Add actual locking and log changes necessary for debugging.

1 files changed, 242 insertions, 25 deletions

diff --git a/lib/public/files/lock.php b/lib/public/files/lock.php
index cc39e674b50..499957bd803 100644
--- a/lib/public/files/lock.php
+++ b/lib/public/files/lock.php
@@ -17,6 +17,8 @@
  */
 
 namespace OCP\Files;
+
+use OCP\Config;
 use OC\Files\Filesystem;
 
 /**
@@ -27,17 +29,26 @@ class Lock {
 	const READ = 1;
 	const WRITE = 2;
 
+	/** @var int $retries Number of lock retries to attempt */
+	public static $retries = 40;
+
+	/** @var int $retryInterval Milliseconds between retries */
+	public static $retryInterval = 50;
+
 	/** @var string $path Filename of the file as represented in storage */
 	protected $path;
 
 	/** @var array $stack A stack of lock data */
 	protected $stack = array();
 
-	/** @var int $retries Number of lock retries to attempt */
-	public static $retries = 40;
+	/** @var resource $handle A file handle used to maintain a lock  */
+	protected $handle;
 
-	/** @var int $retryInterval Milliseconds between retries */
-	public static $retryInterval = 50;
+	/** @var string $lockFile Filename of the lock file */
+	protected $lockFile;
+
+	/** @var resource $lockFileHandle The file handle used to maintain a lock on the lock file */
+	protected $lockFileHandle;
 
 	/**
 	 * Constructor for the lock instance
@@ -47,32 +58,160 @@ class Lock {
 		$this->path = Filesystem::normalizePath($path);
 	}
 
+	protected function obtainReadLock($existingHandle = null) {
+		\OC_Log::write('lock', sprintf('INFO: Read lock requested for %s', $this->path), \OC_Log::DEBUG);
+		$timeout = Lock::$retries;
+
+		// Re-use an existing handle or get a new one
+		if(empty($existingHandle)) {
+			$handle = fopen($this->path, 'r');
+		}
+		else {
+			$handle = $existingHandle;
+		}
+
+		do {
+			if($this->isLockFileLocked($this->getLockFile($this->path))) {
+				\OC_Log::write('lock', sprintf('INFO: Read lock has locked lock file %s for %s', $this->getLockFile($this->path), $this->path), \OC_Log::DEBUG);
+				do {
+					usleep(Lock::$retryInterval);
+					$timeout--;
+				} while($this->isLockFileLocked($this->getLockFile($this->path)) && $timeout > 0);
+				\OC_Log::write('lock', sprintf('INFO: Lock file %s has become unlocked for %s', $this->getLockFile($this->path), $this->path), \OC_Log::DEBUG);
+			}
+		} while ((!$lockReturn = flock($handle, LOCK_SH | LOCK_NB, $wouldBlock)) && $timeout > 0);
+		if ($wouldBlock == true || $lockReturn == false || $timeout <= 0) {
+			\OC_Log::write('lock', sprintf('FAIL: Failed to acquire read lock for %s', $this->path), \OC_Log::DEBUG);
+			return false;
+		}
+		$this->handle = $handle;
+		\OC_Log::write('lock', sprintf('PASS: Acquired read lock for %s', $this->path), \OC_Log::DEBUG);
+		return true;
+	}
+
+	protected function obtainWriteLock($existingHandle = null) {
+		\OC_Log::write('lock', sprintf('INFO: Write lock requested for %s', $this->path), \OC_Log::DEBUG);
+
+		// Re-use an existing handle or get a new one
+		if (empty($existingHandle)) {
+			$handle = fopen($this->path, 'c');
+		}
+		else {
+			$handle = $existingHandle;
+		}
+
+		// If the file doesn't exist, but we can create a lock for it
+		if (!file_exists($this->path) && $this->lockLockFile($this->path)) {
+			$lockReturn = flock($handle, LOCK_EX | LOCK_NB, $wouldBlock);
+			if ($lockReturn == false || $wouldBlock == true) {
+				\OC_Log::write('lock', sprintf('FAIL: Write lock failed, unable to exclusively lock new file %s', $this->path), \OC_Log::DEBUG);
+				return false;
+			}
+			$this->handle = $handle;
+			return true;
+		}
+
+
+		// Since this file does exist, wait for locks to release to get an exclusive lock
+		$timeout = Lock::$retries;
+		$haveBlock = false;
+		while ((!$lockReturn = flock($handle, LOCK_EX | LOCK_NB, $wouldBlock)) && $timeout > 0) {
+			// We don't have a lock on the original file, try to get a lock on its lock file
+			if ($haveBlock || $haveBlock = $this->lockLockFile($this->lockFile)) {
+				usleep(Lock::$retryInterval);
+			}
+			else {
+				\OC_Log::write('lock', sprintf('FAIL: Write lock failed, unable to lock original %s or lock file', $this->path), \OC_Log::DEBUG);
+				return false;
+			}
+			$timeout--;
+		}
+		if ($wouldBlock == true || $lockReturn == false) {
+			\OC_Log::write('lock', sprintf('FAIL: Write lock failed due to timeout on %s', $this->path), \OC_Log::DEBUG);
+			return false;
+		}
+		\OC_Log::write('lock', sprintf('PASS: Write lock succeeded on %s', $this->path), \OC_Log::DEBUG);
+
+		return true;
+	}
+
 	/**
-	 * @param integer $lockType A constant representing the type of lock to queue
+	 * Create a lock file and lock it
+	 * Sets $this->lockFile to the specified lock file, indicating that the lock file is IN USE for this lock instance
+	 * Also sets $this->lockFileHandle to a file handle of the lock file
+	 * @param string $filename The name of the file to lock
+	 * @param int $timeout Milliseconds to wait for a valid lock
+	 * @return bool False if lock can't be acquired, true if it can.
 	 */
-	public function addLock($lockType) {
-		\OC_Log::write('lock', sprintf('INFO: Lock type %d requested for %s', $lockType, $this->path), \OC_Log::DEBUG);
+	protected function lockLockFile ( $filename, $timeout = 0 ) {
+		$lockFile = $this->getLockFile($filename);
+		\OC_Log::write('lock', sprintf('INFO: Locking lock file %s for %s', $lockFile, $filename), \OC_Log::DEBUG);
+
+		// If we already manage the lockfile, success
+		if(!empty($this->lockFile)) {
+			\OC_Log::write('lock', sprintf('PASS: Lock file %s was locked by this request for %s', $lockFile, $filename), \OC_Log::DEBUG);
+			return true;
+		}
+
+		// Check if the lockfile exists, and if not, try to create it
+		\OC_Log::write('lock', sprintf('INFO: Does lock file %s already exist?  %s', $lockFile, file_exists($lockFile) ? 'yes' : 'no'), \OC_Log::DEBUG);
+		$handle = fopen($lockFile, 'c');
+		if(!$handle) {
+			\OC_Log::write('lock', sprintf('FAIL: Could not create lock file %s', $lockFile), \OC_Log::DEBUG);
+			return false;
+		}
+
+		// Attempt to acquire lock on lock file
+		$wouldBlock = false;
 		$timeout = self::$retries;
+		// Wait for lock over timeout
+		while((!$lockReturn = flock($handle, LOCK_EX | LOCK_NB, $wouldBlock)) && $timeout > 0) {
+			\OC_Log::write('lock', sprintf('FAIL: Could not acquire lock on lock file %s, %s timeout increments remain.', $lockFile, $timeout), \OC_Log::DEBUG);
+			usleep(self::$retryInterval);
+			$timeout--;
+		}
+		if ($wouldBlock == true || $lockReturn == false) {
+			\OC_Log::write('lock', sprintf('FAIL: Could not acquire lock on lock file %s', $lockFile), \OC_Log::DEBUG);
+			return false;
+		}
+		fwrite($handle, $filename);
+		\OC_Log::write('lock', sprintf('PASS: Wrote filename to lock lock file %s', $lockFile), \OC_Log::DEBUG);
+
+		$this->lockFile = $lockFile;
+		$this->lockFileHandle = $handle;
+
+		return true;
+	}
 
+	/**
+	 * Add a lock of a specific type to the stack
+	 * @param integer $lockType A constant representing the type of lock to queue
+	 * @param null|resource $existingHandle An existing file handle from an fopen()
+	 * @throws LockNotAcquiredException
+	 */
+	public function addLock($lockType, $existingHandle = null) {
 		if(!isset($this->stack[$lockType])) {
-			// does lockfile exist?
-				// yes
-				// Acquire exclusive lock on lockfile?
-					// yes
-					// Delete lockfile, release lock
-					// no
-					// Sleep for configurable milliseconds - start over
-				// no
-				// Acquire shared lock on original file?
-					// yes
-					// Capture handle, return for action
-					// no
-					// Sleep for configurable milliseconds - start over
-			$handle = 1;
-
-			$this->stack[$lockType] = array('handle' => $handle, 'count' => 0);
-		}
-		$this->stack[$lockType]['count']++;
+			switch($lockType) {
+				case Lock::READ:
+					$result = $this->obtainReadLock($existingHandle);
+					break;
+				case Lock::WRITE:
+					$result = $this->obtainWriteLock($existingHandle);
+					break;
+				default:
+					$result = false;
+					break;
+			}
+			if($result) {
+				$this->stack[$lockType] = 0;
+			}
+			else {
+				throw new LockNotAcquiredException($this->path, $lockType);
+			}
+		}
+
+		\OC_Log::write('lock', sprintf('INFO: Incrementing lock type %d count for %s', $lockType, $this->path), \OC_Log::DEBUG);
+		$this->stack[$lockType]++;
 
 	}
 
@@ -80,15 +219,93 @@ class Lock {
 	 * Release locks on handles and files
 	 */
 	public function release($lockType) {
+		if(isset($this->stack[$lockType])) {
+			$this->stack[$lockType]--;
+			if($this->stack[$lockType] <= 0) {
+				unset($this->stack[$lockType]);
+			}
+		}
+
+		if(count($this->stack) == 0) {
+			// No more locks needed on this file, release the handle and/or lockfile
+			$this->releaseAll();
+		}
+
 		return true;
 	}
 
+
+	/**
+	 * Get the lock file associated to a file
+	 * @param string $filename The filename of the file to create a lock file for
+	 * @return string The filename of the lock file
+	 */
+	public static function getLockFile($filename) {
+		static $locksDir = false;
+		if(!$locksDir) {
+			$dataDir = Config::getSystemValue('datadirectory');
+			$locksDir = $dataDir . '/.locks';
+			if(!file_exists($locksDir)) {
+				mkdir($locksDir);
+			}
+		}
+		$filename = Filesystem::normalizePath($filename);
+		return $locksDir . '/' . sha1($filename) . '.lock';
+	}
+
+	/**
+	 * Determine if a file has an associated and flocked lock file
+	 * @param string $lockFile The filename of the lock file to check
+	 * @return bool True if the lock file is flocked
+	 */
+	protected function isLockFileLocked($lockFile) {
+		if(file_exists($lockFile)) {
+			if($handle = fopen($lockFile, 'c')) {
+				if($lock = flock($handle, LOCK_EX | LOCK_NB)) {
+					// Got lock, not blocking, release and unlink
+					unlink($lockFile);
+					fclose($handle);
+					flock($lock, LOCK_UN);
+					return false;
+				}
+				else {
+					return true;
+				}
+			}
+			else {
+				return true;
+			}
+		}
+		return false;
+	}
+
 	/**
 	 * Release all queued locks on the file
 	 * @return bool
 	 */
 	public function releaseAll() {
+		$this->stack = array();
+		\OC_Log::write('lock', sprintf('INFO: Releasing locks on %s', $this->path), \OC_Log::DEBUG);
+		if (!empty($this->handle) && is_resource($this->handle)) {
+			flock($this->handle, LOCK_UN);
+			\OC_Log::write('lock', sprintf('INFO: Released lock handle %s on %s', $this->handle, $this->path), \OC_Log::DEBUG);
+			$this->handle = null;
+		}
+		if (!empty($this->lockFile) && file_exists($this->lockFile)) {
+			unlink($this->lockFile);
+			\OC_Log::write('lock', sprintf('INFO: Released lock file %s on %s', $this->lockFile, $this->path), \OC_Log::DEBUG);
+			$this->lockFile = null;
+		}
+		\OC_Log::write('lock', sprintf('FREE: Released locks on %s', $this->path), \OC_Log::DEBUG);
 		return true;
 	}
 
+	public function __destruct() {
+		// Only releaseAll if we have locks to release
+		if(!empty($this->handle) || !empty($this->lockFile)) {
+			\OC_Log::write('lock', sprintf('INFO: Destroying locks on %s', $this->path), \OC_Log::DEBUG);
+			$this->releaseAll();
+		}
+	}
+
 }
\ No newline at end of file