void
flockfile(
FILE *file
)
int
ftrylockfile(
FILE *file
)
void
funlockfile(
FILE *file
)
),
ftrylockfile(
),
and
funlockfile(
)
functions provide applications with explicit control of locking of
stdio stream objects.
They can be used by a thread to execute a sequence of I/O operations
as a unit, without interference from another thread.
Locks on stdio streams are recursive, and a lock count is maintained. stdio streams are created unlocked, with a lock count of zero. After successful acquisition of the lock, its count is incremented to one, indicating locked state of the stdio stream. Each subsequent relock operation performed by the owner thread increments the lock count by one, and each subsequent unlock operation performed by the owner thread decrements the lock count by one, allowing matching lock and unlock operations to be nested. After its lock count is decremented to zero, the stdio stream returns to unlocked state, and ownership of the stdio stream is relinquished.
The
flockfile()
function acquires the ownership of
file
for the calling thread.
If
file
is already owned by another thread, the calling thread is suspended
until the acquisition is possible (i.e.,
file
is relinquished again and the calling thread is scheduled to acquire it).
The
ftrylockfile()
function acquires the ownership of
file
for the calling thread only if
file
is available.
The
funlockfile()
function relinquishes the ownership of
file
previously granted to the calling thread.
Only the current owner of
file
may
funlockfile()
it.
)
function returns 0.
Otherwise, it returns non-zero to indicate that the lock cannot be acquired.
),
ftrylockfile(
)
and
funlockfile(
)
functions conform to
IEEE Std 1003.1-2001 (``POSIX.1'') .