FLOCKFILE(3) BSD Library Functions Manual FLOCKFILE(3)NAME
flockfile, ftrylockfile, funlockfile — stdio locking functions
Standard C Library (libc, -lc)
These functions provide explicit application-level locking of stdio
streams. They can be used to avoid output from multiple threads being
interspersed, input being dispersed among multiple readers, and to avoid
the overhead of locking the stream for each operation.
The flockfile() function acquires an exclusive lock on the specified
stream. If another thread has already locked the stream, flockfile()
will block until the lock is released.
The ftrylockfile() function is a non-blocking version of flockfile(); if
the lock cannot be acquired immediately, ftrylockfile() returns non-zero
instead of blocking.
The funlockfile() function releases the lock on a stream acquired by an
earlier call to flockfile() or ftrylockfile().
These functions behave as if there is a lock count associated with each
stream. Each time flockfile() is called on the stream, the count is
incremented, and each time funlockfile() is called on the stream, the
count is decremented. The lock is only actually released when the count
The flockfile() and funlockfile() functions return no value.
The ftrylockfile() function returns zero if the stream was successfully
locked, non-zero otherwise.
SEE ALSOgetc_unlocked(3), putc_unlocked(3)STANDARDS
The flockfile(), ftrylockfile() and funlockfile() functions conform to
IEEE Std 1003.1-2001 (“POSIX.1”).
BSD January 10, 2003 BSD