Add a function to reuse a terminated VM.

exec/vm.go

@@ -340,6 +340,21 @@ func (vm *VirtualMachine) AddAndCheckGas(delta uint64) bool {
 	return true
 }
 
+// Reset makes de VM ready for a new call to Execute if the previous interruption
+// has been interrupted.
+func (vm *VirtualMachine) Reset() {
+	vm.CurrentFrame = -1
+	vm.Exited = false
+	vm.ExitError = nil
+	// The current depth of the callstack is a good indication of
+	// how deep it can go, clear all the current frames but leave
+	// it at its current allocation level.
+	for frame := range vm.CallStack {
+		vm.CallStack[frame] = Frame{}
+	}
+	vm.Delegate = nil
+}
+
 // Execute starts the virtual machines main instruction processing loop.
 // This function may return at any point and is guaranteed to return
 // at least once every 10000 instructions. Caller is responsible for

exec/vm_test.go

@@ -0,0 +1,45 @@
+package exec
+
+import "testing"
+
+var testCode = []byte{
+	0, 97, 115, 109, 1, 0, 0, 0, 1, 14, 3, 96, 2, 127, 127, 0, 96, 0, 0, 96, 2, 127, 127, 0, 2, 12, 1, 3, 109, 111, 100, 4, 116, 101, 115, 116, 0, 2, 3, 2, 1, 1, 5, 3, 1, 0, 17, 7, 17, 2, 6, 109, 101, 109, 111, 114, 121, 2, 0, 4, 109, 97, 105, 110, 0, 1, 10, 11, 1, 9, 0, 65, 0, 65, 247, 0, 16, 0, 11,
+}
+
+type MyResolver struct{}
+
+func (mr *MyResolver) ResolveFunc(module, field string) FunctionImport {
+	return func(vm *VirtualMachine) int64 {
+		panic("panic in order to trigger the VM's termination")
+		return 0
+	}
+}
+func (mr *MyResolver) ResolveGlobal(module, field string) int64 {
+	panic("not implemented")
+}
+
+func TestVMReset(t *testing.T) {
+	vm, err := NewVirtualMachine(testCode, VMConfig{}, &MyResolver{}, nil)
+	if err != nil {
+		t.Fatalf("Error creating VM: %v", err)
+	}
+	x := func() {
+		defer func() {
+			if err := recover(); err == nil {
+				t.Fatalf("an error should have been triggered")
+			}
+		}()
+		vm.Run(0, 0, 0)
+	}
+	x()
+	vm.Reset()
+	y := func() {
+		defer func() {
+			if err := recover(); err != nil && err != "panic in order to trigger the VM's termination" {
+				t.Fatalf("no panic or wrong type: %v", err)
+			}
+		}()
+		vm.Run(0, 1, 0)
+	}
+	y()
+}