thread_quota.h

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// Copyright 2021 gRPC 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.
 
#ifndef GRPC_CORE_LIB_RESOURCE_QUOTA_THREAD_QUOTA_H
#define GRPC_CORE_LIB_RESOURCE_QUOTA_THREAD_QUOTA_H
 
#include <grpc/support/port_platform.h>
 
#include <cstddef>
#include <limits>
 
#include "absl/base/thread_annotations.h"
 
#include "src/core/lib/gprpp/ref_counted.h"
#include "src/core/lib/gprpp/ref_counted_ptr.h"
#include "src/core/lib/gprpp/sync.h"
 
namespace grpc_core {
 
// Tracks the amount of threads in a resource quota.
class ThreadQuota : public RefCounted<ThreadQuota> {
 public:
  ThreadQuota();
  ~ThreadQuota() override;
 
  ThreadQuota(const ThreadQuota&) = delete;
  ThreadQuota& operator=(const ThreadQuota&) = delete;
 
  // Set the maximum number of threads that can be used by this quota.
  // If there are more, new reservations will fail until the quota is available.
  void SetMax(size_t new_max);
 
  // Try to allocate some number of threads.
  // Returns true if the allocation succeeded, false otherwise.
  bool Reserve(size_t num_threads);
 
  // Release some number of threads.
  void Release(size_t num_threads);
 
 private:
  Mutex mu_;
  size_t allocated_ ABSL_GUARDED_BY(mu_) = 0;
  size_t max_ ABSL_GUARDED_BY(mu_) = std::numeric_limits<size_t>::max();
};
 
using ThreadQuotaPtr = RefCountedPtr<ThreadQuota>;
 
}  // namespace grpc_core
 
#endif  // GRPC_CORE_LIB_RESOURCE_QUOTA_THREAD_QUOTA_H