Add simple promise API to VirtualMachine

Author: adazem009

include/scratchcpp/virtualmachine.h

@@ -133,6 +133,8 @@ class LIBSCRATCHCPP_EXPORT VirtualMachine
         void moveToLastCheckpoint();
 
         void stop(bool savePos = true, bool breakFrame = false, bool goBack = false);
+        void promise();
+        void resolvePromise();
 
         bool atEnd() const;
 

src/engine/virtualmachine.cpp

@@ -166,6 +166,9 @@ void VirtualMachine::run()
 {
     impl->running = true;
 
+    if (impl->promisePending)
+        return;
+
     unsigned int *ret = impl->run(impl->pos);
     assert(ret);
 
@@ -187,6 +190,7 @@ void VirtualMachine::reset()
 {
     impl->pos = impl->bytecode;
     impl->atEnd = false;
+    impl->promisePending = false;
 
     if (!impl->running) // Registers will be freed when the script stops running
         impl->regCount = 0;
@@ -216,6 +220,22 @@ void VirtualMachine::stop(bool savePos, bool breakFrame, bool goBack)
     impl->goBack = goBack;
 }
 
+/*!
+ * Use this to pause the execution of the script.
+ * The execution will continue after calling resolvePromise()
+ */
+void VirtualMachine::promise()
+{
+    impl->promisePending = true;
+    stop();
+}
+
+/*! Resolves the promise so that the VM can continue with the execution. */
+void VirtualMachine::resolvePromise()
+{
+    impl->promisePending = false;
+}
+
 /*! Returns true if the VM has reached the vm::OP_HALT instruction. */
 bool VirtualMachine::atEnd() const
 {

src/engine/virtualmachine_p.h

@@ -56,6 +56,7 @@ struct VirtualMachinePrivate
         bool savePos = true;
         bool goBack = false;
         bool updatePos = false;
+        bool promisePending = false;
 
         unsigned int **procedures = nullptr;
         BlockFunc *functions = nullptr;

test/virtual_machine/virtual_machine_test.cpp

@@ -1639,6 +1639,35 @@ TEST(VirtualMachineTest, ResetAndKill)
     ASSERT_TRUE(vm.atEnd());
 }
 
+unsigned int promiseTest(VirtualMachine *vm)
+{
+    vm->promise();
+    return 1;
+}
+
+TEST(VirtualMachineTest, Promise)
+{
+    static unsigned int bytecode[] = { OP_START, OP_NULL, OP_EXEC, 0, vm::OP_NULL, vm::OP_NULL, vm::OP_NULL, OP_HALT };
+    static BlockFunc functions[] = { &promiseTest };
+
+    VirtualMachine vm;
+    vm.setBytecode(bytecode);
+    vm.setFunctions(functions);
+
+    vm.run();
+    ASSERT_FALSE(vm.atEnd());
+    ASSERT_EQ(vm.registerCount(), 0);
+
+    vm.run();
+    ASSERT_FALSE(vm.atEnd());
+    ASSERT_EQ(vm.registerCount(), 0);
+
+    vm.resolvePromise();
+    vm.run();
+    ASSERT_TRUE(vm.atEnd());
+    ASSERT_EQ(vm.registerCount(), 3);
+}
+
 TEST(VirtualMachineTest, NoCrashWhenRepeatingZeroTimes)
 {
     // Regtest for #362