I've been trying to figure out how to make asynchronous calls in V8, without luck. The example javascript code I'm trying to have run is:
function test ()
{
logMessage ('asynchronous call made!');
}
saveFunc(test);
The saveFunc function is supposed to save the test function for use when the C++ code calls it later after the script is ran. Everytime I try this it crashes when I try to execute the function that was saved. What am I doing wrong?
I've copied my entire example code below. Thanks in advance.
Example Code:
// Copyright 2015 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <iostream>
#include <string>
#include "libplatform/libplatform.h"
#include "v8.h"
using namespace v8;
Local<Context> context;
v8::Local<v8::Function> savedFunc;
class ArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
public:
virtual void* Allocate(size_t length) {
void* data = AllocateUninitialized(length);
return data == NULL ? data : memset(data, 0, length);
}
virtual void* AllocateUninitialized(size_t length) { return malloc(length); }
virtual void Free(void* data, size_t) { free(data); }
};
std::string parseV8Value(v8::Local<v8::Value> str)
{
if (str.IsEmpty() == true)
return ("");
v8::String::Utf8Value newStr(str);
return (*newStr);
}
void logMessage(const v8::FunctionCallbackInfo<v8::Value> &args)
{
std::string applicationSource = parseV8Value(args[0]);
std::cout << applicationSource << "\n";
}
void getInput(const v8::FunctionCallbackInfo<v8::Value> &args)
{
v8::Local<v8::Function> func = v8::Local<v8::Function>::Cast (args[0]);
std::string input = "";
std::cin >> input;
v8::Local<v8::Value> *args2 = new v8::Local<v8::Value>[1];
args2[0] = v8::String::NewFromUtf8 (args.GetIsolate (), input.c_str ());
func->Call (context->Global (), 1, args2);
delete []args2;
args2 = NULL;
}
void saveFunc(const v8::FunctionCallbackInfo<v8::Value> &args)
{
savedFunc = v8::Local<v8::Function>::Cast(args[0]);
}
int main(int argc, char* argv[]) {
// Initialize V8.
V8::InitializeICU();
V8::InitializeExternalStartupData(argv[0]);
Platform* platform = platform::CreateDefaultPlatform();
V8::InitializePlatform(platform);
V8::Initialize();
// Create a new Isolate and make it the current one.
ArrayBufferAllocator allocator;
Isolate::CreateParams create_params;
create_params.array_buffer_allocator = &allocator;
Isolate* isolate = Isolate::New(create_params);
{
Isolate::Scope isolate_scope(isolate);
// Create a stack-allocated handle scope.
HandleScope handle_scope(isolate);
// Create a new context.
v8::Local<v8::ObjectTemplate> global = v8::ObjectTemplate::New(isolate);
global->Set(v8::String::NewFromUtf8(isolate, "logMessage"),
v8::FunctionTemplate::New(isolate, logMessage));
global->Set(v8::String::NewFromUtf8(isolate, "getInput"),
v8::FunctionTemplate::New(isolate, getInput));
global->Set(v8::String::NewFromUtf8(isolate, "saveFunc"),
v8::FunctionTemplate::New(isolate, saveFunc));
context = Context::New(isolate, NULL, global);
// Enter the context for compiling and running the hello world script.
Context::Scope context_scope(context);
// Create a string containing the JavaScript source code.
Local<String> source =
String::NewFromUtf8(isolate,
"function test (){ logMessage ('asynchronous call made!'); }saveFunc(test);",,
NewStringType::kNormal).ToLocalChecked();
// Compile the source code.
Local<Script> script = Script::Compile(context, source).ToLocalChecked();
// Run the script to get the result.
Local<Value> result = script->Run(context).ToLocalChecked();
v8::Local<v8::Value> *args = new v8::Local<v8::Value>[0];
savedFunc->Call(context->Global(), 0, args);
delete []args;
args = NULL;
}
// Dispose the isolate and tear down V8.
isolate->Dispose();
V8::Dispose();
V8::ShutdownPlatform();
delete platform;
return 0;
}
Ok, so you have to use a Persistent handle when saving the function in saveFunc. Also, you have to make sure that when you're accessing context->Global, that you're still within the HandleScope. Here's the corrected code:
// Copyright 2015 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <iostream>
#include <string>
#include "libplatform/libplatform.h"
#include "v8.h"
using namespace v8;
Isolate* isolate = NULL;
Local<Context> context;
v8::Persistent<v8::Function> *savedFunc = NULL;
class ArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
public:
virtual void* Allocate(size_t length) {
void* data = AllocateUninitialized(length);
return data == NULL ? data : memset(data, 0, length);
}
virtual void* AllocateUninitialized(size_t length) { return malloc(length); }
virtual void Free(void* data, size_t) { free(data); }
};
std::string parseV8Value(v8::Local<v8::Value> str)
{
if (str.IsEmpty() == true)
return ("");
v8::String::Utf8Value newStr(str);
return (*newStr);
}
void logMessage(const v8::FunctionCallbackInfo<v8::Value> &args)
{
std::string applicationSource = parseV8Value(args[0]);
std::cout << applicationSource << "\n";
}
void getInput(const v8::FunctionCallbackInfo<v8::Value> &args)
{
v8::Local<v8::Function> func = v8::Local<v8::Function>::Cast (args[0]);
std::string input = "";
std::cin >> input;
v8::Local<v8::Value> *args2 = new v8::Local<v8::Value>[1];
args2[0] = v8::String::NewFromUtf8 (args.GetIsolate (), input.c_str ());
func->Call (context->Global (), 1, args2);
delete []args2;
args2 = NULL;
}
void saveFunc(const v8::FunctionCallbackInfo<v8::Value> &args)
{
v8::Local<v8::Function> func = v8::Local<v8::Function>::Cast(args[0]);
savedFunc = new v8::Persistent<v8::Function>();
savedFunc->Reset(isolate, func);
}
int main(int argc, char* argv[]) {
// Initialize V8.
V8::InitializeICU();
V8::InitializeExternalStartupData(argv[0]);
Platform* platform = platform::CreateDefaultPlatform();
V8::InitializePlatform(platform);
V8::Initialize();
// Create a new Isolate and make it the current one.
ArrayBufferAllocator allocator;
Isolate::CreateParams create_params;
create_params.array_buffer_allocator = &allocator;
isolate = Isolate::New(create_params);
{
Isolate::Scope isolate_scope(isolate);
// Create a stack-allocated handle scope.
HandleScope handle_scope(isolate);
// Create a new context.
v8::Local<v8::ObjectTemplate> global = v8::ObjectTemplate::New(isolate);
global->Set(v8::String::NewFromUtf8(isolate, "logMessage"),
v8::FunctionTemplate::New(isolate, logMessage));
global->Set(v8::String::NewFromUtf8(isolate, "getInput"),
v8::FunctionTemplate::New(isolate, getInput));
global->Set(v8::String::NewFromUtf8(isolate, "saveFunc"),
v8::FunctionTemplate::New(isolate, saveFunc));
context = Context::New(isolate, NULL, global);
// Enter the context for compiling and running the hello world script.
Context::Scope context_scope(context);
// The "asynchronous" javascript call to make
Local<String> source =
String::NewFromUtf8(isolate,
"function test (){ logMessage ('asynchronous call made!'); }saveFunc(test);",
NewStringType::kNormal).ToLocalChecked();
// Compile the source code.
Local<Script> script = Script::Compile(context, source).ToLocalChecked();
// Run the script to get the result.
Local<Value> result = script->Run(context).ToLocalChecked();
v8::Local<v8::Value> *args = new v8::Local<v8::Value>[0];
v8::Local<v8::Value> recv = context->Global();
v8::Local<v8::Function> func = savedFunc->Get(isolate);
func->Call (recv, 0, args);
delete savedFunc;
savedFunc = NULL;
delete []args;
args = NULL;
}
// Dispose the isolate and tear down V8.
isolate->Dispose();
V8::Dispose();
V8::ShutdownPlatform();
delete platform;
return 0;
}