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#include <sys/file.h>
Advisory locks allow cooperating processes to perform consistent operations on files, but do not guarantee consistency (i.e., processes may still access files without using advisory locks possibly resulting in inconsistencies).
The locking mechanism allows two types of locks: shared locks and exclusive locks. At any time multiple shared locks may be applied to a file, but at no time are multiple exclusive, or both shared and exclusive, locks allowed simultaneously on a file.
A shared lock may be upgraded to an exclusive lock, and vice versa, simply by specifying the appropriate lock type; this results in the previous lock being released and the new lock applied (possibly after other processes have gained and released the lock).
Requesting a lock on an object that is already locked normally causes the caller to be blocked until the lock may be acquired. If LOCK_NB is included in operation, then this will not happen; instead the call will fail and the error EWOULDBLOCK will be returned.
The flock(), fcntl(2), and lockf(3) locks are compatible. Processes using different locking interfaces can cooperate over the same file safely. However, only one of such interfaces should be used within the same process. If a file is locked by a process through flock(), any record within the file will be seen as locked from the viewpoint of another process using fcntl(2) or lockf(3), and vice versa.
Processes blocked awaiting a lock may be awakened by signals.
[EWOULDBLOCK] | |
The file is locked and the LOCK_NB option was specified. | |
[EBADF] | |
The argument fd is an invalid descriptor. | |
[EINVAL] | |
The argument fd refers to an object other than a file. | |
[EOPNOTSUPP] | |
The argument fd refers to an object that does not support file locking. | |
[ENOLCK] | |
A lock was requested, but no locks are available. | |
FLOCK (2) | November 9, 2011 |
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