NAME

opensem − open a semaphore

SYNOPSIS

cc [flag . . .] file . . . -lx
int opensem(char ∗sem_name);

DESCRIPTION

opensem opens a semaphore named by sem_name and returns the unique semaphore identification number sem_num used by waitsem and sigsem.  creatsem should always be called to initialize the semaphore before the first attempt to open it. 

DIAGNOSTICS

opensem returns a value of −1 if an error occurs.  If the semaphore named does not exist, errno is set to ENOENT.  If the file specified is not a semaphore file (that is, a file previously created by a process using a call to creatsem), errno is set to ENOTNAM.  If the semaphore has become invalid due to inappropriate use, errno is set to ENAVAIL. 

SEE ALSO

creatsem(2), sigsem(2), waitsem(2)

NOTES

It is not advisable to open the same semaphore more than once.  Although it is possible to do this, it may result in a deadlock. 

  —  Application Compatibility Package