Remove VM-locking yield mode per discussion

src/blocks/scratch3_operators.js

@@ -78,11 +78,10 @@ Scratch3OperatorsBlocks.prototype.not = function (args) {
     return Boolean(!args.OPERAND);
 };
 
-Scratch3OperatorsBlocks.prototype.random = function (args, util) {
+Scratch3OperatorsBlocks.prototype.random = function (args) {
     // As a demo, this implementation of random returns after 1 second of yield.
     // @todo Match Scratch 2.0 implementation with int-truncation.
     // See: http://bit.ly/1Qc0GzC
-    util.yieldAndBlock();
     var examplePromise = new Promise(function(resolve) {
         setTimeout(function() {
             var res = (Math.random() * (args.TO - args.FROM)) + args.FROM;

src/engine/execute.js

@@ -74,7 +74,6 @@ var execute = function (sequencer, thread) {
     var primitiveReportedValue = null;
     primitiveReportedValue = blockFunction(argValues, {
         yield: thread.yield.bind(thread),
-        yieldAndBlock: thread.yieldAndBlock.bind(thread),
         done: function() {
             sequencer.proceedThread(thread);
         },

src/engine/sequencer.js

@@ -32,13 +32,6 @@ Sequencer.WORK_TIME = 10;
 Sequencer.prototype.stepThreads = function (threads) {
     // Start counting toward WORK_TIME
     this.timer.start();
-    // Check for a blocking thread.
-    var blockingThread = this.getBlockingThread_(threads);
-    if (blockingThread) {
-        // Attempt to resolve any timeouts, but otherwise stop stepping.
-        blockingThread.resolveTimeouts();
-        return [];
-    }
     // List of threads which have been killed by this step.
     var inactiveThreads = [];
     // If all of the threads are yielding, we should yield.
@@ -70,10 +63,6 @@ Sequencer.prototype.stepThreads = function (threads) {
                 activeThread.status = Thread.STATUS_RUNNING;
                 // @todo Deal with the return value
             }
-            // Has the thread gone into "blocking" mode? If so, stop stepping.
-            if (activeThread.status === Thread.STATUS_YIELD_BLOCK) {
-                return inactiveThreads;
-            }
             if (activeThread.stack.length === 0 &&
                 activeThread.status === Thread.STATUS_DONE) {
                 // Finished with this thread - tell runtime to clean it up.
@@ -89,20 +78,6 @@ Sequencer.prototype.stepThreads = function (threads) {
     return inactiveThreads;
 };
 
-/**
- * Return the thread blocking all other threads, if one exists.
- * @param {Array.<Thread>} threads List of which threads to check.
- * @return {?Thread} The blocking thread if one exists.
- */
-Sequencer.prototype.getBlockingThread_ = function (threads) {
-    for (var i = 0; i < threads.length; i++) {
-        if (threads[i].status === Thread.STATUS_YIELD_BLOCK) {
-            return threads[i];
-        }
-    }
-    return null;
-};
-
 /**
  * Step the requested thread
  * @param {!Thread} thread Thread object to step

src/engine/thread.js

@@ -52,21 +52,13 @@ Thread.STATUS_RUNNING = 0;
  */
 Thread.STATUS_YIELD = 1;
 
-/**
- * Thread status for a yielded thread that should block all other threads.
- * This is desirable when an asynchronous capability should appear to take
- * a synchronous amount of time (e.g., color touching color).
- * @const
- */
-Thread.STATUS_YIELD_BLOCK = 2;
-
 /**
  * Thread status for a finished/done thread.
  * Thread is moved to this state when the interpreter
  * can proceed with execution.
  * @const
  */
-Thread.STATUS_DONE = 3;
+Thread.STATUS_DONE = 2;
 
 /**
  * Push stack and update stack frames appropriately.
@@ -139,13 +131,6 @@ Thread.prototype.yield = function () {
     this.status = Thread.STATUS_YIELD;
 };
 
-/**
- * Yields the thread and blocks other threads until unyielded.
- */
-Thread.prototype.yieldAndBlock = function () {
-    this.status = Thread.STATUS_YIELD_BLOCK;
-};
-
 /**
  * Add an execution-synced timeouts for this thread.
  * See also: util/yieldtimers.js:timeout