Expose ThreadPool under include/rocksdb/threadpool.h

Summary:
This diff split ThreadPool to
-ThreadPool (abstract interface exposed in include/rocksdb/threadpool.h)
-ThreadPoolImpl (actual implementation in util/threadpool_imp.h)

This allow us to expose ThreadPool to the user so we can use it as an option later

Test Plan: existing unit tests

Reviewers: andrewkr, yiwu, yhchiang, sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D62085

CMakeLists.txt

@@ -240,7 +240,7 @@ set(SOURCES
         util/testharness.cc
         util/testutil.cc
         util/thread_local.cc
-        util/threadpool.cc
+        util/threadpool_imp.cc
         util/thread_status_impl.cc
         util/thread_status_updater.cc
         util/thread_status_util.cc

include/rocksdb/threadpool.h

@@ -0,0 +1,37 @@
+//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under the BSD-style license found in the
+//  LICENSE file in the root directory of this source tree. An additional grant
+//  of patent rights can be found in the PATENTS file in the same directory.
+//
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+#pragma once
+
+namespace rocksdb {
+
+/*
+ * ThreadPool is a component that will spawn N background threads that will
+ * be used to execute scheduled work, The number of background threads could
+ * be modified by calling SetBackgroundThreads().
+ * */
+class ThreadPool {
+ public:
+  virtual ~ThreadPool() {}
+
+  // Wait for all threads to finish.
+  virtual void JoinAllThreads() = 0;
+
+  // Set the number of background threads that will be executing the
+  // scheduled jobs.
+  virtual void SetBackgroundThreads(int num) = 0;
+
+  // Get the number of jobs scheduled in the ThreadPool queue.
+  virtual unsigned int GetQueueLen() const = 0;
+};
+
+// NewThreadPool() is a function that could be used to create a ThreadPool
+// with `num_threads` background threads.
+extern ThreadPool* NewThreadPool(int num_threads);
+
+}  // namespace rocksdb

port/win/env_win.h

@@ -17,7 +17,7 @@
 #pragma once
 
 #include <rocksdb/env.h>
-#include "util/threadpool.h"
+#include "util/threadpool_imp.h"
 
 #include <mutex>
 #include <vector>
@@ -63,7 +63,7 @@ private:
 
   Env*                     hosted_env_;
   mutable std::mutex       mu_;
-  std::vector<ThreadPool>  thread_pools_;
+  std::vector<ThreadPoolImpl> thread_pools_;
   std::vector<std::thread> threads_to_join_;
 
 };
@@ -269,7 +269,6 @@ private:
 
   WinEnvIO      winenv_io_;
   WinEnvThreads winenv_threads_;
-
 };
 
 }

src.mk

@@ -110,7 +110,7 @@ LIB_SOURCES =                                                   \
   util/iostats_context.cc                                       \
   util/io_posix.cc                                              \
   util/lru_cache.cc                                             \
-  util/threadpool.cc                                            \
+  util/threadpool_imp.cc                                        \
   util/transaction_test_util.cc                                 \
 	util/sharded_cache.cc       																	\
   util/sst_file_manager_impl.cc                                 \

util/env_posix.cc

@@ -42,7 +42,6 @@
 #include "rocksdb/slice.h"
 #include "util/coding.h"
 #include "util/io_posix.h"
-#include "util/threadpool.h"
 #include "util/iostats_context_imp.h"
 #include "util/logging.h"
 #include "util/posix_logger.h"
@@ -51,6 +50,7 @@
 #include "util/sync_point.h"
 #include "util/thread_local.h"
 #include "util/thread_status_updater.h"
+#include "util/threadpool_imp.h"
 
 #if !defined(TMPFS_MAGIC)
 #define TMPFS_MAGIC 0x01021994
@@ -739,7 +739,7 @@ class PosixEnv : public Env {
 
   size_t page_size_;
 
-  std::vector<ThreadPool> thread_pools_;
+  std::vector<ThreadPoolImpl> thread_pools_;
   pthread_mutex_t mu_;
   std::vector<pthread_t> threads_to_join_;
 };
@@ -749,7 +749,7 @@ PosixEnv::PosixEnv()
       forceMmapOff(false),
       page_size_(getpagesize()),
       thread_pools_(Priority::TOTAL) {
-  ThreadPool::PthreadCall("mutex_init", pthread_mutex_init(&mu_, nullptr));
+  ThreadPoolImpl::PthreadCall("mutex_init", pthread_mutex_init(&mu_, nullptr));
   for (int pool_id = 0; pool_id < Env::Priority::TOTAL; ++pool_id) {
     thread_pools_[pool_id].SetThreadPriority(
         static_cast<Env::Priority>(pool_id));
@@ -791,11 +791,11 @@ void PosixEnv::StartThread(void (*function)(void* arg), void* arg) {
   StartThreadState* state = new StartThreadState;
   state->user_function = function;
   state->arg = arg;
-  ThreadPool::PthreadCall(
+  ThreadPoolImpl::PthreadCall(
       "start thread", pthread_create(&t, nullptr, &StartThreadWrapper, state));
-  ThreadPool::PthreadCall("lock", pthread_mutex_lock(&mu_));
+  ThreadPoolImpl::PthreadCall("lock", pthread_mutex_lock(&mu_));
   threads_to_join_.push_back(t);
-  ThreadPool::PthreadCall("unlock", pthread_mutex_unlock(&mu_));
+  ThreadPoolImpl::PthreadCall("unlock", pthread_mutex_unlock(&mu_));
 }
 
 void PosixEnv::WaitForJoin() {

util/threadpool_imp.cc

@@ -7,9 +7,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
-#include "util/threadpool.h"
+#include "util/threadpool_imp.h"
-#include <atomic>
 #include <algorithm>
+#include <atomic>
 
 #ifndef OS_WIN
 #  include <unistd.h>
@@ -26,7 +26,7 @@
 
 namespace rocksdb {
 
-void ThreadPool::PthreadCall(const char* label, int result) {
+void ThreadPoolImpl::PthreadCall(const char* label, int result) {
   if (result != 0) {
     fprintf(stderr, "pthread %s: %s\n", label, strerror(result));
     abort();
@@ -38,7 +38,7 @@ namespace {
 
 struct Lock {
   std::unique_lock<std::mutex> ul_;
-  Lock(std::mutex& m) : ul_(m, std::defer_lock) {}
+  explicit Lock(const std::mutex& m) : ul_(m, std::defer_lock) {}
 };
 
 using Condition = std::condition_variable;
@@ -124,7 +124,7 @@ int ThreadDetach(pthread_t& thread) {
 #endif
 }
 
-ThreadPool::ThreadPool()
+ThreadPoolImpl::ThreadPoolImpl()
     : total_threads_limit_(1),
       bgthreads_(0),
       queue_(),
@@ -138,10 +138,9 @@ ThreadPool::ThreadPool()
 #endif
 }
 
-ThreadPool::~ThreadPool() { assert(bgthreads_.size() == 0U); }
+ThreadPoolImpl::~ThreadPoolImpl() { assert(bgthreads_.size() == 0U); }
-
-void ThreadPool::JoinAllThreads() {
 
+void ThreadPoolImpl::JoinAllThreads() {
   Lock lock(mu_);
   PthreadCall("lock", ThreadPoolMutexLock(lock));
   assert(!exit_all_threads_);
@@ -156,7 +155,7 @@ void ThreadPool::JoinAllThreads() {
   bgthreads_.clear();
 }
 
-void ThreadPool::LowerIOPriority() {
+void ThreadPoolImpl::LowerIOPriority() {
 #ifdef OS_LINUX
   PthreadCall("lock", pthread_mutex_lock(&mu_));
   low_io_priority_ = true;
@@ -164,7 +163,7 @@ void ThreadPool::LowerIOPriority() {
 #endif
 }
 
-void ThreadPool::BGThread(size_t thread_id) {
+void ThreadPoolImpl::BGThread(size_t thread_id) {
   bool low_io_priority = false;
   while (true) {
 // Wait until there is an item that is ready to run
@@ -233,16 +232,16 @@ void ThreadPool::BGThread(size_t thread_id) {
 
 // Helper struct for passing arguments when creating threads.
 struct BGThreadMetadata {
-  ThreadPool* thread_pool_;
+  ThreadPoolImpl* thread_pool_;
   size_t thread_id_;  // Thread count in the thread.
-  BGThreadMetadata(ThreadPool* thread_pool, size_t thread_id)
+  BGThreadMetadata(ThreadPoolImpl* thread_pool, size_t thread_id)
       : thread_pool_(thread_pool), thread_id_(thread_id) {}
 };
 
 static void* BGThreadWrapper(void* arg) {
   BGThreadMetadata* meta = reinterpret_cast<BGThreadMetadata*>(arg);
   size_t thread_id = meta->thread_id_;
-  ThreadPool* tp = meta->thread_pool_;
+  ThreadPoolImpl* tp = meta->thread_pool_;
 #if ROCKSDB_USING_THREAD_STATUS
   // for thread-status
   ThreadStatusUtil::RegisterThread(
@@ -258,11 +257,11 @@ static void* BGThreadWrapper(void* arg) {
   return nullptr;
 }
 
-void ThreadPool::WakeUpAllThreads() {
+void ThreadPoolImpl::WakeUpAllThreads() {
   PthreadCall("signalall", ConditionSignalAll(bgsignal_));
 }
 
-void ThreadPool::SetBackgroundThreadsInternal(int num, bool allow_reduce) {
+void ThreadPoolImpl::SetBackgroundThreadsInternal(int num, bool allow_reduce) {
   Lock lock(mu_);
   PthreadCall("lock", ThreadPoolMutexLock(lock));
   if (exit_all_threads_) {
@@ -278,15 +277,15 @@ void ThreadPool::SetBackgroundThreadsInternal(int num, bool allow_reduce) {
   PthreadCall("unlock", MutexUnlock(lock));
 }
 
-void ThreadPool::IncBackgroundThreadsIfNeeded(int num) {
+void ThreadPoolImpl::IncBackgroundThreadsIfNeeded(int num) {
   SetBackgroundThreadsInternal(num, false);
 }
 
-void ThreadPool::SetBackgroundThreads(int num) {
+void ThreadPoolImpl::SetBackgroundThreads(int num) {
   SetBackgroundThreadsInternal(num, true);
 }
 
-void ThreadPool::StartBGThreads() {
+void ThreadPoolImpl::StartBGThreads() {
   // Start background thread if necessary
   while ((int)bgthreads_.size() < total_threads_limit_) {
 #ifdef ROCKSDB_STD_THREADPOOL
@@ -313,9 +312,8 @@ void ThreadPool::StartBGThreads() {
   }
 }
 
-void ThreadPool::Schedule(void (*function)(void* arg1), void* arg, void* tag,
+void ThreadPoolImpl::Schedule(void (*function)(void* arg1), void* arg,
-                          void (*unschedFunction)(void* arg)) {
+                              void* tag, void (*unschedFunction)(void* arg)) {
-
   Lock lock(mu_);
   PthreadCall("lock", ThreadPoolMutexLock(lock));
 
@@ -347,7 +345,7 @@ void ThreadPool::Schedule(void (*function)(void* arg1), void* arg, void* tag,
   PthreadCall("unlock", MutexUnlock(lock));
 }
 
-int ThreadPool::UnSchedule(void* arg) {
+int ThreadPoolImpl::UnSchedule(void* arg) {
   int count = 0;
 
   Lock lock(mu_);
@@ -374,4 +372,10 @@ int ThreadPool::UnSchedule(void* arg) {
   return count;
 }
 
+ThreadPool* NewThreadPool(int num_threads) {
+  ThreadPoolImpl* thread_pool = new ThreadPoolImpl();
+  thread_pool->SetBackgroundThreads(num_threads);
+  return thread_pool;
+}
+
 }  // namespace rocksdb

util/threadpool_imp.h

@@ -13,6 +13,7 @@
 #endif
 
 #include "rocksdb/env.h"
+#include "rocksdb/threadpool.h"
 #include "util/thread_status_util.h"
 
 #ifdef ROCKSDB_STD_THREADPOOL
@@ -26,23 +27,23 @@
 
 namespace rocksdb {
 
-class ThreadPool {
+class ThreadPoolImpl : public ThreadPool {
  public:
-  ThreadPool();
+  ThreadPoolImpl();
-  ~ThreadPool();
+  ~ThreadPoolImpl();
 
-  void JoinAllThreads();
+  void JoinAllThreads() override;
   void LowerIOPriority();
   void BGThread(size_t thread_id);
   void WakeUpAllThreads();
   void IncBackgroundThreadsIfNeeded(int num);
-  void SetBackgroundThreads(int num);
+  void SetBackgroundThreads(int num) override;
   void StartBGThreads();
   void Schedule(void (*function)(void* arg1), void* arg, void* tag,
                 void (*unschedFunction)(void* arg));
   int UnSchedule(void* arg);
 
-  unsigned int GetQueueLen() const {
+  unsigned int GetQueueLen() const override {
     return queue_len_.load(std::memory_order_relaxed);
   }