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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)
- semaphores
cc [flag... ]file... -lthread –lc [library... ]#include <synch.h>intsema_init(sema_t *sp,unsigned intcount,inttype,void *arg);
intsema_destroy(sema_t *sp);
intsema_wait(sema_t *sp);
intsema_trywait(sema_t *sp);
intsema_post(sema_t *sp);
A semaphore is a non-negative integer count and is generally used tocoordinate access to resources. The initial semaphore count is set to thenumber of free resources, then threads slowly increment and decrement the countas resources are added and removed. If the semaphore count drops to0, which means no available resources, threads attempting to decrement thesemaphore will block until the count is greater than 0.
Semaphores can synchronize threads in this process and other processes if theyare allocated in writable memory and shared among the cooperating processes(seemmap(2)), and have been initialized for this purpose.
Semaphores must be initialized before use; semaphores pointed to bysp tocount are initialized bysema_init(). Thetype argument can assign several differenttypes of behavior to a semaphore. No current type usesarg, although itmay be used in the future.
Thetype argument may be one of the following:
The semaphore can synchronize threads in this process and other processes. Initializing the semaphore should be done by only one process. A semaphore initialized with this type must be allocated in memory shared between processes, either in Sys V shared memory (seeshmop(2)), or in memory mapped to a file (seemmap(2)). It is illegal to initialize the object this way and not allocate it in such shared memory.arg is ignored.
The semaphore can synchronize threads only in this process. Thearg argument is ignored.USYNC_THREAD does not support multiple mappings to the same logical synch object. If you need tommap() a synch object to different locations within the same address space, then the synch object should be initialized as a shared objectUSYNC_PROCESS for Solaris threads andPTHREAD_PROCESS_PRIVATE for POSIX threads.
A semaphore must not be simultaneously initialized by multiple threads, nor re-initializedwhile in use by other threads.
Default semaphore initialization (intra-process):
sema_t sp;int count = 1;sema_init(&sp, count, NULL, NULL);
or
sema_init(&sp, count, USYNC_THREAD, NULL);
Customized semaphore initialization (inter-process):
sema_t sp;int count = 1;sema_init(&sp, count, USYNC_PROCESS, NULL);
Thesema_destroy() function destroys any state related to the semaphore pointed tobysp. The semaphore storage space is not released.
Thesema_wait() function blocks the calling thread until the semaphore count pointedto bysp is greater than 0, and then it atomically decrementsthe count.
Thesema_trywait() function atomically decrements the semaphore count pointed to bysp,if the count is greater than 0; otherwise, it returns an error.
Thesema_post() function atomically increments the semaphore count pointed to bysp.If there are any threads blocked on the semaphore, one will beunblocked.
The semaphore functionality described on this man page is for the Solaristhreads implementation. For the POSIX-conforming semaphore interface documentation, seesem_close(3C),sem_destroy(3C),sem_getvalue(3C),sem_init(3C),sem_open(3C),sem_post(3C),sem_unlink(3C), andsem_wait(3C).
Upon successful completion,0 is returned; otherwise, a non-zero value indicatesan error.
These functions will fail if:
Thesp argument does not refer to a valid semaphore.
Either thesp orarg argument points to an illegal address.
Thesema_wait() function will fail if:
The wait was interrupted by a signal orfork().
Thesema_trywait() function will fail if:
The semaphore pointed to bysp has a 0 count.
Thesema_post() function will fail if:
The semaphore value pointed to bysp exceedsSEM_VALUE_MAX.
Example 1 The customer waiting-line in a bank is analogous to the synchronization scheme of a semaphore usingsema_wait() andsema_trywait():
/* cc [ flag . . . ] file . . . –lthread [ library . . . ] */#include <errno.h>#define TELLERS 10sema_t tellers; /* semaphore */int banking_hours(), deposit_withdrawal;void*customer(), do_business(), skip_banking_today();. . .sema_init(&tellers, TELLERS, USYNC_THREAD, NULL); /* 10 tellers available */while(banking_hours()) pthread_create(NULL, NULL, customer, deposit_withdrawal);. . .void *customer(int deposit_withdrawal){ int this_customer, in_a_hurry = 50; this_customer = rand() % 100; if (this_customer == in_a_hurry) { if (sema_trywait(&tellers) != 0) if (errno == EBUSY){ /* no teller available */ skip_banking_today(this_customer); return; } /* else go immediately to available teller and decrement tellers */ } else sema_wait(&tellers); /* wait for next teller, then proceed, and decrement tellers */ do_business(deposit_withdrawal); sema_post(&tellers); /* increment tellers; this_customer's teller is now available */}Seeattributes(5) for descriptions of the following attributes:
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mmap(2),shmop(2),sem_close(3C),sem_destroy(3C),sem_getvalue(3C),sem_init(3C),sem_open(3C),sem_post(3C),sem_unlink(3C),sem_wait(3C),attributes(5),standards(5)
These functions are also available by way of:
#include <thread.h>
By default, there is no defined order of unblocking for multiple threadswaiting for a semaphore.
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