Waiting for semaphore to be created

[35053]

Why this message appear, what it means

98:00090 Waiting for semaphore to be
created...

 

[khalidaaa]

Hi 35053,

Sometimes a process may need to wait for some other process to finish before it can continue. In this instance, the two processes need to be synchronized together. There are a number of ways in which this can be done. A common method in operating systems is to use a variable called a semaphore that only one process can own at a time. There are two calls associated with a semaphore, one to lock it and one to unlock it. When a process attempts to lock a semaphore, it will be successful if the semaphore is free. If the semaphore is already locked, the process requesting the lock will be blocked and remain blocked till the process that has the semaphore unlocks it. When that happens, the process that was blocked will be unblocked and the semaphore can then be locked by it.

System semaphores are used by the operating system to control system resources. A program can be assigned a resource by getting a semaphore (via a system call to the operating system). When the resource is no longer needed, the semaphore is returned to the operating system, which can then allocate it to another program.

http://www4.dogus.edu.tr/bim/bil_kay/genel/selfstudy/opsys/os03.htm

http://www-128.ibm.com/developerworks/eserver/library/es-win32linux-sem.html

Regards,
Khalid