa.a libraries:

gamma lgamma

None of the functions in the following libraries are thread safe:

The interfaces ctermid and tmpnam are not thread-safe if passed a NULL argument.

Note: Certain subroutines may be implemented as macros on some systems. You should avoid using the address of threads subroutines.

Threads Data Types

The following data types are defined for the threads library in the pthread.h header file.

pthread_t Identifies a thread.
pthread_attr_t Identifies a thread attributes object.
pthread_cond_t Identifies a condition variable.
pthread_condattr_t Identifies a condition attributes object.
pthread_key_t Identifies a thread-specific data key.
pthread_mutex_t Identifies a mutex.
pthread_mutexattr_t Identifies a mutex attributes object.
pthread_once_t Identifies a one time initialization object.

The definition of these data types may vary from one system to another.

Limits and Default Values

The threads library has some implementation-dependent limits and default values. These limits and default values can be retrieved by symbolic constants to enhance the portability of programs.

Maximum Number of Threads per Process

The maximum number of threads per process is 512. The maximum number of threads can be retrieved at compilation time using the PTHREAD_THREADS_MAX symbolic constant defined in the pthread.h header file.

Minimum Stack Size

The minimum stack size for a thread is 96KB. It is also the default stack size. This number can be retrieved at compilation time using the PTHREAD_STACK_MIN symbolic constant defined in the pthread.h header file.

Note that the maximum stack size is 256MB, the size of a segment. This limit is indicated by the PTHREAD_STACK_MAX symbolic constant in the pthread.h header file.

Maximum Number of Thread-Specific Data Keys

The number of thread-specific data keys is limited to 508. This number can be retrieved at compilation time using the PTHREAD_KEYS_MAX symbolic constant defined in the pthread.h header file.

Default Attribute Values

The default values for the thread attributes object are defined in the pthread.h header file by the following symbolic constants:

DEFAULT_DETACHSTATE PTHREAD_CREATE_DETACHED. Specifies the default value for the detachstate attribute.
DEFAULT_INHERIT PTHREAD_INHERIT_SCHED. Specifies the default value for the inheritsched attribute.
DEFAULT_PRIO 1 (one). Specifies the default value for the sched_prio field of the schedparam attribute.
DEFAULT_SCHED SCHED_OTHER. Specifies the default value for the schedpolicy attribute of a thread attributes object.
DEFAULT_SCOPE PTHREAD_SCOPE_LOCAL. Specifies the default value for the contention-scope attribute.

The actual values shown may vary from one release to another.

Related Information

Threads Programming Overview.

Threads Library Options.

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