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// Copyright 2013 The Flutter 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 "flutter/runtime/dart_vm_lifecycle.h"
#include <mutex>
namespace flutter {
// We need to explicitly put the constructor and destructor of the DartVM in the
// critical section. All accesses (not just const members) to the global VM
// object weak pointer are behind this mutex.
static std::mutex gVMMutex;
static std::weak_ptr<DartVM> gVM;
static std::shared_ptr<DartVM>* gVMLeak;
// We are going to be modifying more than just the control blocks of the
// following weak pointers (in the |Create| case where an old VM could not be
// reused). Ideally, we would use |std::atomic<std::weak_ptr<T>>| specialization
// but that is only available since C++20. We don't expect contention on these
// locks so we just use one mutex for all.
static std::mutex gVMDependentsMutex;
static std::weak_ptr<const DartVMData> gVMData;
static std::weak_ptr<ServiceProtocol> gVMServiceProtocol;
static std::weak_ptr<IsolateNameServer> gVMIsolateNameServer;
DartVMRef::DartVMRef(std::shared_ptr<DartVM> vm) : vm_(vm) {}
DartVMRef::DartVMRef(DartVMRef&& other) = default;
DartVMRef::~DartVMRef() {
if (!vm_) {
// If there is no valid VM (possible via a move), there is no way that the
// decrement on the shared pointer can cause a collection. Avoid acquiring
// the lifecycle lock in this case. This is just working around a
// pessimization and not required for correctness.
std::scoped_lock lifecycle_lock(gVMMutex);
DartVMRef DartVMRef::Create(Settings settings,
fml::RefPtr<const DartSnapshot> vm_snapshot,
fml::RefPtr<const DartSnapshot> isolate_snapshot) {
std::scoped_lock lifecycle_lock(gVMMutex);
if (!settings.leak_vm) {
<< "Launch settings indicated that the VM should shut down in the "
"process when done but a previous launch asked the VM to leak in "
"the same process. For proper VM shutdown, all VM launches must "
"indicate that they should shut down when done.";
// If there is already a running VM in the process, grab a strong reference to
// it.
if (auto vm = gVM.lock()) {
FML_DLOG(WARNING) << "Attempted to create a VM in a process where one was "
"already running. Ignoring arguments for current VM "
"create call and reusing the old VM.";
// There was already a running VM in the process,
return DartVMRef{std::move(vm)};
std::scoped_lock dependents_lock(gVMDependentsMutex);
// If there is no VM in the process. Initialize one, hold the weak reference
// and pass a strong reference to the caller.
auto isolate_name_server = std::make_shared<IsolateNameServer>();
auto vm = DartVM::Create(std::move(settings), //
std::move(vm_snapshot), //
std::move(isolate_snapshot), //
isolate_name_server //
if (!vm) {
FML_LOG(ERROR) << "Could not create Dart VM instance.";
return {nullptr};
gVMData = vm->GetVMData();
gVMServiceProtocol = vm->GetServiceProtocol();
gVMIsolateNameServer = isolate_name_server;
gVM = vm;
if (settings.leak_vm) {
gVMLeak = new std::shared_ptr<DartVM>(vm);
return DartVMRef{std::move(vm)};
bool DartVMRef::IsInstanceRunning() {
std::scoped_lock lock(gVMMutex);
return !gVM.expired();
std::shared_ptr<const DartVMData> DartVMRef::GetVMData() {
std::scoped_lock lock(gVMDependentsMutex);
return gVMData.lock();
std::shared_ptr<ServiceProtocol> DartVMRef::GetServiceProtocol() {
std::scoped_lock lock(gVMDependentsMutex);
return gVMServiceProtocol.lock();
std::shared_ptr<IsolateNameServer> DartVMRef::GetIsolateNameServer() {
std::scoped_lock lock(gVMDependentsMutex);
return gVMIsolateNameServer.lock();
DartVM* DartVMRef::GetRunningVM() {
std::scoped_lock lock(gVMMutex);
auto vm = gVM.lock().get();
FML_CHECK(vm) << "Caller assumed VM would be running when it wasn't";
return vm;
} // namespace flutter