DataValidator: Hold concurrent requests

Since we maintain state (as a kluge for the time being to integrate
with the rest of the system), we need to be careful to protect against
concurrent requests that might mess with it before the original
request is complete.

* src/validate/DataValidator.js
  (validate, updateFailures): Hold concurrent requests.
  (_onceReady): Add method.

* test/validate/DataValidatorTest.js: Add tests.

src/validate/DataValidator.js

@@ -109,8 +109,8 @@ module.exports = Class( 'DataValidator',
     /**
      * Validate diff and update field monitor
      *
-     * If a validation is pending completion, all further `#validate`
+     * If an operation is pending completion, all further requests to this
-     * requests will be queued to prevent unexpected/inconsistent system
+     * object will be queued to prevent unexpected/inconsistent system
      * states and race conditions.
      *
      * The external validator `validatef` is a kluge while the system
@@ -126,16 +126,8 @@ module.exports = Class( 'DataValidator',
     {
         const _self = this;
 
-        // queue requests if we're already processing
+        return this._onceReady( () =>
-        if ( this._pending )
         {
-            this._pending.then(
-                () => this.validate( diff, classes, validatef )
-            );
-
-            return this._pending;
-        }
-
             let failures = {};
 
             if ( diff !== undefined )
@@ -156,14 +148,18 @@ module.exports = Class( 'DataValidator',
                 this._populateStore(
                     classes, this._stores.cstore, 'indexes'
                 )
-            .then( () => this.updateFailures( diff, failures ) )
+                .then( () => this._doUpdateFailures( diff, failures ) );
-            .then( () => this._pending = null );
+        } );
     },
 
 
     /**
      * Update failures from external validation
      *
+     * If an operation is pending completion, all further requests to this
+     * object will be queued to prevent unexpected/inconsistent system
+     * states and race conditions.
+     *
      * TODO: This is a transitional API---we should handle all validations,
      * not allow external systems to meddle in our affairs.
      *
@@ -173,6 +169,23 @@ module.exports = Class( 'DataValidator',
      * @return {Promise} promise to populate internal store
      */
     'public updateFailures'( diff, failures )
+    {
+        return this._onceReady( () =>
+        {
+            return this._doUpdateFailures( diff, failures );
+        } );
+    },
+
+
+    /**
+     * Update failures from external validation
+     *
+     * @param {Object} diff     bucket diff
+     * @param {Object} failures failures per field name and index
+     *
+     * @return {Promise} promise to populate internal store
+     */
+    'private _doUpdateFailures': function( diff, failures )
     {
         return this._populateStore( diff, this._stores.bstore ).then( () =>
             this._field_monitor.update(
@@ -198,10 +211,31 @@ module.exports = Class( 'DataValidator',
     'public clearFailures'( failures )
     {
         this._field_monitor.clearFailures( failures );
+
         return this;
     },
 
 
+    /**
+     * Wait until all requests are complete and then trigger callback
+     *
+     * @param {Function} callback callback to trigger when ready
+     *
+     * @return {Promise}
+     */
+    'private _onceReady': function( callback )
+    {
+        if ( this._pending )
+        {
+            this._pending.then( callback );
+            return this._pending;
+        }
+
+        return this._pending = callback()
+            .then( () => this._pending = null );
+    },
+
+
     /**
      * Populate store with data
      *

test/validate/DataValidatorTest.js

@@ -316,6 +316,42 @@ describe( 'DataValidator', () =>
                     );
                 } );
         } );
+
+
+        it( 'queues concurrent requests', () =>
+        {
+            const { sut, vmonitor, getStore } = createStubs( {
+                vmonitor: sinon.createStubInstance( ValidStateMonitor ),
+            } );
+            const { bstore } = getStore();
+
+            const faila = {};
+            const failb = {};
+
+            let running_first = true;
+
+            vmonitor.update = ( _, fail ) =>
+            {
+                if ( fail === failb )
+                {
+                    if ( running_first === true )
+                    {
+                        return Promise.reject( Error(
+                            "Request not queued"
+                        ) );
+                    }
+                }
+
+                return Promise.resolve( true );
+            };
+
+            return Promise.all( [
+                sut.updateFailures( {}, faila )
+                    .then( () => running_first = false ),
+
+                sut.updateFailures( {}, failb ),
+            ] );
+        } );
     } );