wincache_lock(3) [php man page]

WINCACHE_LOCK(3)							 1							  WINCACHE_LOCK(3)

wincache_lock - Acquires an exclusive lock on a given key

SYNOPSIS

       bool wincache_lock (string  $key, [bool	$isglobal = false])

DESCRIPTION

	Obtains  an  exclusive	lock  on a given key. The execution of the current script will be blocked until the lock can be obtained. Once the
       lock is obtained, the other scripts that try to request the lock by using the same key will be blocked, until the current  script  releases
       the lock by using wincache_unlock(3).

       Warning

	       Using  of the wincache_lock(3) and wincache_unlock(3) can cause deadlocks when executing PHP scripts in a multi-process environment
	      like FastCGI. Do not use these functions unless you are absolutely sure you need to use them. For the majority of the operations	on
	      the user cache it is not necessary to use these functions.

PARAMETERS

	      o $key
		- Name of the key in the cache to get the lock on.

	      o $isglobal
		-  Controls  whether  the scope of the lock is system-wide or local. Local locks are scoped to the application pool in IIS FastCGI
		case or to all php processes that have the same parent process identifier.

RETURN VALUES

	Returns TRUE on success or FALSE on failure.

EXAMPLES

       Example #1

	      Using wincache_lock(3)

	      <?php
	      $fp = fopen("/tmp/lock.txt", "r+");
	      if (wincache_lock("lock_txt_lock")) { // do an exclusive lock
		  ftruncate($fp, 0); // truncate file
		  fwrite($fp, "Write something here
");
		  wincache_unlock("lock_txt_lock"); // release the lock
	      } else {
		  echo "Couldn't get the lock!";
	      }
	      fclose($fp);
	      ?>

SEE ALSO

       wincache_unlock(3),   wincache_ucache_set(3),	wincache_ucache_get(3),    wincache_ucache_delete(3),	 wincache_ucache_clear(3),    win-
       cache_ucache_exists(3), wincache_ucache_meminfo(3), wincache_ucache_info(3), wincache_scache_info(3).

PHP Documentation Group 													  WINCACHE_LOCK(3)

flock(2)							System Calls Manual							  flock(2)

NAME

       flock - Applies or removes an advisory lock on an open file

SYNOPSIS

       #include <sys/fcntl.h>

       int flock(      int filedes,	 int operation );

PARAMETERS

       Specifies a file descriptor returned by a successful open() or fcntl() function, identifying the file to which the lock is to be applied or
       removed.  Specifies one of the following constants for flock(), defined in the fcntl.h file: Apply a shared lock.  Apply an exclusive lock.
       Do not block when locking. This value can be logically ORed with either LOCK_SH or LOCK_EX.  Remove a lock.

DESCRIPTION

       The  flock()  function  applies	or removes an advisory lock on the file associated with the filedes file descriptor.  Advisory locks allow
       cooperating processes to perform consistent operations on files, but do not guarantee consistency (that	is,  processes	may  still  access
       files without using advisory locks, possibly resulting in inconsistencies).

       You can use the flock() function to coordinate a file's lock status on local, CFS, and NFS file systems.

       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 errno will be set to [EWOULDBLOCK].

NOTES

       Locks are on files, not file descriptors.  That is, file descriptors duplicated using the dup() or fork() functions do not result in multi-
       ple  instances  of  a  lock,  but  rather  multiple references to a single lock.  If a process holding a lock on a file forks and the child
       explicitly unlocks the file, the parent will lose its lock.

       Processes blocked awaiting a lock may be awakened by signals.

       The flock() interface is not part of any UNIX standard.	Therefore, if you are designing and writing applications  to  be  portable  across
       platforms, you should use the fcntl() file locking interface instead of flock().

RETURN VALUES

       Upon successful completion, 0 (zero) is returned.  Otherwise, -1 is returned and errno is set to indicate the error.

ERRORS

       If  the	flock()  function fails, errno may be set to one of the following values: The file is locked and the LOCK_NB option was specified.
       The filedes argument is not a valid open file descriptor.  A signal interrupted the flock call.	The operator is not valid.  The lock table
       is  full.   Too	many  regions  are already locked.  The lock is blocked by some lock from another process.  Putting the calling process to
       sleep while waiting for that lock to become free would cause a deadlock.

RELATED INFORMATION

       Functions: close(2), exec(2), fcntl(2), fork(2), open(2), lockf(3) delim off

																	  flock(2)