- 45b4111d940009bc7b3ebf621c9cb9293c60344a Use copied value i in lambda by Abseil Team <absl-team@google.com>

  - b726b3102f8439b8480b6ff52fc3660162fa0bd9 Fix MSVC compiler warning on 32-bit platforms (GitHub iss... by Derek Mauro <dmauro@google.com>
  - a8a29e636c85bd7d82c0cbc824a1c2e498764337 Explicitly forbid to specify the template parameter to Wr... by Abseil Team <absl-team@google.com>
  - 566a1d903266fdbfdcf758401c356a0c6703422d Add missing license header to BUILD file. by Alex Strelnikov <strel@google.com>
  - ef1c0642cde0bbad62bbb30715256b232a4ab817 Fix BUILD file header. by Alex Strelnikov <strel@google.com>
  - b6e2cf00f808ee32b9eb7b3226af79d628742c20 Release GraphCycles microbenchmark. by Alex Strelnikov <strel@google.com>
  - f592d78f549e7a242bf2bb4858a26645a655eac3 Release Mutex microbenchmarks. by Alex Strelnikov <strel@google.com>

GitOrigin-RevId: 45b4111d940009bc7b3ebf621c9cb9293c60344a
Change-Id: I82885ae176952a764574c6d4616e312a977407b2

5 files changed, 188 insertions, 30 deletions

diff --git a/absl/synchronization/BUILD.bazel b/absl/synchronization/BUILD.bazel
index 05376903..67ce7ff9 100644
--- a/absl/synchronization/BUILD.bazel
+++ b/absl/synchronization/BUILD.bazel
@@ -39,6 +39,7 @@ cc_library(
     ],
     deps = [
         "//absl/base",
+        "//absl/base:base_internal",
         "//absl/base:core_headers",
         "//absl/base:malloc_internal",
     ],
@@ -119,6 +120,20 @@ cc_test(
     ],
 )
 
+cc_test(
+    name = "graphcycles_benchmark",
+    srcs = ["internal/graphcycles_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = [
+        "benchmark",
+    ],
+    deps = [
+        ":graphcycles_internal",
+        "//absl/base",
+        "@com_github_google_benchmark//:benchmark",
+    ],
+)
+
 cc_library(
     name = "thread_pool",
     testonly = 1,
@@ -149,6 +164,20 @@ cc_test(
 )
 
 cc_test(
+    name = "mutex_benchmark",
+    srcs = ["mutex_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":synchronization",
+        ":thread_pool",
+        "//absl/base",
+        "@com_github_google_benchmark//:benchmark",
+    ],
+)
+
+cc_test(
     name = "notification_test",
     size = "small",
     srcs = ["notification_test.cc"],
diff --git a/absl/synchronization/internal/graphcycles.cc b/absl/synchronization/internal/graphcycles.cc
index 28ad172c..ab1f3f84 100644
--- a/absl/synchronization/internal/graphcycles.cc
+++ b/absl/synchronization/internal/graphcycles.cc
@@ -37,6 +37,7 @@
 
 #include <algorithm>
 #include <array>
+#include "absl/base/internal/hide_ptr.h"
 #include "absl/base/internal/raw_logging.h"
 #include "absl/base/internal/spinlock.h"
 
@@ -276,18 +277,6 @@ inline uint32_t NodeVersion(GraphId id) {
   return static_cast<uint32_t>(id.handle >> 32);
 }
 
-// We need to hide Mutexes (or other deadlock detection's pointers)
-// from the leak detector.  Xor with an arbitrary number with high bits set.
-static const uintptr_t kHideMask = static_cast<uintptr_t>(0xF03A5F7BF03A5F7Bll);
-
-static inline uintptr_t MaskPtr(void *ptr) {
-  return reinterpret_cast<uintptr_t>(ptr) ^ kHideMask;
-}
-
-static inline void* UnmaskPtr(uintptr_t word) {
-  return reinterpret_cast<void*>(word ^ kHideMask);
-}
-
 struct Node {
   int32_t rank;               // rank number assigned by Pearce-Kelly algorithm
   uint32_t version;           // Current version number
@@ -309,7 +298,7 @@ class PointerMap {
   }
 
   int32_t Find(void* ptr) {
-    auto masked = MaskPtr(ptr);
+    auto masked = base_internal::HidePtr(ptr);
     for (int32_t i = table_[Hash(ptr)]; i != -1;) {
       Node* n = (*nodes_)[i];
       if (n->masked_ptr == masked) return i;
@@ -327,7 +316,7 @@ class PointerMap {
   int32_t Remove(void* ptr) {
     // Advance through linked list while keeping track of the
     // predecessor slot that points to the current entry.
-    auto masked = MaskPtr(ptr);
+    auto masked = base_internal::HidePtr(ptr);
     for (int32_t* slot = &table_[Hash(ptr)]; *slot != -1; ) {
       int32_t index = *slot;
       Node* n = (*nodes_)[index];
@@ -395,7 +384,7 @@ bool GraphCycles::CheckInvariants() const {
   NodeSet ranks;  // Set of ranks seen so far.
   for (uint32_t x = 0; x < r->nodes_.size(); x++) {
     Node* nx = r->nodes_[x];
-    void* ptr = UnmaskPtr(nx->masked_ptr);
+    void* ptr = base_internal::UnhidePtr<void>(nx->masked_ptr);
     if (ptr != nullptr && static_cast<uint32_t>(r->ptrmap_.Find(ptr)) != x) {
       ABSL_RAW_LOG(FATAL, "Did not find live node in hash table %u %p", x, ptr);
     }
@@ -427,7 +416,7 @@ GraphId GraphCycles::GetId(void* ptr) {
     n->version = 1;  // Avoid 0 since it is used by InvalidGraphId()
     n->visited = false;
     n->rank = rep_->nodes_.size();
-    n->masked_ptr = MaskPtr(ptr);
+    n->masked_ptr = base_internal::HidePtr(ptr);
     n->nstack = 0;
     n->priority = 0;
     rep_->nodes_.push_back(n);
@@ -439,7 +428,7 @@ GraphId GraphCycles::GetId(void* ptr) {
     int32_t r = rep_->free_nodes_.back();
     rep_->free_nodes_.pop_back();
     Node* n = rep_->nodes_[r];
-    n->masked_ptr = MaskPtr(ptr);
+    n->masked_ptr = base_internal::HidePtr(ptr);
     n->nstack = 0;
     n->priority = 0;
     rep_->ptrmap_.Add(ptr, r);
@@ -461,7 +450,7 @@ void GraphCycles::RemoveNode(void* ptr) {
   }
   x->in.clear();
   x->out.clear();
-  x->masked_ptr = MaskPtr(nullptr);
+  x->masked_ptr = base_internal::HidePtr<void>(nullptr);
   if (x->version == std::numeric_limits<uint32_t>::max()) {
     // Cannot use x any more
   } else {
@@ -472,7 +461,8 @@ void GraphCycles::RemoveNode(void* ptr) {
 
 void* GraphCycles::Ptr(GraphId id) {
   Node* n = FindNode(rep_, id);
-  return n == nullptr ? nullptr : UnmaskPtr(n->masked_ptr);
+  return n == nullptr ? nullptr
+                      : base_internal::UnhidePtr<void>(n->masked_ptr);
 }
 
 bool GraphCycles::HasNode(GraphId node) {
diff --git a/absl/synchronization/internal/graphcycles_benchmark.cc b/absl/synchronization/internal/graphcycles_benchmark.cc
new file mode 100644
index 00000000..b4a1debe
--- /dev/null
+++ b/absl/synchronization/internal/graphcycles_benchmark.cc
@@ -0,0 +1,46 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/synchronization/internal/graphcycles.h"
+
+#include <algorithm>
+#include <cstdint>
+#include <vector>
+
+#include "benchmark/benchmark.h"
+#include "absl/base/internal/raw_logging.h"
+
+namespace {
+
+void BM_StressTest(benchmark::State& state) {
+  const int num_nodes = state.range(0);
+  while (state.KeepRunningBatch(num_nodes)) {
+    absl::synchronization_internal::GraphCycles g;
+    std::vector<absl::synchronization_internal::GraphId> nodes(num_nodes);
+    for (int i = 0; i < num_nodes; i++) {
+      nodes[i] = g.GetId(reinterpret_cast<void*>(static_cast<uintptr_t>(i)));
+    }
+    for (int i = 0; i < num_nodes; i++) {
+      int end = std::min(num_nodes, i + 5);
+      for (int j = i + 1; j < end; j++) {
+        ABSL_RAW_CHECK(g.InsertEdge(nodes[i], nodes[j]), "");
+      }
+    }
+  }
+}
+BENCHMARK(BM_StressTest)->Range(2048, 1048576);
+
+}  // namespace
+
+BENCHMARK_MAIN();
diff --git a/absl/synchronization/mutex.cc b/absl/synchronization/mutex.cc
index bd54a4dc..e6525046 100644
--- a/absl/synchronization/mutex.cc
+++ b/absl/synchronization/mutex.cc
@@ -43,6 +43,7 @@
 #include "absl/base/dynamic_annotations.h"
 #include "absl/base/internal/atomic_hook.h"
 #include "absl/base/internal/cycleclock.h"
+#include "absl/base/internal/hide_ptr.h"
 #include "absl/base/internal/low_level_alloc.h"
 #include "absl/base/internal/raw_logging.h"
 #include "absl/base/internal/spinlock.h"
@@ -272,13 +273,6 @@ static absl::base_internal::SpinLock synch_event_mu(
 // Can't be too small, as it's used for deadlock detection information.
 static const uint32_t kNSynchEvent = 1031;
 
-// We need to hide Mutexes (or other deadlock detection's pointers)
-// from the leak detector.
-static const uintptr_t kHideMask = static_cast<uintptr_t>(0xF03A5F7BF03A5F7BLL);
-static uintptr_t MaskMu(const void *mu) {
-  return reinterpret_cast<uintptr_t>(mu) ^ kHideMask;
-}
-
 static struct SynchEvent {     // this is a trivial hash table for the events
   // struct is freed when refcount reaches 0
   int refcount GUARDED_BY(synch_event_mu);
@@ -314,7 +308,8 @@ static SynchEvent *EnsureSynchEvent(std::atomic<intptr_t> *addr,
   SynchEvent *e;
   // first look for existing SynchEvent struct..
   synch_event_mu.Lock();
-  for (e = synch_event[h]; e != nullptr && e->masked_addr != MaskMu(addr);
+  for (e = synch_event[h];
+       e != nullptr && e->masked_addr != base_internal::HidePtr(addr);
        e = e->next) {
   }
   if (e == nullptr) {  // no SynchEvent struct found; make one.
@@ -325,7 +320,7 @@ static SynchEvent *EnsureSynchEvent(std::atomic<intptr_t> *addr,
     e = reinterpret_cast<SynchEvent *>(
         base_internal::LowLevelAlloc::Alloc(sizeof(*e) + l));
     e->refcount = 2;    // one for return value, one for linked list
-    e->masked_addr = MaskMu(addr);
+    e->masked_addr = base_internal::HidePtr(addr);
     e->invariant = nullptr;
     e->arg = nullptr;
     e->log = false;
@@ -367,7 +362,8 @@ static void ForgetSynchEvent(std::atomic<intptr_t> *addr, intptr_t bits,
   SynchEvent *e;
   synch_event_mu.Lock();
   for (pe = &synch_event[h];
-       (e = *pe) != nullptr && e->masked_addr != MaskMu(addr); pe = &e->next) {
+       (e = *pe) != nullptr && e->masked_addr != base_internal::HidePtr(addr);
+       pe = &e->next) {
   }
   bool del = false;
   if (e != nullptr) {
@@ -388,7 +384,8 @@ static SynchEvent *GetSynchEvent(const void *addr) {
   uint32_t h = reinterpret_cast<intptr_t>(addr) % kNSynchEvent;
   SynchEvent *e;
   synch_event_mu.Lock();
-  for (e = synch_event[h]; e != nullptr && e->masked_addr != MaskMu(addr);
+  for (e = synch_event[h];
+       e != nullptr && e->masked_addr != base_internal::HidePtr(addr);
        e = e->next) {
   }
   if (e != nullptr) {
diff --git a/absl/synchronization/mutex_benchmark.cc b/absl/synchronization/mutex_benchmark.cc
new file mode 100644
index 00000000..d91071b7
--- /dev/null
+++ b/absl/synchronization/mutex_benchmark.cc
@@ -0,0 +1,96 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <vector>
+
+#include "benchmark/benchmark.h"
+#include "absl/base/internal/sysinfo.h"
+#include "absl/synchronization/blocking_counter.h"
+#include "absl/synchronization/internal/thread_pool.h"
+#include "absl/synchronization/mutex.h"
+
+namespace {
+
+// Measure the overhead of conditions on mutex release (when they must be
+// evaluated).  Mutex has (some) support for equivalence classes allowing
+// Conditions with the same function/argument to potentially not be multiply
+// evaluated.
+//
+// num_classes==0 is used for the special case of every waiter being distinct.
+void BM_ConditionWaiters(benchmark::State& state) {
+  int num_classes = state.range(0);
+  int num_waiters = state.range(1);
+
+  struct Helper {
+    static void Waiter(absl::BlockingCounter* init, absl::Mutex* m, int* p) {
+      init->DecrementCount();
+      m->LockWhen(absl::Condition(
+          static_cast<bool (*)(int*)>([](int* v) { return *v == 0; }), p));
+      m->Unlock();
+    }
+  };
+
+  if (num_classes == 0) {
+    // No equivalence classes.
+    num_classes = num_waiters;
+  }
+
+  absl::BlockingCounter init(num_waiters);
+  absl::Mutex mu;
+  std::vector<int> equivalence_classes(num_classes, 1);
+
+  // Must be declared last to be destroyed first.
+  absl::synchronization_internal::ThreadPool pool(num_waiters);
+
+  for (int i = 0; i < num_waiters; i++) {
+    // Mutex considers Conditions with the same function and argument
+    // to be equivalent.
+    pool.Schedule([&, i] {
+      Helper::Waiter(&init, &mu, &equivalence_classes[i % num_classes]);
+    });
+  }
+  init.Wait();
+
+  for (auto _ : state) {
+    mu.Lock();
+    mu.Unlock();  // Each unlock requires Condition evaluation for our waiters.
+  }
+
+  mu.Lock();
+  for (int i = 0; i < num_classes; i++) {
+    equivalence_classes[i] = 0;
+  }
+  mu.Unlock();
+}
+
+#ifdef THREAD_SANITIZER
+// ThreadSanitizer can't handle 8192 threads.
+constexpr int kMaxConditionWaiters = 2048;
+#else
+constexpr int kMaxConditionWaiters = 8192;
+#endif
+BENCHMARK(BM_ConditionWaiters)->RangePair(0, 2, 1, kMaxConditionWaiters);
+
+void BM_ContendedMutex(benchmark::State& state) {
+  static absl::Mutex* mu = new absl::Mutex;
+  for (auto _ : state) {
+    absl::MutexLock lock(mu);
+  }
+}
+BENCHMARK(BM_ContendedMutex)->Threads(1);
+BENCHMARK(BM_ContendedMutex)->ThreadPerCpu();
+
+}  // namespace
+
+BENCHMARK_MAIN();