Mutex: Remove destructor in release build

The Mutex destructor is needed only to clean up debug logging
and invariant checking synch events. These are not supposed
to be used in production, but the non-empty destructor has
costs for production builds.

Instead of removing synch events in destructor,
drop all of them if we accumulated too many.
For tests is should not matter (we maybe only consume
a bit more memory). Production builds should be either unaffected
(if don't use debug logging), or use periodic reset of all synch events.

PiperOrigin-RevId: 578123259
Change-Id: I0ec59183a5f63ea0a6b7fc50f0a77974e7f677be

1 files changed, 17 insertions, 1 deletions

diff --git a/absl/synchronization/mutex.h b/absl/synchronization/mutex.h
index 95726f6b..157b7050 100644
--- a/absl/synchronization/mutex.h
+++ b/absl/synchronization/mutex.h
@@ -64,6 +64,7 @@
 #include <iterator>
 #include <string>
 
+#include "absl/base/attributes.h"
 #include "absl/base/const_init.h"
 #include "absl/base/internal/identity.h"
 #include "absl/base/internal/low_level_alloc.h"
@@ -536,6 +537,7 @@ class ABSL_LOCKABLE Mutex {
   void Block(base_internal::PerThreadSynch* s);
   // Wake a thread; return successor.
   base_internal::PerThreadSynch* Wakeup(base_internal::PerThreadSynch* w);
+  void Dtor();
 
   friend class CondVar;   // for access to Trans()/Fer().
   void Trans(MuHow how);  // used for CondVar->Mutex transfer
@@ -909,7 +911,6 @@ class CondVar {
   // A `CondVar` allocated on the heap or on the stack can use the this
   // constructor.
   CondVar();
-  ~CondVar();
 
   // CondVar::Wait()
   //
@@ -1061,6 +1062,21 @@ inline Mutex::Mutex() : mu_(0) {
 
 inline constexpr Mutex::Mutex(absl::ConstInitType) : mu_(0) {}
 
+#if !defined(__APPLE__) && !defined(ABSL_BUILD_DLL)
+ABSL_ATTRIBUTE_ALWAYS_INLINE
+inline Mutex::~Mutex() { Dtor(); }
+#endif
+
+#if defined(NDEBUG) && !defined(ABSL_HAVE_THREAD_SANITIZER)
+// Use default (empty) destructor in release build for performance reasons.
+// We need to mark both Dtor and ~Mutex as always inline for inconsistent
+// builds that use both NDEBUG and !NDEBUG with dynamic libraries. In these
+// cases we want the empty functions to dissolve entirely rather than being
+// exported from dynamic libraries and potentially override the non-empty ones.
+ABSL_ATTRIBUTE_ALWAYS_INLINE
+inline void Mutex::Dtor() {}
+#endif
+
 inline CondVar::CondVar() : cv_(0) {}
 
 // static