metrics = require('./Metrics') Settings = require('settings-sharelatex') redis = require("redis-sharelatex") rclient = redis.createClient(Settings.redis.web) keys = require('./RedisKeyBuilder') logger = require "logger-sharelatex" os = require "os" crypto = require "crypto" HOST = os.hostname() PID = process.pid RND = crypto.randomBytes(4).toString('hex') COUNT = 0 module.exports = LockManager = LOCK_TEST_INTERVAL: 50 # 50ms between each test of the lock MAX_LOCK_WAIT_TIME: 10000 # 10s maximum time to spend trying to get the lock LOCK_TTL: 30 # seconds. Time until lock auto expires in redis. # Use a signed lock value as described in # http://redis.io/topics/distlock#correct-implementation-with-a-single-instance # to prevent accidental unlocking by multiple processes randomLock : () -> time = Date.now() return "locked:host=#{HOST}:pid=#{PID}:random=#{RND}:time=#{time}:count=#{COUNT++}" unlockScript: 'if redis.call("get", KEYS[1]) == ARGV[1] then return redis.call("del", KEYS[1]) else return 0 end'; tryLock : (doc_id, callback = (err, isFree)->)-> lockValue = LockManager.randomLock() key = keys.blockingKey(doc_id:doc_id) rclient.set key, lockValue, "EX", @LOCK_TTL, "NX", (err, gotLock)-> return callback(err) if err? if gotLock == "OK" metrics.inc "doc-not-blocking" callback err, true, lockValue else metrics.inc "doc-blocking" logger.log {doc_id}, "doc is locked" callback err, false getLock: (doc_id, callback = (error) ->) -> startTime = Date.now() do attempt = () -> if Date.now() - startTime > LockManager.MAX_LOCK_WAIT_TIME e = new Error("Timeout") e.doc_id = doc_id return callback(e) LockManager.tryLock doc_id, (error, gotLock, lockValue) -> return callback(error) if error? if gotLock callback(null, lockValue) else setTimeout attempt, LockManager.LOCK_TEST_INTERVAL checkLock: (doc_id, callback = (err, isFree)->)-> key = keys.blockingKey(doc_id:doc_id) rclient.exists key, (err, exists) -> return callback(err) if err? exists = parseInt exists if exists == 1 metrics.inc "doc-blocking" callback err, false else metrics.inc "doc-not-blocking" callback err, true releaseLock: (doc_id, lockValue, callback)-> key = keys.blockingKey(doc_id:doc_id) rclient.eval LockManager.unlockScript, 1, key, lockValue, callback