feat: added "readLock" option to aquireLock function

tristanls · Dec 6, 2018 · 5363fe3 · 5363fe3
1 parent 00f0e10
commit 5363fe3
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Showing 2 changed files with 25 additions and 3 deletions.
diff --git a/README.md b/README.md
@@ -182,9 +182,11 @@ Creates a "fail closed" client that acquires "fail closed" locks. If process cra
 
 Creates a "fail open" client that acquires "fail open" locks. If process crashes and lock is not released, lock will eventually expire after `leaseDurationMs` from last heartbeat sent (if any). This means that if process acquires a lock, goes to sleep for more than `leaseDurationMs`, and then wakes up assuming it still has a lock, then it can perform an operation ignoring other processes that may assume they have a lock on the operation.
 
-### client.acquireLock(id, callback)
+### client.acquireLock(id, [opt], callback)
 
   * `id`: _String\|Buffer\|Number_ Unique identifier for the lock. The type must correspond to lock table's partition key type.
+  * `opt`: _Object_ Options, optionally containing
+    * readLock: _Boolean_ Indicate if this is a read lock.
   * `callback`: _Function_ `(error, lock) => {}`
     * `error`: _Error_ Error, if any.
     * `lock`: _DynamoDBLockClient.Lock_ Successfully acquired lock object. Lock object is an instance of `EventEmitter`. If the `lock` is acquired via a fail open `client` configured to heartbeat, then the returned `lock` may emit an `error` event if a `heartbeat` operation fails.

diff --git a/index.js b/index.js
@@ -40,8 +40,13 @@ FailClosed.schema =
     config: require("./schema/failClosedConfig.js")
 };
 
-FailClosed.prototype.acquireLock = function(id, callback)
+FailClosed.prototype.acquireLock = function(id, opts, callback)
 {
+    if (callback === undefined)
+    {
+        callback = opts;
+        opts = {};
+    }
     const self = this;
     const workflow = new events.EventEmitter();
     setImmediate(() => workflow.emit("start",
@@ -69,6 +74,11 @@ FailClosed.prototype.acquireLock = function(id, callback)
                     "#partitionKey": self._partitionKey
                 }
             };
+            if (opts.readLock === true)
+            {
+                params.Item.readLock = 'readLock';
+                params.ConditionExpression += ' AND attribute_not_exists(readLock)';
+            }
             params.Item[self._partitionKey] = dataBag.id;
             self._dynamodb.put(params, (error, data) =>
                 {
@@ -147,8 +157,13 @@ FailOpen.schema =
     config: require("./schema/failOpenConfig.js")
 };
 
-FailOpen.prototype.acquireLock = function(id, callback)
+FailOpen.prototype.acquireLock = function(id, opts, callback)
 {
+    if (callback === undefined)
+    {
+        callback = opts;
+        opts = {};
+    }
     const self = this;
     const workflow = new events.EventEmitter();
     setImmediate(() => workflow.emit("start",
@@ -220,6 +235,11 @@ FailOpen.prototype.acquireLock = function(id, callback)
                     "#partitionKey": self._partitionKey
                 }
             };
+            if (opts.readLock === true)
+            {
+                params.Item.readLock = 'readLock';
+                params.ConditionExpression += ' AND attribute_not_exists(readLock)';
+            }
             if (self._trustLocalTime)
             {
                 params.Item.lockAcquiredTimeUnixMs = (new Date()).getTime();