Use absl::Mutex instead of custom implementation (#1356)

Makes `common::Mutex` an alias for `absl::Mutex` and replaces the logic inside `common::MutexLocker` with `absl::MutexLock`.

A future PR can then remove these classes entirely and replace references to it across the Cartographer code base with the Abseil classes directly.

cartographer/BUILD.bazel

@@ -95,7 +95,9 @@ cc_library(
     deps = [
         ":cc_protos",
         "@boost//:iostreams",
+        "@com_google_absl//absl/base",
         "@com_google_absl//absl/types:optional",
+        "@com_google_absl//absl/synchronization",
         "@com_google_glog//:glog",
         "@org_cairographics_cairo//:cairo",
         "@org_ceres_solver_ceres_solver//:ceres",

cartographer/common/mutex.h

@@ -17,83 +17,50 @@
 #ifndef CARTOGRAPHER_COMMON_MUTEX_H_
 #define CARTOGRAPHER_COMMON_MUTEX_H_
 
-#include <condition_variable>
-#include <mutex>
-
+#include "absl/base/thread_annotations.h"
+#include "absl/synchronization/mutex.h"
 #include "cartographer/common/time.h"
 
 namespace cartographer {
 namespace common {
 
-// Enable thread safety attributes only with clang.
-// The attributes can be safely erased when compiling with other compilers.
-#if defined(__SUPPORT_TS_ANNOTATION__) || defined(__clang__)
-#define THREAD_ANNOTATION_ATTRIBUTE__(x) __attribute__((x))
-#else
-#define THREAD_ANNOTATION_ATTRIBUTE__(x)  // no-op
-#endif
-
-#define CAPABILITY(x) THREAD_ANNOTATION_ATTRIBUTE__(capability(x))
-
-#define SCOPED_CAPABILITY THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)
-
-#define GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))
-
-#define PT_GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_by(x))
-
 #define REQUIRES(...) \
   THREAD_ANNOTATION_ATTRIBUTE__(requires_capability(__VA_ARGS__))
 
-#define ACQUIRE(...) \
-  THREAD_ANNOTATION_ATTRIBUTE__(acquire_capability(__VA_ARGS__))
-
-#define RELEASE(...) \
-  THREAD_ANNOTATION_ATTRIBUTE__(release_capability(__VA_ARGS__))
-
 #define EXCLUDES(...) THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(__VA_ARGS__))
 
-#define NO_THREAD_SAFETY_ANALYSIS \
-  THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)
+// TODO(CodeArno): Replace references in code to absl::Mutex directly.
+using Mutex = absl::Mutex;
 
-// Defines an annotated mutex that can only be locked through its scoped locker
-// implementation.
-class CAPABILITY("mutex") Mutex {
+// A RAII class that acquires a mutex in its constructor, and
+// releases it in its destructor. It also implements waiting functionality on
+// conditions that get checked whenever the mutex is released.
+// TODO(CodeArno): Replace MutexLocker instantiations in the codebase with
+// absl::MutexLock.
+class SCOPED_LOCKABLE MutexLocker {
  public:
-  // A RAII class that acquires a mutex in its constructor, and
-  // releases it in its destructor. It also implements waiting functionality on
-  // conditions that get checked whenever the mutex is released.
-  class SCOPED_CAPABILITY Locker {
-   public:
-    Locker(Mutex* mutex) ACQUIRE(mutex) : mutex_(mutex), lock_(mutex->mutex_) {}
+  MutexLocker(Mutex* mutex) EXCLUSIVE_LOCK_FUNCTION(mutex)
+      : mutex_(mutex), lock_(mutex) {}
 
-    ~Locker() RELEASE() {
-      mutex_->condition_.notify_all();
-      lock_.unlock();
-    }
+  ~MutexLocker() UNLOCK_FUNCTION() {}
 
-    template <typename Predicate>
-    void Await(Predicate predicate) REQUIRES(this) {
-      mutex_->condition_.wait(lock_, predicate);
-    }
+  template <typename Predicate>
+  void Await(Predicate predicate) REQUIRES(this) {
+    mutex_->Await(absl::Condition(&predicate));
+  }
 
-    template <typename Predicate>
-    bool AwaitWithTimeout(Predicate predicate, common::Duration timeout)
-        REQUIRES(this) {
-      return mutex_->condition_.wait_for(lock_, timeout, predicate);
-    }
-
-   private:
-    Mutex* mutex_;
-    std::unique_lock<std::mutex> lock_;
-  };
+  template <typename Predicate>
+  bool AwaitWithTimeout(Predicate predicate, common::Duration timeout)
+      REQUIRES(this) {
+    return mutex_->AwaitWithTimeout(absl::Condition(&predicate),
+                                    absl::FromChrono(timeout));
+  }
 
  private:
-  std::condition_variable condition_;
-  std::mutex mutex_;
+  absl::Mutex* mutex_;
+  absl::MutexLock lock_;
 };
 
-using MutexLocker = Mutex::Locker;
-
 }  // namespace common
 }  // namespace cartographer
 

cartographer/common/thread_pool_test.cc

@@ -28,7 +28,7 @@ namespace {
 class Receiver {
  public:
   void Receive(int number) {
-    Mutex::Locker locker(&mutex_);
+    MutexLocker locker(&mutex_);
     received_numbers_.push_back(number);
   }
 

cmake/modules/FindAbseil.cmake

@@ -27,6 +27,8 @@ if(NOT TARGET standalone_absl)
   set(ABSEIL_LIBRARY_PATH
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/synchronization/${prefix}absl_synchronization${suffix}")
   set(ABSEIL_DEPENDENT_LIBRARIES
+    "${ABSEIL_PROJECT_BUILD_DIR}/absl/debugging/${prefix}absl_symbolize${suffix}"
+    "${ABSEIL_PROJECT_BUILD_DIR}/absl/time/${prefix}absl_time${suffix}"
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/algorithm/${prefix}absl_algorithm${suffix}"
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/base/${prefix}absl_base${suffix}"
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/base/${prefix}absl_dynamic_annotations${suffix}"
@@ -41,13 +43,12 @@ if(NOT TARGET standalone_absl)
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/debugging/${prefix}absl_leak_check${suffix}"
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/debugging/${prefix}absl_stack_consumption${suffix}"
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/debugging/${prefix}absl_stacktrace${suffix}"
-    "${ABSEIL_PROJECT_BUILD_DIR}/absl/debugging/${prefix}absl_symbolize${suffix}"
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/memory/${prefix}absl_memory${suffix}"
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/meta/${prefix}absl_meta${suffix}"
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/numeric/${prefix}absl_int128${suffix}"
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/numeric/${prefix}absl_numeric${suffix}"
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/strings/${prefix}absl_strings${suffix}"
-    "${ABSEIL_PROJECT_BUILD_DIR}/absl/time/${prefix}absl_time${suffix}"
+    "${ABSEIL_PROJECT_BUILD_DIR}/absl/synchronization/${prefix}absl_synchronization${suffix}"
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/types/${prefix}absl_any${suffix}"
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/types/${prefix}absl_bad_any_cast${suffix}"
     "${ABSEIL_PROJECT_BUILD_DIR}/absl/types/${prefix}absl_bad_optional_access${suffix}"