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<?php
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+/***************************************************************************
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+ * This gives a method of mutual exclusion for critical Sections within
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+ * your script. A lock-file will be created for every critical section that
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+ * must be secured. The file hold information about the lock and is a
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+ * handle (name) for the lock, so that every script uses the same lock.
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+ * The lock will be achieved by one of two ways.
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+ *
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+ * 1. by using semaphores if they are available within the current php
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+ * installation.
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+ * 2. else by using flock, which exists within every php installation.
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+ *
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+ * Semaphores are used in favour because flock did not work reliably in
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+ * threaded environments. That means, if we have no semaphores and are
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+ * in a threaded environment these functions are also not reliable.
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+ * In doubt ask your administrator or provider.
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+ *
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+ * Author: Georg Steffers <georg@steffers.org
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+ * Date: 14th Oct. 2007
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+ ***************************************************************************/
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require_once dirname(__FILE__) . '/../config.php';
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require_once LIBDIR . 'errException.php';
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-
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-function acquireLock ($lockFile, $csId)
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+/**
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+ * Try to acquire a lock to enter a critical section. If the lock is already
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+ * acquired the function blocks until the lock id freed again. If more than
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+ * one process waits for the lock, than it is undefined which process get
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+ * the lock next. This depends on which process gets CPU time first. All other
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+ * processes continue waiting.
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+ *
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+ * Sideeffects:
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+ * If this function succeeds ignore_user_abort is set to TRUE so that the
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+ * critical section might not be interruped by a user abort. This can
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+ * but shouldn't be changed within the critical section and will be reset
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+ * in releaseLock.
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+ *
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+ * Arguments:
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+ * $lockFile <string>: Path and basename to the lockfile to use.
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+ * $csId <string[1]>: Id of the critical section, will be part of filename.
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+ * $msg <string>: The message to be written to the lockfile.
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+ *
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+ * If $msg is NULL, a default message is created from session_id and time
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+ *
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+ * Returns:
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+ * Array of lock information.
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+ * [0] Filehandle to opened lockfile.
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+ * [1] Resource id for semaphor
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+ * [2] the old setting of ignore_user_abort.
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+ */
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+function acquireLock ($lockFile, $csId, $msg = NULL)
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{
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$fName = $lockFile . $csId . '.lck';
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$lock = NULL;
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...
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...
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@@ -31,7 +75,9 @@ function acquireLock ($lockFile, $csId) |
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}
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// Here one could write informations in the lockfile...time, pid, etc.
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- fwrite ($lockHandle, session_id () . '::' . time ());
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+ if ($msg === NULL)
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+ $msg = session_id () . '::' . time ();
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+ fwrite ($lockHandle, $msg . "\n");
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fflush ($lockHandle);
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resetErrExceptionMapping ();
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...
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...
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@@ -40,6 +86,15 @@ function acquireLock ($lockFile, $csId) |
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return array ($lockHandle, $lock, $userAbort);
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}
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+/**
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+ * Release a lock previously acquired by acquireLock.
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+ *
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+ * Sideeffects:
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+ * Sets ignore_user_abort to the value before acquireLock succeds.
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+ *
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+ * Arguments:
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+ * $lock <array[3]>: The array returned by a successfull acquireLock call.
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+ */
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function releaseLock ($lock)
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{
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setErrExceptionMapping ();
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...
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...
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