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 | man pages section 3: Basic Library Functions Oracle Solaris 11 Information Library |
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| man pages section 3: Basic Library Functions Oracle Solaris 11 Information Library |
enable_extended_FILE_stdio(3C)
posix_spawnattr_getschedparam(3C)
posix_spawnattr_getschedpolicy(3C)
posix_spawnattr_getsigdefault(3C)
posix_spawnattr_getsigignore_np(3C)
posix_spawnattr_getsigmask(3C)
posix_spawnattr_setschedparam(3C)
posix_spawnattr_setschedpolicy(3C)
posix_spawnattr_setsigdefault(3C)
posix_spawnattr_setsigignore_np(3C)
posix_spawnattr_setsigmask(3C)
posix_spawn_file_actions_addclose(3C)
posix_spawn_file_actions_addclosefrom_np(3C)
posix_spawn_file_actions_adddup2(3C)
posix_spawn_file_actions_addopen(3C)
posix_spawn_file_actions_destroy(3C)
posix_spawn_file_actions_init(3C)
pthread_attr_getdetachstate(3C)
pthread_attr_getinheritsched(3C)
pthread_attr_getschedparam(3C)
pthread_attr_getschedpolicy(3C)
pthread_attr_setdetachstate(3C)
pthread_attr_setinheritsched(3C)
pthread_attr_setschedparam(3C)
pthread_attr_setschedpolicy(3C)
pthread_barrierattr_destroy(3C)
pthread_barrierattr_getpshared(3C)
pthread_barrierattr_setpshared(3C)
pthread_condattr_getpshared(3C)
pthread_condattr_setpshared(3C)
pthread_cond_reltimedwait_np(3C)
pthread_key_create_once_np(3C)
pthread_mutexattr_getprioceiling(3C)
pthread_mutexattr_getprotocol(3C)
pthread_mutexattr_getpshared(3C)
pthread_mutexattr_getrobust(3C)
pthread_mutexattr_setprioceiling(3C)
pthread_mutexattr_setprotocol(3C)
pthread_mutexattr_setpshared(3C)
pthread_mutexattr_setrobust(3C)
pthread_mutex_getprioceiling(3C)
pthread_mutex_reltimedlock_np(3C)
pthread_mutex_setprioceiling(3C)
pthread_rwlockattr_destroy(3C)
pthread_rwlockattr_getpshared(3C)
pthread_rwlockattr_setpshared(3C)
pthread_rwlock_reltimedrdlock_np(3C)
pthread_rwlock_reltimedwrlock_np(3C)
pthread_rwlock_timedrdlock(3C)
pthread_rwlock_timedwrlock(3C)
rctlblk_get_enforced_value(3C)
- acquire or wait for a semaphore
#include <semaphore.h>intsem_wait(sem_t *sem);
intsem_trywait(sem_t *sem);
Thesem_wait() function locks the semaphore referenced bysem by performing asemaphore lock operation on that semaphore. If the semaphore value is currentlyzero, then the calling thread will not return from the calltosem_wait() until it either locks the semaphore or the call is interruptedby a signal. Thesem_trywait() function locks the semaphore referenced bysemonly if the semaphore is currently not locked; that is, if thesemaphore value is currently positive. Otherwise, it does not lock the semaphore.
Upon successful return, the state of the semaphore is locked and remainslocked until thesem_post(3C) function is executed and returns successfully.
Thesem_wait() function is interruptible by the delivery of a signal.
Thesem_wait() andsem_trywait() functions return0 if the calling processsuccessfully performed the semaphore lock operation on the semaphore designated bysem.If the call was unsuccessful, the state of the semaphore is unchanged, andthe function returns-1 and setserrno to indicate the error.
Thesem_wait() andsem_trywait() functions will fail if:
Thesem function does not refer to a valid semaphore.
Thesem_wait() andsem_trywait() functions are not supported by the system.
Thesem_trywait() function will fail if:
The semaphore was already locked, so it cannot be immediately locked by thesem_trywait() operation.
Thesem_wait() andsem_trywait() functions may fail if:
A deadlock condition was detected; that is, two separate processes are waiting for an available resource to be released via a semaphore "held" by the other process.
A signal interrupted this function.
Realtime applications may encounter priority inversion when using semaphores. The problem occurswhen a high priority thread “locks” (that is, waits on) a semaphorethat is about to be “unlocked” (that is, posted) by a lowpriority thread, but the low priority thread is preempted by a medium prioritythread. This scenario leads to priority inversion; a high priority thread isblocked by lower priority threads for an unlimited period of time. Duringsystem design, realtime programmers must take into account the possibility of thiskind of priority inversion. They can deal with it in a number ofways, such as by having critical sections that are guarded by semaphoresexecute at a high priority, so that a thread cannot be preemptedwhile executing in its critical section.
Example 1 The customer waiting-line in a bank may be analogous to the synchronization scheme of a semaphore utilizingsem_wait() andsem_trywait():
#include <errno.h>#define TELLERS 10sem_t bank_line; /* semaphore */int banking_hours(), deposit_withdrawal;void *customer(), do_business(), skip_banking_today();thread_t tid;... sem_init(&bank_line,TRUE,TELLERS); /* 10 tellers available */while(banking_hours()) thr_create(NULL, NULL, customer, (void *)deposit_withdrawal, THREAD_NEW_LWP, &tid);... void *customer(deposit_withdrawal)void *deposit_withdrawal;{ int this_customer, in_a_hurry = 50; this_customer = rand() % 100; if (this_customer == in_a_hurry) { if (sem_trywait(&bank_line) != 0) if (errno == EAGAIN) { /* no teller available */ skip_banking_today(this_customer); return; } /*else go immediately to available teller & decrement bank_line*/ } else sem_wait(&bank_line); /* wait for next teller, then proceed, and decrement bank_line */ do_business((int *)deposit_withdrawal); sem_getvalue(&bank_line,&num_tellers); sem_post(&bank_line); /* increment bank_line; this_customer's teller is now available */}Seeattributes(5) for descriptions of the following attributes:
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