Linux and UNIX Man Pages

Test Your Knowledge in Computers #589
Difficulty: Medium
A binary search algorithm requires that the array being searched is sorted in descending order.
True or False?
Linux & Unix Commands - Search Man Pages

sem_trywait(2) [osx man page]

SEM_WAIT(2)						      BSD System Calls Manual						       SEM_WAIT(2)

NAME
sem_trywait, sem_wait -- lock a semaphore SYNOPSIS
#include <semaphore.h> int sem_trywait(sem_t *sem); int sem_wait(sem_t *sem); DESCRIPTION
The semaphore referenced by sem is locked. When calling sem_wait(), if the semaphore's value is zero, the calling thread will block until the lock is acquired or until the call is interrupted by a signal. Alternatively, the sem_trywait() function will fail if the semaphore is already locked, rather than blocking on the semaphore. If successful (the lock was acquired), sem_wait() and sem_trywait() will return 0. Otherwise, -1 is returned and errno is set, and the state of the semaphore is unchanged. ERRORS
sem_wait() and sem_trywait() succeed unless: [EAGAIN] The semaphore is already locked. [EDEADLK] A deadlock was detected. [EINTR] The call was interrupted by a signal. [EINVAL] sem is not a valid semaphore descriptor. NOTES
Applications may encounter a priority inversion while using semaphores. When a thread is waiting on a semaphore which is about to be posted by a lower-priority thread and the lower-priority thread is preempted by another thread (of medium priority), a priority inversion has occured, and the higher-priority thread will be blocked for an unlimited time period. Programmers using the realtime functionality of the system should take care to avoid priority inversions. SEE ALSO
sem_open(2), sem_post(2), semctl(2), semget(2), semop(2) HISTORY
sem_wait() and sem_trywait() are specified in the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995). Darwin June 8, 2000 Darwin

Check Out this Related Man Page

sem_wait(3)						     Library Functions Manual						       sem_wait(3)

NAME
sem_wait, sem_trywait - Performs (or conditionally performs) a semaphore lock (P1003.1b) LIBRARY
Realtime Library (librt.so, librt.a) SYNOPSIS
#include <semaphore.h> int sem_wait ( sem_t *sem); int sem_trywait ( sem_t *sem); PARAMETERS
sem Specifies a pointer to the semaphore to be locked. DESCRIPTION
The sem_wait function locks the semaphore referenced by sem by performing a semaphore lock operation on it. If the semaphore value is zero, the sem_wait function blocks until it either locks the semaphore or is interrupted by a signal. The sem_trywait function locks a semaphore only if the semaphore is currently not locked. If the semaphore value is zero, the sem_trywait function returns without locking the semaphore. These functions help ensure that the resource associated with the semaphore cannot be accessed by other processes. The semaphore remains locked until the process unlocks it with a call to the sem_post function. Use the sem_wait function instead of the sem_trywait function if the process should wait for access to the semaphore. RETURN VALUES
If the sem_wait or sem_trywait function returns successfully, a value of 0 (zero) is returned and the function executes the semaphore lock operation. On an unsuccessful call, a value of -1 is returned and errno is set to indicate that an error occurred. The state of the semaphore remains unchanged. ERRORS
The sem_wait and sem_trywait functions fail under the following conditions: [EAGAIN] The semaphore was already locked and cannot be locked by the sem_trywait operation (sem_trywait only). [EINTR] A signal interrupted this function. [EINVAL] The sem argument does not refer to a valid semaphore. RELATED INFORMATION
Functions: sem_post(3) Guide to Realtime Programming delim off sem_wait(3)

5 More Discussions You Might Find Interesting

1. Post Here to Contact Site Administrators and Moderators

Homework Issues

I think we need need to discuss the homework rules a little... In this thread, Neo is concerned that I may have helped someone with homework. I actually worried a little about that as I posted. But I decided that if a student was to turn in my script as his work, the instructor would probably... (11 Replies)
Discussion started by: Perderabo
11 Replies

2. Programming

semaphores

Hi there, Could someone please confirm which POSIX semaphore routines should be used for a multiprocess (and not multithreaded) environment? sys/sem.h definitely works. but the routines, semget, semctl, semop are pretty unwieldy. So, I am looking for an easier way out. From the man pages... (2 Replies)
Discussion started by: qntmteleporter
2 Replies

3. Programming

Semaphore debugging

I'm running one multithreaded application, in that one of my thread is waiting infinitely in a semphore. Is there a way to determine, in which semaphore the particular thread is waiting and which thread(s) is holding the semaphore. (5 Replies)
Discussion started by: ptprabu
5 Replies

4. HP-UX

avoid semphore lock

we developed a set of system V semphore interface for our application, in general, all of them work normal, seldom cause the deadlock. Here are some important sem_wait and sem_post interface, pls point some suggestion to fixed the deadlock problem: int sem_wait_V(int id, struct sembuf *sem_pv)... (1 Reply)
Discussion started by: Frank2004
1 Replies

5. Shell Programming and Scripting

Error

Can Someone help me what does the following error mean? ERR: 17-Oct-11 15:07:44: File etlDataLoad.c Line 1069: 895, A fatal error has occured. Posting semaphore information ERR: 17-Oct-11 15:07:44: File etlDataLoad.c Line 1174: 899, Local load partition 0 exited with a failure status of 256... (1 Reply)
Discussion started by: bobby1015
1 Replies

Featured Tech Videos