Replace custom synchronization with absl::Notification

PiperOrigin-RevId: 248334969
Change-Id: I7614a3792babd399912c5d5a167ab5e0a0574d20

sandboxed_api/sandbox2/monitor.cc

@@ -112,7 +112,6 @@ Monitor::Monitor(Executor* executor, Policy* policy, Notify* notify)
       policy_(policy),
       comms_(executor_->ipc()->comms()),
       ipc_(executor_->ipc()),
-      setup_counter_(1),
       wait_for_execve_(executor->enable_sandboxing_pre_execve_) {
   std::string path =
       absl::GetFlag(FLAGS_sandbox2_danger_danger_permit_all_and_log);
@@ -141,10 +140,9 @@ void LogContainer(const std::vector<std::string>& container) {
 }  // namespace
 
 void Monitor::Run() {
-  using DecrementCounter = decltype(setup_counter_);
+  std::unique_ptr<absl::Notification, void (*)(absl::Notification*)>
-  std::unique_ptr<DecrementCounter, void (*)(DecrementCounter*)>
+      setup_notify{&setup_notification_, [](absl::Notification* notification) {
-      decrement_count{&setup_counter_, [](DecrementCounter* counter) {
+                     notification->Notify();
-                        counter->DecrementCount();
                    }};
 
   struct MonitorCleanup {
@@ -152,8 +150,7 @@ void Monitor::Run() {
       getrusage(RUSAGE_THREAD, capture->result_.GetRUsageMonitor());
       capture->notify_->EventFinished(capture->result_);
       capture->ipc_->InternalCleanupFdMap();
-      absl::MutexLock lock(&capture->done_mutex_);
+      capture->done_notification_.Notify();
-      capture->done_.store(true, std::memory_order_release);
     }
     Monitor* capture;
   } monitor_cleanup{this};
@@ -243,7 +240,7 @@ void Monitor::Run() {
 
   // Tell the parent thread (Sandbox2 object) that we're done with the initial
   // set-up process of the sandboxee.
-  decrement_count.reset();
+  setup_notify.reset();
 
   MainLoop(&sigtimedwait_sset);
 }

sandboxed_api/sandbox2/monitor.h

@@ -27,7 +27,7 @@
 #include <ctime>
 #include <memory>
 
-#include "absl/synchronization/blocking_counter.h"
+#include "absl/synchronization/notification.h"
 #include "sandboxed_api/sandbox2/comms.h"
 #include "sandboxed_api/sandbox2/executor.h"
 #include "sandboxed_api/sandbox2/ipc.h"
@@ -60,7 +60,7 @@ class Monitor final {
   void Run();
 
   // Getters for private fields.
-  bool IsDone() const { return done_.load(std::memory_order_acquire); }
+  bool IsDone() const { return done_notification_.HasBeenNotified(); }
 
   // Getter/Setter for wait_for_execve_.
   bool IsActivelyMonitoring();
@@ -156,15 +156,14 @@ class Monitor final {
   // Parent (the Sandbox2 object) waits on it, until we either enable
   // monitoring of a process (sandboxee) successfully, or the setup process
   // fails.
-  absl::BlockingCounter setup_counter_;
+  absl::Notification setup_notification_;
+  // The field indicates whether the sandboxing task has been completed (either
+  // successfully or with error).
+  absl::Notification done_notification_;
 
   // The main tracked PID.
   pid_t pid_ = -1;
 
-  // The field indicates whether the sandboxing task has been completed (either
-  // successfully or with error).
-  std::atomic<bool> done_{false};
-  absl::Mutex done_mutex_;
   // False iff external kill is requested
   std::atomic_flag external_kill_request_flag_;
   // False iff dump stack is requested

sandboxed_api/sandbox2/sandbox2.cc

@@ -21,7 +21,6 @@
 #include <string>
 
 #include "absl/memory/memory.h"
-#include "absl/synchronization/blocking_counter.h"
 #include "sandboxed_api/sandbox2/monitor.h"
 #include "sandboxed_api/sandbox2/result.h"
 #include "sandboxed_api/util/canonical_errors.h"
@@ -39,9 +38,8 @@ sapi::StatusOr<Result> Sandbox2::AwaitResultWithTimeout(
   CHECK(monitor_ != nullptr) << "Sandbox was not launched yet";
   CHECK(monitor_thread_ != nullptr) << "Sandbox was already waited on";
 
-  absl::MutexLock lock(&monitor_->done_mutex_);
+  auto done =
-  auto done = monitor_->done_mutex_.AwaitWithTimeout(
+      monitor_->done_notification_.WaitForNotificationWithTimeout(timeout);
-      absl::Condition(monitor_.get(), &Monitor::IsDone), timeout);
   if (!done) {
     return ::sapi::DeadlineExceededError(
         "Sandbox did not finish within timeout");
@@ -124,7 +122,7 @@ void Sandbox2::Launch() {
   // Wait for the Monitor to set-up the sandboxee correctly (or fail while
   // doing that). From here on, it is safe to use the IPC object for
   // non-sandbox-related data exchange.
-  monitor_->setup_counter_.Wait();
+  monitor_->setup_notification_.WaitForNotification();
 }
 
 }  // namespace sandbox2