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Diffstat (limited to 'common/lock.js')
| -rw-r--r-- | common/lock.js | 94 |
1 files changed, 0 insertions, 94 deletions
diff --git a/common/lock.js b/common/lock.js deleted file mode 100644 index f577481..0000000 --- a/common/lock.js +++ /dev/null @@ -1,94 +0,0 @@ -/** - * This file is part of Haketilo. - * - * Function: Implement a lock (aka binary semaphore aka mutex). - * - * Copyright (C) 2021 Wojtek Kosior - * - * This program is free software: you can redistribute it and/or modify - * it under the terms of the GNU General Public License as published by - * the Free Software Foundation, either version 3 of the License, or - * (at your option) any later version. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * As additional permission under GNU GPL version 3 section 7, you - * may distribute forms of that code without the copy of the GNU - * GPL normally required by section 4, provided you include this - * license notice and, in case of non-source distribution, a URL - * through which recipients can access the Corresponding Source. - * If you modify file(s) with this exception, you may extend this - * exception to your version of the file(s), but you are not - * obligated to do so. If you do not wish to do so, delete this - * exception statement from your version. - * - * As a special exception to the GPL, any HTML file which merely - * makes function calls to this code, and for that purpose - * includes it by reference shall be deemed a separate work for - * copyright law purposes. If you modify this code, you may extend - * this exception to your version of the code, but you are not - * obligated to do so. If you do not wish to do so, delete this - * exception statement from your version. - * - * You should have received a copy of the GNU General Public License - * along with this program. If not, see <https://www.gnu.org/licenses/>. - * - * I, Wojtek Kosior, thereby promise not to sue for violation of this file's - * license. Although I request that you do not make use of this code in a - * proprietary program, I am not going to enforce this in court. - */ - -/* - * Javascript runs single-threaded, with an event loop. Because of that, - * explicit synchronization is often not needed. An exception is when we use - * an API function that must wait. Ajax is an example. Callback passed to ajax - * call doesn't get called immediately, but after some time. In the meantime - * some other piece of code might get to execute and modify some variables. - * Access to WebExtension local storage is another situation where this problem - * can occur. - * - * This is a solution. A lock object, that can be used to delay execution of - * some code until other code finishes its critical work. Locking is wrapped - * in a promise. - */ - -#EXPORT () => ({free: true, queue: []}) AS make_lock - -function _lock(lock, cb) { - if (lock.free) { - lock.free = false; - setTimeout(cb); - } else { - lock.queue.push(cb); - } -} - -#EXPORT lock => new Promise(resolve => _lock(lock, resolve)) AS lock - -function try_lock(lock) -{ - if (lock.free) { - lock.free = false; - return true; - } - - return false; -} -#EXPORT try_lock - -function unlock(lock) { - if (lock.free) - throw new Exception("Attempting to release a free lock"); - - if (lock.queue.length === 0) { - lock.free = true; - } else { - let cb = lock.queue[0]; - lock.queue.splice(0, 1); - setTimeout(cb); - } -} -#EXPORT unlock |