1 /* Copyright 2019 The TensorFlow Authors. All Rights Reserved.
2 
3 Licensed under the Apache License, Version 2.0 (the "License");
4 you may not use this file except in compliance with the License.
5 You may obtain a copy of the License at
6 
7     http://www.apache.org/licenses/LICENSE-2.0
8 
9 Unless required by applicable law or agreed to in writing, software
10 distributed under the License is distributed on an "AS IS" BASIS,
11 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 See the License for the specific language governing permissions and
13 limitations under the License.
14 ==============================================================================*/
15 
16 #include "tensorflow/compiler/xla/pjrt/semaphore.h"
17 
18 #include "tensorflow/core/platform/logging.h"
19 
20 namespace xla {
21 
Semaphore(int64 capacity)22 Semaphore::Semaphore(int64 capacity) : value_(capacity) {
23   CHECK_GE(capacity, 0);
24 }
25 
CanAcquire(CanAcquireArgs * args)26 bool Semaphore::CanAcquire(CanAcquireArgs* args) {
27   return args->semaphore->value_ >= args->amount;
28 }
29 
Acquire(int64 amount)30 void Semaphore::Acquire(int64 amount) {
31   CHECK_GE(amount, 0);
32 
33   CanAcquireArgs args;
34   args.semaphore = this;
35   args.amount = amount;
36 
37   mu_.LockWhen(absl::Condition(&CanAcquire, &args));
38   value_ -= amount;
39   mu_.Unlock();
40 }
41 
Release(int64 amount)42 void Semaphore::Release(int64 amount) {
43   CHECK_GE(amount, 0);
44   absl::MutexLock lock(&mu_);
45   value_ += amount;
46 }
47 
~ScopedReservation()48 Semaphore::ScopedReservation::~ScopedReservation() {
49   if (semaphore_) {
50     semaphore_->Release(amount_);
51   }
52 }
53 
ScopedReservation(ScopedReservation && other)54 Semaphore::ScopedReservation::ScopedReservation(
55     ScopedReservation&& other) noexcept {
56   semaphore_ = other.semaphore_;
57   amount_ = other.amount_;
58   other.semaphore_ = nullptr;
59 }
60 
operator =(ScopedReservation && other)61 Semaphore::ScopedReservation& Semaphore::ScopedReservation::operator=(
62     ScopedReservation&& other) noexcept {
63   semaphore_ = other.semaphore_;
64   amount_ = other.amount_;
65   other.semaphore_ = nullptr;
66   return *this;
67 }
68 
ScopedAcquire(int64 amount)69 Semaphore::ScopedReservation Semaphore::ScopedAcquire(int64 amount) {
70   Acquire(amount);
71   return ScopedReservation(this, amount);
72 }
73 
74 }  // namespace xla
75