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promise_util.h
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promise_util.h
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// Copyright (c) 2018 GitHub, Inc.
// Use of this source code is governed by the MIT license that can be
// found in the LICENSE file.
#ifndef SHELL_COMMON_PROMISE_UTIL_H_
#define SHELL_COMMON_PROMISE_UTIL_H_
#include <string>
#include <tuple>
#include <type_traits>
#include <utility>
#include "base/strings/string_piece.h"
#include "base/task/post_task.h"
#include "content/public/browser/browser_task_traits.h"
#include "content/public/browser/browser_thread.h"
#include "native_mate/converter.h"
#include "native_mate/microtasks_scope.h"
#include "shell/common/gin_converters/std_converter.h"
namespace electron {
namespace util {
// A wrapper around the v8::Promise.
//
// This is a move-only type that should always be `std::move`d when passed to
// callbacks, and it should be destroyed on the same thread of creation.
template <typename RT>
class Promise {
public:
// Create a new promise.
explicit Promise(v8::Isolate* isolate)
: Promise(isolate,
v8::Promise::Resolver::New(isolate->GetCurrentContext())
.ToLocalChecked()) {}
// Wrap an existing v8 promise.
Promise(v8::Isolate* isolate, v8::Local<v8::Promise::Resolver> handle)
: isolate_(isolate),
context_(isolate, isolate->GetCurrentContext()),
resolver_(isolate, handle) {}
~Promise() = default;
// Support moving.
Promise(Promise&&) = default;
Promise& operator=(Promise&&) = default;
v8::Isolate* isolate() const { return isolate_; }
v8::Local<v8::Context> GetContext() {
return v8::Local<v8::Context>::New(isolate_, context_);
}
// helpers for promise resolution and rejection
static void ResolvePromise(Promise<RT> promise, RT result) {
if (!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI)) {
base::PostTask(
FROM_HERE, {content::BrowserThread::UI},
base::BindOnce([](Promise<RT> promise,
RT result) { promise.ResolveWithGin(result); },
std::move(promise), std::move(result)));
} else {
promise.ResolveWithGin(result);
}
}
static void ResolveEmptyPromise(Promise<RT> promise) {
if (!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI)) {
base::PostTask(
FROM_HERE, {content::BrowserThread::UI},
base::BindOnce([](Promise<RT> promise) { promise.Resolve(); },
std::move(promise)));
} else {
promise.Resolve();
}
}
static void RejectPromise(Promise<RT> promise, base::StringPiece errmsg) {
if (!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI)) {
base::PostTask(FROM_HERE, {content::BrowserThread::UI},
base::BindOnce(
[](Promise<RT> promise, base::StringPiece err) {
promise.RejectWithErrorMessage(err);
},
std::move(promise), std::move(errmsg)));
} else {
promise.RejectWithErrorMessage(errmsg);
}
}
// Returns an already-resolved promise.
static v8::Local<v8::Promise> ResolvedPromise(v8::Isolate* isolate,
RT result) {
Promise<RT> resolved(isolate);
resolved.Resolve(result);
return resolved.GetHandle();
}
static v8::Local<v8::Promise> ResolvedPromise(v8::Isolate* isolate) {
Promise<void*> resolved(isolate);
resolved.Resolve();
return resolved.GetHandle();
}
v8::Local<v8::Promise> GetHandle() const { return GetInner()->GetPromise(); }
v8::Maybe<bool> Resolve() {
static_assert(std::is_same<void*, RT>(),
"Can only resolve void* promises with no value");
v8::HandleScope handle_scope(isolate());
mate::MicrotasksScope microtasks_scope(isolate());
v8::Context::Scope context_scope(
v8::Local<v8::Context>::New(isolate(), GetContext()));
return GetInner()->Resolve(GetContext(), v8::Undefined(isolate()));
}
v8::Maybe<bool> Reject() {
v8::HandleScope handle_scope(isolate());
mate::MicrotasksScope microtasks_scope(isolate());
v8::Context::Scope context_scope(
v8::Local<v8::Context>::New(isolate(), GetContext()));
return GetInner()->Reject(GetContext(), v8::Undefined(isolate()));
}
v8::Maybe<bool> Reject(v8::Local<v8::Value> exception) {
v8::HandleScope handle_scope(isolate());
mate::MicrotasksScope microtasks_scope(isolate());
v8::Context::Scope context_scope(
v8::Local<v8::Context>::New(isolate(), GetContext()));
return GetInner()->Reject(GetContext(), exception);
}
template <typename... ResolveType>
v8::MaybeLocal<v8::Promise> Then(
base::OnceCallback<void(ResolveType...)> cb) {
static_assert(sizeof...(ResolveType) <= 1,
"A promise's 'Then' callback should only receive at most one "
"parameter");
static_assert(
std::is_same<RT, std::tuple_element_t<0, std::tuple<ResolveType...>>>(),
"A promises's 'Then' callback must handle the same type as the "
"promises resolve type");
v8::HandleScope handle_scope(isolate());
v8::Context::Scope context_scope(
v8::Local<v8::Context>::New(isolate(), GetContext()));
v8::Local<v8::Value> value = gin::ConvertToV8(isolate(), std::move(cb));
v8::Local<v8::Function> handler = v8::Local<v8::Function>::Cast(value);
return GetHandle()->Then(GetContext(), handler);
}
// Promise resolution is a microtask
// We use the MicrotasksRunner to trigger the running of pending microtasks
v8::Maybe<bool> Resolve(const RT& value) {
static_assert(!std::is_same<void*, RT>(),
"void* promises can not be resolved with a value");
v8::HandleScope handle_scope(isolate());
mate::MicrotasksScope microtasks_scope(isolate());
v8::Context::Scope context_scope(
v8::Local<v8::Context>::New(isolate(), GetContext()));
return GetInner()->Resolve(GetContext(),
mate::ConvertToV8(isolate(), value));
}
v8::Maybe<bool> ResolveWithGin(const RT& value) {
static_assert(!std::is_same<void*, RT>(),
"void* promises can not be resolved with a value");
v8::HandleScope handle_scope(isolate());
mate::MicrotasksScope microtasks_scope(isolate());
v8::Context::Scope context_scope(
v8::Local<v8::Context>::New(isolate(), GetContext()));
return GetInner()->Resolve(GetContext(),
gin::ConvertToV8(isolate(), value));
}
v8::Maybe<bool> RejectWithErrorMessage(base::StringPiece string) {
v8::HandleScope handle_scope(isolate());
mate::MicrotasksScope microtasks_scope(isolate());
v8::Context::Scope context_scope(
v8::Local<v8::Context>::New(isolate(), GetContext()));
v8::Local<v8::Value> error =
v8::Exception::Error(gin::StringToV8(isolate(), string));
return GetInner()->Reject(GetContext(), (error));
}
private:
v8::Local<v8::Promise::Resolver> GetInner() const {
return resolver_.Get(isolate());
}
v8::Isolate* isolate_;
v8::Global<v8::Context> context_;
v8::Global<v8::Promise::Resolver> resolver_;
DISALLOW_COPY_AND_ASSIGN(Promise);
};
} // namespace util
} // namespace electron
namespace mate {
template <typename T>
struct Converter<electron::util::Promise<T>> {
static v8::Local<v8::Value> ToV8(v8::Isolate* isolate,
const electron::util::Promise<T>& val);
// TODO(MarshallOfSound): Implement FromV8 to allow promise chaining
// in native land
// static bool FromV8(v8::Isolate* isolate,
// v8::Local<v8::Value> val,
// Promise* out);
};
} // namespace mate
#endif // SHELL_COMMON_PROMISE_UTIL_H_