Make the notebook execution buffer move repeatedly executed cells to the end of the queue.

This is consistent with how execution works, since the cell is only finally executed with the final text of the cell.

This may still give surprising results, for example, if cell 1 defines a variable and cell 2 increments and prints the variable.
If the execution order is cell 1, cell 2, cell 1, then before this commit cell 2 would print fine, whereas now cell 2 will throw an error.

Author: jasongrout

notebook/static/notebook/js/notebook.js

@@ -2234,7 +2234,17 @@ define(function (require) {
     Notebook.prototype.execute = function (cell) {
         var executed = cell.execute();
         if (!executed) {
-            this.pending_execution.push(cell)
+            var pending = this.pending_execution;
+            var index = pending.indexOf(cell);
+            if (index >= 0 ) {
+                // if the cell is already pending, move it to the end
+                for (var i = index; i < pending.length - 1; i++) {
+                    pending[i] = pending[i+1];
+                }
+                pending[pending.length - 1] = cell;
+            } else {
+                pending.push(cell);
+            }
         }
     }
 

notebook/tests/notebook/buffering.js

@@ -2,10 +2,17 @@
 // Test buffering for execution requests.
 //
 casper.notebook_test(function () {
-    this.evaluate(function () {
+    this.then(function() {
+      // make sure there are at least three cells for the tests below.
+      this.append_cell();
+      this.append_cell();
+      this.append_cell();
+    })
+
+    this.thenEvaluate(function () {
+        IPython.notebook.kernel.stop_channels();
         var cell = IPython.notebook.get_cell(0);
         cell.set_text('a=10; print(a)');
-        IPython.notebook.kernel.stop_channels();
         IPython.notebook.execute_cells([0]);
         IPython.notebook.kernel.reconnect(1);
     });
@@ -16,7 +23,7 @@ casper.notebook_test(function () {
         var result = this.get_output_cell(0);
         this.test.assertEquals(result.text, '10\n', 'kernels buffer execution requests if connection is down');
     });
-    
+
     this.thenEvaluate(function () {
         var cell = IPython.notebook.get_cell(0);
         cell.set_text('a=11; print(a)');
@@ -33,4 +40,71 @@ casper.notebook_test(function () {
         this.test.assertEquals(result.text, '11\n', 'notebooks buffer cell execution requests if kernel is not set');
     });
 
+    // Repeated execution behavior differs in the two queues
+
+    this.thenEvaluate(function () {
+
+        var cell = IPython.notebook.get_cell(0);
+        var cellplus = IPython.notebook.get_cell(1);
+        var cellprint = IPython.notebook.get_cell(2);
+        cell.set_text('k=1');
+        cellplus.set_text('k+=1');
+        cellprint.set_text('k*=2')
+
+        IPython.notebook.kernel.stop_channels();
+
+        // Repeated execution of cell queued up in the kernel executes
+        // each execution request.
+        IPython.notebook.execute_cells([0]);
+        IPython.notebook.execute_cells([2]);
+        IPython.notebook.execute_cells([1]);
+        IPython.notebook.execute_cells([1]);
+        IPython.notebook.execute_cells([1]);
+        cellprint.set_text('print(k)')
+        IPython.notebook.execute_cells([2]);        
+
+        IPython.notebook.kernel.reconnect(1);
+    });
+
+    this.wait_for_output(2);
+    
+    this.then(function () {
+        var result = this.get_output_cell(2);
+        this.test.assertEquals(result.text, '5\n', 'kernel message buffer sends each message queued');
+    });
+
+    this.thenEvaluate(function () {
+
+        var cell = IPython.notebook.get_cell(0);
+        var cellplus = IPython.notebook.get_cell(1);
+        var cellprint = IPython.notebook.get_cell(2);
+        cell.set_text('n=1');
+        cellplus.set_text('n+=1');
+        cellprint.set_text('n*=2')
+
+        cell.kernel = null;
+        cellplus.kernel = null;
+        cellprint.kernel = null;
+        IPython.notebook.kernel = null;
+
+        // Repeated execution of cell queued up in the notebook moves the cell
+        // to the end of the queue, only executing it once.
+        IPython.notebook.execute_cells([0]);
+        IPython.notebook.execute_cells([2]);
+        IPython.notebook.execute_cells([1]);
+        IPython.notebook.execute_cells([1]);
+        IPython.notebook.execute_cells([1]);
+        cellprint.set_text('print(n)')
+        IPython.notebook.execute_cells([2]);        
+
+        IPython.notebook._session_started();
+    });
+
+    this.wait_for_output(2);
+    
+    this.then(function () {
+        var result = this.get_output_cell(2);
+        this.test.assertEquals(result.text, '2\n', 'notebook execution buffer moves repeatedly executed cell to end of queue');
+    });
+
 });