From 982f7bd3459e8b260091eba27051ec62bc00b09d Mon Sep 17 00:00:00 2001
From: Josh Gao <jmgao@google.com>
Date: Tue, 12 Feb 2019 13:59:03 -0800
Subject: [PATCH] base: add ScopedLockAssertion.

This is a useful helper for anyone that's using thread safety
annotations alongside std::condition_variable, extract it from adb and
move it to libbase.

Test: mma
Change-Id: Ic51e2f2a0e6a16628034b29d8ff32bf2155afccd
---
 adb/transport.cpp                             | 19 +++-------
 .../include/android-base/thread_annotations.h | 38 +++++++++++++++++++
 2 files changed, 43 insertions(+), 14 deletions(-)

diff --git a/adb/transport.cpp b/adb/transport.cpp
index ae5359794..90f94ee1e 100644
--- a/adb/transport.cpp
+++ b/adb/transport.cpp
@@ -52,6 +52,8 @@
 #include "fdevent.h"
 #include "sysdeps/chrono.h"
 
+using android::base::ScopedLockAssertion;
+
 static void remove_transport(atransport* transport);
 static void transport_unref(atransport* transport);
 
@@ -72,17 +74,6 @@ const char* const kFeatureAbb = "abb";
 
 namespace {
 
-// A class that helps the Clang Thread Safety Analysis deal with
-// std::unique_lock. Given that std::unique_lock is movable, and the analysis
-// can not currently perform alias analysis, it is not annotated. In order to
-// assert that the mutex is held, a ScopedAssumeLocked can be created just after
-// the std::unique_lock.
-class SCOPED_CAPABILITY ScopedAssumeLocked {
-  public:
-    ScopedAssumeLocked(std::mutex& mutex) ACQUIRE(mutex) {}
-    ~ScopedAssumeLocked() RELEASE() {}
-};
-
 #if ADB_HOST
 // Tracks and handles atransport*s that are attempting reconnection.
 class ReconnectHandler {
@@ -180,7 +171,7 @@ void ReconnectHandler::Run() {
         ReconnectAttempt attempt;
         {
             std::unique_lock<std::mutex> lock(reconnect_mutex_);
-            ScopedAssumeLocked assume_lock(reconnect_mutex_);
+            ScopedLockAssertion assume_lock(reconnect_mutex_);
 
             if (!reconnect_queue_.empty()) {
                 // FIXME: libstdc++ (used on Windows) implements condition_variable with
@@ -296,7 +287,7 @@ void BlockingConnectionAdapter::Start() {
         LOG(INFO) << this->transport_name_ << ": write thread spawning";
         while (true) {
             std::unique_lock<std::mutex> lock(mutex_);
-            ScopedAssumeLocked assume_locked(mutex_);
+            ScopedLockAssertion assume_locked(mutex_);
             cv_.wait(lock, [this]() REQUIRES(mutex_) {
                 return this->stopped_ || !this->write_queue_.empty();
             });
@@ -923,7 +914,7 @@ atransport* acquire_one_transport(TransportType type, const char* serial, Transp
 
 bool ConnectionWaitable::WaitForConnection(std::chrono::milliseconds timeout) {
     std::unique_lock<std::mutex> lock(mutex_);
-    ScopedAssumeLocked assume_locked(mutex_);
+    ScopedLockAssertion assume_locked(mutex_);
     return cv_.wait_for(lock, timeout, [&]() REQUIRES(mutex_) {
         return connection_established_ready_;
     }) && connection_established_;
diff --git a/base/include/android-base/thread_annotations.h b/base/include/android-base/thread_annotations.h
index 5c55e6300..53fe6dae9 100644
--- a/base/include/android-base/thread_annotations.h
+++ b/base/include/android-base/thread_annotations.h
@@ -16,6 +16,8 @@
 
 #pragma once
 
+#include <mutex>
+
 #define THREAD_ANNOTATION_ATTRIBUTE__(x) __attribute__((x))
 
 #define CAPABILITY(x) \
@@ -104,3 +106,39 @@
 
 #define NO_THREAD_SAFETY_ANALYSIS \
       THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)
+
+namespace android {
+namespace base {
+
+// A class to help thread safety analysis deal with std::unique_lock and condition_variable.
+//
+// Clang's thread safety analysis currently doesn't perform alias analysis, so movable types
+// like std::unique_lock can't be marked with thread safety annotations. This helper allows
+// for manual assertion of lock state in a scope.
+//
+// For example:
+//
+//   std::mutex mutex;
+//   std::condition_variable cv;
+//   std::vector<int> vec GUARDED_BY(mutex);
+//
+//   int pop() {
+//     std::unique_lock lock(mutex);
+//     ScopedLockAssertion lock_assertion(mutex);
+//     cv.wait(lock, []() {
+//       ScopedLockAssertion lock_assertion(mutex);
+//       return !vec.empty();
+//     });
+//
+//     int result = vec.back();
+//     vec.pop_back();
+//     return result;
+//   }
+class SCOPED_CAPABILITY ScopedLockAssertion {
+ public:
+  ScopedLockAssertion(std::mutex& mutex) ACQUIRE(mutex) {}
+  ~ScopedLockAssertion() RELEASE() {}
+};
+
+}  // namespace base
+}  // namespace android