From 2fc37573b9a0a6dbabee66056d420737565c58ec Mon Sep 17 00:00:00 2001
From: Tommi <tommi@webrtc.org>
Date: Mon, 24 Oct 2022 09:22:16 +0200
Subject: [PATCH] Add DISALLOW_WAIT(), a regression catching utility.

Bug: none
Change-Id: I94def80a7eb815f74d1be691d21b5f3661771a71
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/279821
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Evan Shrubsole <eshr@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38457}
---
 rtc_base/event.h           | 45 ++++++++++++++++++++++++++++++++++++++
 rtc_base/event_unittest.cc | 10 +++++++++
 2 files changed, 55 insertions(+)

diff --git a/rtc_base/event.h b/rtc_base/event.h
index 941497ca7b..12f6a7dca2 100644
--- a/rtc_base/event.h
+++ b/rtc_base/event.h
@@ -12,6 +12,7 @@
 #define RTC_BASE_EVENT_H_
 
 #include "api/units/time_delta.h"
+
 #if defined(WEBRTC_WIN)
 #include <windows.h>
 #elif defined(WEBRTC_POSIX)
@@ -20,8 +21,38 @@
 #error "Must define either WEBRTC_WIN or WEBRTC_POSIX."
 #endif
 
+#include "rtc_base/synchronization/yield_policy.h"
+
 namespace rtc {
 
+// RTC_DISALLOW_WAIT() utility
+//
+// Sets a stack-scoped flag that disallows use of `rtc::Event::Wait` by means
+// of raising a DCHECK when a call to `rtc::Event::Wait()` is made..
+// This is useful to guard synchronization-free scopes against regressions.
+//
+// Example of what this would catch (`ScopeToProtect` calls `Foo`):
+//
+//  void Foo(TaskQueue* tq) {
+//    Event event;
+//    tq->PostTask([&event]() {
+//      event.Set();
+//    });
+//    event.Wait(Event::kForever);  // <- Will trigger a DCHECK.
+//  }
+//
+//  void ScopeToProtect() {
+//    TaskQueue* tq = GetSomeTaskQueue();
+//    RTC_DISALLOW_WAIT();  // Policy takes effect.
+//    Foo(tq);
+//  }
+//
+#if RTC_DCHECK_IS_ON
+#define RTC_DISALLOW_WAIT() ScopedDisallowWait disallow_wait_##__LINE__
+#else
+#define RTC_DISALLOW_WAIT()
+#endif
+
 class Event {
  public:
   // TODO(bugs.webrtc.org/14366): Consider removing this redundant alias.
@@ -87,6 +118,20 @@ class ScopedAllowBaseSyncPrimitivesForTesting {
   ~ScopedAllowBaseSyncPrimitivesForTesting() {}
 };
 
+#if RTC_DCHECK_IS_ON
+class ScopedDisallowWait {
+ public:
+  ScopedDisallowWait() = default;
+
+ private:
+  class DisallowYieldHandler : public YieldInterface {
+   public:
+    void YieldExecution() override { RTC_DCHECK_NOTREACHED(); }
+  } handler_;
+  rtc::ScopedYieldPolicy policy{&handler_};
+};
+#endif
+
 }  // namespace rtc
 
 #endif  // RTC_BASE_EVENT_H_
diff --git a/rtc_base/event_unittest.cc b/rtc_base/event_unittest.cc
index e35373142e..17f50dc2d1 100644
--- a/rtc_base/event_unittest.cc
+++ b/rtc_base/event_unittest.cc
@@ -102,4 +102,14 @@ TEST(EventTest, DISABLED_PerformanceMultiThread) {
   thread.Stop();
 }
 
+#if RTC_DCHECK_IS_ON && GTEST_HAS_DEATH_TEST && !defined(WEBRTC_ANDROID)
+// Tests that we crash if we attempt to call rtc::Event::Wait while we're
+// not allowed to (as per `RTC_DISALLOW_WAIT()`).
+TEST(EventTestDeathTest, DisallowEventWait) {
+  Event event;
+  RTC_DISALLOW_WAIT();
+  EXPECT_DEATH(event.Wait(Event::kForever), "");
+}
+#endif  // RTC_DCHECK_IS_ON && GTEST_HAS_DEATH_TEST && !defined(WEBRTC_ANDROID)
+
 }  // namespace rtc