Initial file locking library for JS

exec/load/lockfile.js

+// lockfile.js
+
+// File locking library for JS
+
+// $Id$
+
+// @format.tab-size 4, @format.use-tabs true
+
+var LockedFiles=new Object();
+js.on_exit("UnlockAll()");
+
+function Lock(filename, lockid, forwrite, timeout)
+{
+	var readlock=new File(filename+".lock."+lockid);
+	var writelock=new File(filename+".lock");
+	var endtime=system.timer+timeout;
+
+	/* Do we already hold a lock on this file? */
+	if(LockedFiles[filename] != undefined) {
+		/* do we hold THIS lock on this file? */
+		if(LockedFiles[filename].lockid == lockid) {
+			if(LockedFiles[filename].forwrite == forwrite)
+				return(true);
+			/*
+			 * We currently hold a write lock and are requesting a read lock...
+			 */
+			if(forwrite==false) {
+				if(readlock.open("we")) {
+					readlock.close();
+					LockedFiles[filename].forwrite==false;
+					file_remote(writelock.name);
+				}
+				else {
+					log(LOG_ERROR, "!LOCK ERROR! -- cannot read lock a file we have write locked!");
+					return(false);
+				}
+			}
+			else {
+				/* We want to upgrade a read lock to a write lock... */
+			}
+		}
+		else {
+			/* We currently hold some other lock on this file.  As a result, we CANNOT relock with a different ID */
+			log(LOG_WARNING, "!LOCK ERROR! -- attempt to lock "+filename+" with ID '"+lockid+"' while we hold a lock with ID '"+LockedFiles[filename].lockid+"'");
+			return(false);
+		}
+	}
+
+	while(system.timer <= endtime) {
+		/* No lock can be created when there is a write lock */
+		if(!file_exists(filename+".lock")) {
+			if(forwrite) {
+				/* We are locking for write... attempt to create write lock file */
+				if(writelock.open("we")) {
+					writelock.close();
+					/* If we are upgading from a read lock, delete our read lock */
+					if(LockedFiles[filename]!=undefined)
+						file_remove(readlock.name);
+					/* We have got the lock... wait for all read locks to close */
+					while(directory(filename+".lock.*").length) {
+						mswait(1);
+						if(system.timer > endtime) {
+							/* If we were upgrading, restor our old lock... */
+							if(LockedFiles[filename]!=undefined) {
+								if(readlock.open("we")) {
+									readlock.close();
+								}
+							}
+							file_remove(writelock.name);
+							return(false);
+						}
+					}
+					LockedFiles[filename]=new Object();
+					LockedFiles[filename].forwrite=true;
+					LockedFiles[filename].lockid=lockid;
+					return(true);
+				}
+			}
+			else {
+				if(readlock.open("we")) {
+					readlock.close();
+					LockedFiles[filename]=new Object();
+					LockedFiles[filename].forwrite=false;
+					LockedFiles[filename].lockid=lockid;
+					return(true);
+				}
+			}
+		}
+		mswait(1);
+	}
+
+	return(false);
+}
+
+function Unlock(filename)
+{
+	var readlock;
+	var writelock=new File(filename+".lock");
+
+	if(LockedFiles[filename]==undefined)
+		return;
+	readlock=new File(filename+".lock."+LockedFiles[filename].lockid);
+
+	if(LockedFiles[filename].forwrite)
+		file_remove(writelock.name);
+	else
+		file_remove(readlock.name);
+
+	delete LockedFiles[filename];
+}
+
+function UnlockAll()
+{
+	for(filename in LockedFiles) {
+		Unlock(filename);
+	}
+}