1 files changed, 106 insertions, 0 deletions
diff --git a/absl/synchronization/internal/per_thread_sem.cc b/absl/synchronization/internal/per_thread_sem.cc
new file mode 100644
index 000000000000..af87222816d5
--- /dev/null
+++ b/absl/synchronization/internal/per_thread_sem.cc
@@ -0,0 +1,106 @@
+// 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.
+
+// This file is a no-op if the required LowLevelAlloc support is missing.
+#include "absl/base/internal/low_level_alloc.h"
+#ifndef ABSL_LOW_LEVEL_ALLOC_MISSING
+
+#include "absl/synchronization/internal/per_thread_sem.h"
+
+#include <atomic>
+
+#include "absl/base/attributes.h"
+#include "absl/base/internal/malloc_extension.h"
+#include "absl/base/internal/thread_identity.h"
+#include "absl/synchronization/internal/waiter.h"
+
+namespace absl {
+namespace synchronization_internal {
+
+void PerThreadSem::SetThreadBlockedCounter(std::atomic<int> *counter) {
+  base_internal::ThreadIdentity *identity;
+  identity = GetOrCreateCurrentThreadIdentity();
+  identity->blocked_count_ptr = counter;
+}
+
+std::atomic<int> *PerThreadSem::GetThreadBlockedCounter() {
+  base_internal::ThreadIdentity *identity;
+  identity = GetOrCreateCurrentThreadIdentity();
+  return identity->blocked_count_ptr;
+}
+
+void PerThreadSem::Init(base_internal::ThreadIdentity *identity) {
+  Waiter::GetWaiter(identity)->Init();
+  identity->ticker.store(0, std::memory_order_relaxed);
+  identity->wait_start.store(0, std::memory_order_relaxed);
+  identity->is_idle.store(false, std::memory_order_relaxed);
+}
+
+void PerThreadSem::Tick(base_internal::ThreadIdentity *identity) {
+  const int ticker =
+      identity->ticker.fetch_add(1, std::memory_order_relaxed) + 1;
+  const int wait_start = identity->wait_start.load(std::memory_order_relaxed);
+  const bool is_idle = identity->is_idle.load(std::memory_order_relaxed);
+  if (wait_start && (ticker - wait_start > Waiter::kIdlePeriods) && !is_idle) {
+    // Wakeup the waiting thread since it is time for it to become idle.
+    Waiter::GetWaiter(identity)->Poke();
+  }
+}
+
+}  // namespace synchronization_internal
+}  // namespace absl
+
+extern "C" {
+
+ABSL_ATTRIBUTE_WEAK void AbslInternalPerThreadSemPost(
+    absl::base_internal::ThreadIdentity *identity) {
+  absl::synchronization_internal::Waiter::GetWaiter(identity)->Post();
+}
+
+ABSL_ATTRIBUTE_WEAK bool AbslInternalPerThreadSemWait(
+    absl::synchronization_internal::KernelTimeout t) {
+  bool timeout = false;
+  absl::base_internal::ThreadIdentity *identity;
+  identity = absl::synchronization_internal::GetOrCreateCurrentThreadIdentity();
+
+  // Ensure wait_start != 0.
+  int ticker = identity->ticker.load(std::memory_order_relaxed);
+  identity->wait_start.store(ticker ? ticker : 1, std::memory_order_relaxed);
+  identity->is_idle.store(false, std::memory_order_relaxed);
+
+  if (identity->blocked_count_ptr != nullptr) {
+    // Increment count of threads blocked in a given thread pool.
+    identity->blocked_count_ptr->fetch_add(1, std::memory_order_relaxed);
+  }
+
+  timeout =
+      !absl::synchronization_internal::Waiter::GetWaiter(identity)->Wait(t);
+
+  if (identity->blocked_count_ptr != nullptr) {
+    identity->blocked_count_ptr->fetch_sub(1, std::memory_order_relaxed);
+  }
+
+  if (identity->is_idle.load(std::memory_order_relaxed)) {
+    // We became idle during the wait; become non-idle again so that
+    // performance of deallocations done from now on does not suffer.
+    absl::base_internal::MallocExtension::instance()->MarkThreadBusy();
+  }
+  identity->is_idle.store(false, std::memory_order_relaxed);
+  identity->wait_start.store(0, std::memory_order_relaxed);
+  return !timeout;
+}
+
+}  // extern "C"
+
+#endif  // ABSL_LOW_LEVEL_ALLOC_MISSING