mirror of
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86 lines
3.2 KiB
CoffeeScript
86 lines
3.2 KiB
CoffeeScript
metrics = require('./Metrics')
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Settings = require('settings-sharelatex')
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redis = require("redis-sharelatex")
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rclient = redis.createClient(Settings.redis.lock)
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keys = Settings.redis.lock.key_schema
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logger = require "logger-sharelatex"
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os = require "os"
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crypto = require "crypto"
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HOST = os.hostname()
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PID = process.pid
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RND = crypto.randomBytes(4).toString('hex')
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COUNT = 0
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module.exports = LockManager =
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LOCK_TEST_INTERVAL: 50 # 50ms between each test of the lock
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MAX_TEST_INTERVAL: 1000 # back off to 1s between each test of the lock
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MAX_LOCK_WAIT_TIME: 10000 # 10s maximum time to spend trying to get the lock
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LOCK_TTL: 30 # seconds. Time until lock auto expires in redis.
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# Use a signed lock value as described in
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# http://redis.io/topics/distlock#correct-implementation-with-a-single-instance
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# to prevent accidental unlocking by multiple processes
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randomLock : () ->
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time = Date.now()
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return "locked:host=#{HOST}:pid=#{PID}:random=#{RND}:time=#{time}:count=#{COUNT++}"
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unlockScript: 'if redis.call("get", KEYS[1]) == ARGV[1] then return redis.call("del", KEYS[1]) else return 0 end';
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tryLock : (doc_id, callback = (err, isFree)->)->
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lockValue = LockManager.randomLock()
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key = keys.blockingKey(doc_id:doc_id)
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logger.log {doc_id: doc_id, key: key}, "tryLock"
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rclient.set key, lockValue, "EX", @LOCK_TTL, "NX", (err, gotLock)->
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return callback(err) if err?
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if gotLock == "OK"
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metrics.inc "doc-not-blocking"
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logger.log {doc_id: doc_id, key: key, lockValue: lockValue}, "got lock"
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callback err, true, lockValue
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else
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metrics.inc "doc-blocking"
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logger.log {doc_id: doc_id, key: key}, "doc is locked"
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callback err, false
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getLock: (doc_id, callback = (error, lockValue) ->) ->
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startTime = Date.now()
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testInterval = LockManager.LOCK_TEST_INTERVAL
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do attempt = () ->
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if Date.now() - startTime > LockManager.MAX_LOCK_WAIT_TIME
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e = new Error("Timeout")
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e.doc_id = doc_id
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return callback(e)
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LockManager.tryLock doc_id, (error, gotLock, lockValue) ->
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return callback(error) if error?
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if gotLock
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callback(null, lockValue)
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else
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logger.log {doc_id: doc_id, delay: testInterval}, "will retry lock"
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setTimeout attempt, testInterval
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# back off when the lock is taken to avoid overloading
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testInterval = Math.min(testInterval * 2, LockManager.MAX_TEST_INTERVAL)
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checkLock: (doc_id, callback = (err, isFree)->)->
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key = keys.blockingKey(doc_id:doc_id)
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rclient.exists key, (err, exists) ->
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return callback(err) if err?
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exists = parseInt exists
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if exists == 1
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metrics.inc "doc-blocking"
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callback err, false
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else
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metrics.inc "doc-not-blocking"
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callback err, true
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releaseLock: (doc_id, lockValue, callback)->
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key = keys.blockingKey(doc_id:doc_id)
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rclient.eval LockManager.unlockScript, 1, key, lockValue, (err, result) ->
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if err?
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return callback(err)
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else if result? and result isnt 1 # successful unlock should release exactly one key
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logger.error {doc_id:doc_id, key:key, lockValue:lockValue, redis_err:err, redis_result:result}, "unlocking error"
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return callback(new Error("tried to release timed out lock"))
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else
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logger.log {doc_id:doc_id, key:key, lockValue:lockValue}, "released lock"
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callback(err,result)
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