Use Monitor to make sure we call RedisClient in a thread safe way.

README.md

@@ -176,14 +176,29 @@ lock_manager.get_remaining_ttl_for_resource(resource)
 
 ## Redis client configuration
 
-`Redlock::Client` expects URLs or Redis objects on initialization. Redis objects should be used for configuring the connection in more detail, i.e. setting username and password.
+`Redlock::Client` expects URLs, or configurations or Redis objects on initialization. Redis objects should be used for configuring the connection in more detail, i.e. setting username and password.
 
 ```ruby
 servers = [ 'redis://localhost:6379', RedisClient.new(:url => 'redis://someotherhost:6379') ]
 redlock = Redlock::Client.new(servers)
 ```
 
-Redlock works seamlessly with [redis sentinel](http://redis.io/topics/sentinel), which is supported in redis 3.2+.
+To utilize `Redlock::Client` with sentinels you can pass an instance of `RedisClient` or just a configuration hash as part of the servers array during initialization.
+
+```ruby
+config = {
+  name: "mymaster",
+  sentinels: [
+    { host: "127.0.0.1", port: 26380 },
+    { host: "127.0.0.1", port: 26381 },
+  ],
+  role: :master
+}
+client = RedisClient.sentinel(**config).new_client
+servers = [ config, client ]
+redlock = Redlock::Client.new(servers)
+```
+Redlock supports the same configuration hash as `RedisClient`.
 
 ## Redlock configuration
 

lib/redlock/client.rb

@@ -1,10 +1,11 @@
+require 'monitor'
 require 'redis-client'
 require 'securerandom'
 
 module Redlock
   include Scripts
 
-  class LockAcquisitionError < StandardError
+  class LockAcquisitionError < LockError
     attr_reader :errors
 
     def initialize(message, errors)
@@ -163,6 +164,8 @@ def with
       end
 
       def initialize(connection)
+        @monitor = Monitor.new
+
         if connection.respond_to?(:with)
           @redis = connection
         else
@@ -198,17 +201,21 @@ def initialize_client(options)
         end
       end
 
+      def synchronize
+        @monitor.synchronize { @redis.with { |connection| yield(connection) } }
+      end
+
       def lock(resource, val, ttl, allow_new_lock)
         recover_from_script_flush do
-          @redis.with { |conn|
+          synchronize { |conn|
             conn.call('EVALSHA', Scripts::LOCK_SCRIPT_SHA, 1, resource, val, ttl, allow_new_lock)
           }
         end
       end
 
       def unlock(resource, val)
         recover_from_script_flush do
-          @redis.with { |conn|
+          synchronize { |conn|
             conn.call('EVALSHA', Scripts::UNLOCK_SCRIPT_SHA, 1, resource, val)
           }
         end
@@ -218,7 +225,7 @@ def unlock(resource, val)
 
       def get_remaining_ttl(resource)
         recover_from_script_flush do
-          @redis.with { |conn|
+          synchronize { |conn|
             conn.call('EVALSHA', Scripts::PTTL_SCRIPT_SHA, 1, resource)
           }
         end
@@ -235,7 +242,7 @@ def load_scripts
           Scripts::PTTL_SCRIPT
         ]
 
-        @redis.with do |connnection|
+        synchronize do |connnection|
           scripts.each do |script|
             connnection.call('SCRIPT', 'LOAD', script)
           end