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rocksdb/util/threadpool_imp.cc

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root 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.
#include "util/threadpool_imp.h"
#ifndef OS_WIN
#include <unistd.h>
#endif
#ifdef OS_LINUX
#include <sys/resource.h>
#include <sys/syscall.h>
#endif
#include <stdlib.h>
#include <algorithm>
#include <atomic>
#include <condition_variable>
refactor SavePoints (#5192) Summary: Savepoints are assumed to be used in a stack-wise fashion (only the top element should be used), so they were stored by `WriteBatch` in a member variable `save_points` using an std::stack. Conceptually this is fine, but the implementation had a few issues: - the `save_points_` instance variable was a plain pointer to a heap- allocated `SavePoints` struct. The destructor of `WriteBatch` simply deletes this pointer. However, the copy constructor of WriteBatch just copied that pointer, meaning that copying a WriteBatch with active savepoints will very likely have crashed before. Now a proper copy of the savepoints is made in the copy constructor, and not just a copy of the pointer - `save_points_` was an std::stack, which defaults to `std::deque` for the underlying container. A deque is a bit over the top here, as we only need access to the most recent savepoint (i.e. stack.top()) but never any elements at the front. std::deque is rather expensive to initialize in common environments. For example, the STL implementation shipped with GNU g++ will perform a heap allocation of more than 500 bytes to create an empty deque object. Although the `save_points_` container is created lazily by RocksDB, moving from a deque to a plain `std::vector` is much more memory-efficient. So `save_points_` is now a vector. - `save_points_` was changed from a plain pointer to an `std::unique_ptr`, making ownership more explicit. Pull Request resolved: https://github.com/facebook/rocksdb/pull/5192 Differential Revision: D15024074 Pulled By: maysamyabandeh fbshipit-source-id: 5b128786d3789cde94e46465c9e91badd07a25d7
6 years ago
#include <deque>
#include <mutex>
#include <sstream>
#include <thread>
#include <vector>
#include "monitoring/thread_status_util.h"
#include "port/port.h"
#include "test_util/sync_point.h"
#include "util/string_util.h"
namespace ROCKSDB_NAMESPACE {
void ThreadPoolImpl::PthreadCall(const char* label, int result) {
if (result != 0) {
fprintf(stderr, "pthread %s: %s\n", label, errnoStr(result).c_str());
abort();
}
}
struct ThreadPoolImpl::Impl {
Impl();
~Impl();
void JoinThreads(bool wait_for_jobs_to_complete);
void SetBackgroundThreadsInternal(int num, bool allow_reduce);
int GetBackgroundThreads();
unsigned int GetQueueLen() const {
return queue_len_.load(std::memory_order_relaxed);
}
void LowerIOPriority();
void LowerCPUPriority(CpuPriority pri);
void WakeUpAllThreads() { bgsignal_.notify_all(); }
void BGThread(size_t thread_id);
void StartBGThreads();
void Submit(std::function<void()>&& schedule,
std::function<void()>&& unschedule, void* tag);
int UnSchedule(void* arg);
void SetHostEnv(Env* env) { env_ = env; }
Env* GetHostEnv() const { return env_; }
bool HasExcessiveThread() const {
return static_cast<int>(bgthreads_.size()) > total_threads_limit_;
}
// Return true iff the current thread is the excessive thread to terminate.
// Always terminate the running thread that is added last, even if there are
// more than one thread to terminate.
bool IsLastExcessiveThread(size_t thread_id) const {
return HasExcessiveThread() && thread_id == bgthreads_.size() - 1;
}
bool IsExcessiveThread(size_t thread_id) const {
return static_cast<int>(thread_id) >= total_threads_limit_;
}
// Return the thread priority.
// This would allow its member-thread to know its priority.
Env::Priority GetThreadPriority() const { return priority_; }
// Set the thread priority.
void SetThreadPriority(Env::Priority priority) { priority_ = priority; }
int ReserveThreads(int threads_to_be_reserved) {
std::unique_lock<std::mutex> lock(mu_);
// We can reserve at most num_waiting_threads_ in total so the number of
// threads that can be reserved might be fewer than the desired one. In
// rare cases, num_waiting_threads_ could be less than reserved_threads
// due to SetBackgroundThreadInternal or last excessive threads. If that
// happens, we cannot reserve any other threads.
int reserved_threads_in_success =
std::min(std::max(num_waiting_threads_ - reserved_threads_, 0),
threads_to_be_reserved);
reserved_threads_ += reserved_threads_in_success;
return reserved_threads_in_success;
}
int ReleaseThreads(int threads_to_be_released) {
std::unique_lock<std::mutex> lock(mu_);
// We cannot release more than reserved_threads_
int released_threads_in_success =
std::min(reserved_threads_, threads_to_be_released);
reserved_threads_ -= released_threads_in_success;
WakeUpAllThreads();
return released_threads_in_success;
}
private:
static void BGThreadWrapper(void* arg);
bool low_io_priority_;
CpuPriority cpu_priority_;
Env::Priority priority_;
Env* env_;
int total_threads_limit_;
std::atomic_uint queue_len_; // Queue length. Used for stats reporting
// Number of reserved threads, managed by ReserveThreads(..) and
// ReleaseThreads(..), if num_waiting_threads_ is no larger than
// reserved_threads_, its thread will be blocked to ensure the reservation
// mechanism
int reserved_threads_;
// Number of waiting threads (Maximum number of threads that can be
// reserved), in rare cases, num_waiting_threads_ could be less than
// reserved_threads due to SetBackgroundThreadInternal or last
// excessive threads.
int num_waiting_threads_;
bool exit_all_threads_;
bool wait_for_jobs_to_complete_;
// Entry per Schedule()/Submit() call
struct BGItem {
void* tag = nullptr;
std::function<void()> function;
std::function<void()> unschedFunction;
};
using BGQueue = std::deque<BGItem>;
BGQueue queue_;
std::mutex mu_;
std::condition_variable bgsignal_;
std::vector<port::Thread> bgthreads_;
};
inline ThreadPoolImpl::Impl::Impl()
: low_io_priority_(false),
cpu_priority_(CpuPriority::kNormal),
priority_(Env::LOW),
env_(nullptr),
Introduce bottom-pri thread pool for large universal compactions Summary: When we had a single thread pool for compactions, a thread could be busy for a long time (minutes) executing a compaction involving the bottom level. In multi-instance setups, the entire thread pool could be consumed by such bottom-level compactions. Then, top-level compactions (e.g., a few L0 files) would be blocked for a long time ("head-of-line blocking"). Such top-level compactions are critical to prevent compaction stalls as they can quickly reduce number of L0 files / sorted runs. This diff introduces a bottom-priority queue for universal compactions including the bottom level. This alleviates the head-of-line blocking situation for fast, top-level compactions. - Added `Env::Priority::BOTTOM` thread pool. This feature is only enabled if user explicitly configures it to have a positive number of threads. - Changed `ThreadPoolImpl`'s default thread limit from one to zero. This change is invisible to users as we call `IncBackgroundThreadsIfNeeded` on the low-pri/high-pri pools during `DB::Open` with values of at least one. It is necessary, though, for bottom-pri to start with zero threads so the feature is disabled by default. - Separated `ManualCompaction` into two parts in `PrepickedCompaction`. `PrepickedCompaction` is used for any compaction that's picked outside of its execution thread, either manual or automatic. - Forward universal compactions involving last level to the bottom pool (worker thread's entry point is `BGWorkBottomCompaction`). - Track `bg_bottom_compaction_scheduled_` so we can wait for bottom-level compactions to finish. We don't count them against the background jobs limits. So users of this feature will get an extra compaction for free. Closes https://github.com/facebook/rocksdb/pull/2580 Differential Revision: D5422916 Pulled By: ajkr fbshipit-source-id: a74bd11f1ea4933df3739b16808bb21fcd512333
7 years ago
total_threads_limit_(0),
queue_len_(),
reserved_threads_(0),
num_waiting_threads_(0),
exit_all_threads_(false),
wait_for_jobs_to_complete_(false),
queue_(),
mu_(),
bgsignal_(),
bgthreads_() {}
inline ThreadPoolImpl::Impl::~Impl() { assert(bgthreads_.size() == 0U); }
void ThreadPoolImpl::Impl::JoinThreads(bool wait_for_jobs_to_complete) {
std::unique_lock<std::mutex> lock(mu_);
assert(!exit_all_threads_);
wait_for_jobs_to_complete_ = wait_for_jobs_to_complete;
exit_all_threads_ = true;
// prevent threads from being recreated right after they're joined, in case
// the user is concurrently submitting jobs.
total_threads_limit_ = 0;
reserved_threads_ = 0;
num_waiting_threads_ = 0;
lock.unlock();
bgsignal_.notify_all();
for (auto& th : bgthreads_) {
th.join();
}
bgthreads_.clear();
exit_all_threads_ = false;
wait_for_jobs_to_complete_ = false;
}
inline void ThreadPoolImpl::Impl::LowerIOPriority() {
std::lock_guard<std::mutex> lock(mu_);
low_io_priority_ = true;
}
inline void ThreadPoolImpl::Impl::LowerCPUPriority(CpuPriority pri) {
std::lock_guard<std::mutex> lock(mu_);
cpu_priority_ = pri;
}
void ThreadPoolImpl::Impl::BGThread(size_t thread_id) {
bool low_io_priority = false;
CpuPriority current_cpu_priority = CpuPriority::kNormal;
while (true) {
// Wait until there is an item that is ready to run
std::unique_lock<std::mutex> lock(mu_);
// Stop waiting if the thread needs to do work or needs to terminate.
// Increase num_waiting_threads_ once this task has started waiting
num_waiting_threads_++;
TEST_SYNC_POINT("ThreadPoolImpl::BGThread::WaitingThreadsInc");
TEST_IDX_SYNC_POINT("ThreadPoolImpl::BGThread::Start:th", thread_id);
// When not exist_all_threads and the current thread id is not the last
// excessive thread, it may be blocked due to 3 reasons: 1) queue is empty
// 2) it is the excessive thread (not the last one)
// 3) the number of waiting threads is not greater than reserved threads
// (i.e, no available threads due to full reservation")
while (!exit_all_threads_ && !IsLastExcessiveThread(thread_id) &&
(queue_.empty() || IsExcessiveThread(thread_id) ||
num_waiting_threads_ <= reserved_threads_)) {
bgsignal_.wait(lock);
}
// Decrease num_waiting_threads_ once the thread is not waiting
num_waiting_threads_--;
if (exit_all_threads_) { // mechanism to let BG threads exit safely
if (!wait_for_jobs_to_complete_ || queue_.empty()) {
break;
}
} else if (IsLastExcessiveThread(thread_id)) {
// Current thread is the last generated one and is excessive.
// We always terminate excessive thread in the reverse order of
// generation time. But not when `exit_all_threads_ == true`,
// otherwise `JoinThreads()` could try to `join()` a `detach()`ed
// thread.
auto& terminating_thread = bgthreads_.back();
terminating_thread.detach();
bgthreads_.pop_back();
if (HasExcessiveThread()) {
// There is still at least more excessive thread to terminate.
WakeUpAllThreads();
}
TEST_IDX_SYNC_POINT("ThreadPoolImpl::BGThread::Termination:th",
thread_id);
TEST_SYNC_POINT("ThreadPoolImpl::BGThread::Termination");
break;
}
auto func = std::move(queue_.front().function);
queue_.pop_front();
queue_len_.store(static_cast<unsigned int>(queue_.size()),
std::memory_order_relaxed);
bool decrease_io_priority = (low_io_priority != low_io_priority_);
CpuPriority cpu_priority = cpu_priority_;
lock.unlock();
if (cpu_priority < current_cpu_priority) {
TEST_SYNC_POINT_CALLBACK("ThreadPoolImpl::BGThread::BeforeSetCpuPriority",
&current_cpu_priority);
// 0 means current thread.
port::SetCpuPriority(0, cpu_priority);
current_cpu_priority = cpu_priority;
TEST_SYNC_POINT_CALLBACK("ThreadPoolImpl::BGThread::AfterSetCpuPriority",
&current_cpu_priority);
}
#ifdef OS_LINUX
if (decrease_io_priority) {
#define IOPRIO_CLASS_SHIFT (13)
#define IOPRIO_PRIO_VALUE(class, data) (((class) << IOPRIO_CLASS_SHIFT) | data)
// Put schedule into IOPRIO_CLASS_IDLE class (lowest)
// These system calls only have an effect when used in conjunction
// with an I/O scheduler that supports I/O priorities. As at
// kernel 2.6.17 the only such scheduler is the Completely
// Fair Queuing (CFQ) I/O scheduler.
// To change scheduler:
// echo cfq > /sys/block/<device_name>/queue/schedule
// Tunables to consider:
// /sys/block/<device_name>/queue/slice_idle
// /sys/block/<device_name>/queue/slice_sync
syscall(SYS_ioprio_set, 1, // IOPRIO_WHO_PROCESS
0, // current thread
IOPRIO_PRIO_VALUE(3, 0));
low_io_priority = true;
}
#else
(void)decrease_io_priority; // avoid 'unused variable' error
#endif
TEST_SYNC_POINT_CALLBACK("ThreadPoolImpl::Impl::BGThread:BeforeRun",
&priority_);
func();
}
}
// Helper struct for passing arguments when creating threads.
struct BGThreadMetadata {
ThreadPoolImpl::Impl* thread_pool_;
size_t thread_id_; // Thread count in the thread.
BGThreadMetadata(ThreadPoolImpl::Impl* thread_pool, size_t thread_id)
: thread_pool_(thread_pool), thread_id_(thread_id) {}
};
void ThreadPoolImpl::Impl::BGThreadWrapper(void* arg) {
BGThreadMetadata* meta = reinterpret_cast<BGThreadMetadata*>(arg);
size_t thread_id = meta->thread_id_;
ThreadPoolImpl::Impl* tp = meta->thread_pool_;
#ifdef ROCKSDB_USING_THREAD_STATUS
// initialize it because compiler isn't good enough to see we don't use it
// uninitialized
ThreadStatus::ThreadType thread_type = ThreadStatus::NUM_THREAD_TYPES;
switch (tp->GetThreadPriority()) {
case Env::Priority::HIGH:
thread_type = ThreadStatus::HIGH_PRIORITY;
break;
case Env::Priority::LOW:
thread_type = ThreadStatus::LOW_PRIORITY;
break;
case Env::Priority::BOTTOM:
thread_type = ThreadStatus::BOTTOM_PRIORITY;
break;
case Env::Priority::USER:
thread_type = ThreadStatus::USER;
break;
case Env::Priority::TOTAL:
assert(false);
return;
}
assert(thread_type != ThreadStatus::NUM_THREAD_TYPES);
ThreadStatusUtil::RegisterThread(tp->GetHostEnv(), thread_type);
#endif
delete meta;
tp->BGThread(thread_id);
#ifdef ROCKSDB_USING_THREAD_STATUS
ThreadStatusUtil::UnregisterThread();
#endif
return;
}
void ThreadPoolImpl::Impl::SetBackgroundThreadsInternal(int num,
bool allow_reduce) {
std::lock_guard<std::mutex> lock(mu_);
if (exit_all_threads_) {
return;
}
if (num > total_threads_limit_ ||
(num < total_threads_limit_ && allow_reduce)) {
total_threads_limit_ = std::max(0, num);
WakeUpAllThreads();
StartBGThreads();
}
}
int ThreadPoolImpl::Impl::GetBackgroundThreads() {
std::unique_lock<std::mutex> lock(mu_);
return total_threads_limit_;
}
void ThreadPoolImpl::Impl::StartBGThreads() {
// Start background thread if necessary
while ((int)bgthreads_.size() < total_threads_limit_) {
port::Thread p_t(&BGThreadWrapper,
new BGThreadMetadata(this, bgthreads_.size()));
// Set the thread name to aid debugging
#if defined(_GNU_SOURCE) && defined(__GLIBC_PREREQ)
#if __GLIBC_PREREQ(2, 12)
auto th_handle = p_t.native_handle();
std::string thread_priority = Env::PriorityToString(GetThreadPriority());
std::ostringstream thread_name_stream;
thread_name_stream << "rocksdb:";
for (char c : thread_priority) {
thread_name_stream << static_cast<char>(tolower(c));
}
pthread_setname_np(th_handle, thread_name_stream.str().c_str());
#endif
#endif
bgthreads_.push_back(std::move(p_t));
}
}
void ThreadPoolImpl::Impl::Submit(std::function<void()>&& schedule,
std::function<void()>&& unschedule,
void* tag) {
std::lock_guard<std::mutex> lock(mu_);
if (exit_all_threads_) {
return;
}
StartBGThreads();
// Add to priority queue
queue_.push_back(BGItem());
TEST_SYNC_POINT("ThreadPoolImpl::Submit::Enqueue");
auto& item = queue_.back();
item.tag = tag;
item.function = std::move(schedule);
item.unschedFunction = std::move(unschedule);
queue_len_.store(static_cast<unsigned int>(queue_.size()),
std::memory_order_relaxed);
if (!HasExcessiveThread()) {
// Wake up at least one waiting thread.
bgsignal_.notify_one();
} else {
// Need to wake up all threads to make sure the one woken
// up is not the one to terminate.
WakeUpAllThreads();
}
}
int ThreadPoolImpl::Impl::UnSchedule(void* arg) {
int count = 0;
std::vector<std::function<void()>> candidates;
{
std::lock_guard<std::mutex> lock(mu_);
// Remove from priority queue
BGQueue::iterator it = queue_.begin();
while (it != queue_.end()) {
if (arg == (*it).tag) {
if (it->unschedFunction) {
candidates.push_back(std::move(it->unschedFunction));
}
it = queue_.erase(it);
count++;
} else {
++it;
}
}
queue_len_.store(static_cast<unsigned int>(queue_.size()),
std::memory_order_relaxed);
}
// Run unschedule functions outside the mutex
for (auto& f : candidates) {
f();
}
return count;
}
ThreadPoolImpl::ThreadPoolImpl() : impl_(new Impl()) {}
ThreadPoolImpl::~ThreadPoolImpl() {}
void ThreadPoolImpl::JoinAllThreads() { impl_->JoinThreads(false); }
void ThreadPoolImpl::SetBackgroundThreads(int num) {
impl_->SetBackgroundThreadsInternal(num, true);
}
int ThreadPoolImpl::GetBackgroundThreads() {
return impl_->GetBackgroundThreads();
}
unsigned int ThreadPoolImpl::GetQueueLen() const {
return impl_->GetQueueLen();
}
void ThreadPoolImpl::WaitForJobsAndJoinAllThreads() {
impl_->JoinThreads(true);
}
void ThreadPoolImpl::LowerIOPriority() { impl_->LowerIOPriority(); }
void ThreadPoolImpl::LowerCPUPriority(CpuPriority pri) {
impl_->LowerCPUPriority(pri);
}
void ThreadPoolImpl::IncBackgroundThreadsIfNeeded(int num) {
impl_->SetBackgroundThreadsInternal(num, false);
}
void ThreadPoolImpl::SubmitJob(const std::function<void()>& job) {
auto copy(job);
impl_->Submit(std::move(copy), std::function<void()>(), nullptr);
}
void ThreadPoolImpl::SubmitJob(std::function<void()>&& job) {
impl_->Submit(std::move(job), std::function<void()>(), nullptr);
}
void ThreadPoolImpl::Schedule(void (*function)(void* arg1), void* arg,
void* tag, void (*unschedFunction)(void* arg)) {
if (unschedFunction == nullptr) {
impl_->Submit(std::bind(function, arg), std::function<void()>(), tag);
} else {
impl_->Submit(std::bind(function, arg), std::bind(unschedFunction, arg),
tag);
}
}
int ThreadPoolImpl::UnSchedule(void* arg) { return impl_->UnSchedule(arg); }
void ThreadPoolImpl::SetHostEnv(Env* env) { impl_->SetHostEnv(env); }
Env* ThreadPoolImpl::GetHostEnv() const { return impl_->GetHostEnv(); }
// Return the thread priority.
// This would allow its member-thread to know its priority.
Env::Priority ThreadPoolImpl::GetThreadPriority() const {
return impl_->GetThreadPriority();
}
// Set the thread priority.
void ThreadPoolImpl::SetThreadPriority(Env::Priority priority) {
impl_->SetThreadPriority(priority);
}
// Reserve a specific number of threads, prevent them from running other
// functions The number of reserved threads could be fewer than the desired one
int ThreadPoolImpl::ReserveThreads(int threads_to_be_reserved) {
return impl_->ReserveThreads(threads_to_be_reserved);
}
// Release a specific number of threads
int ThreadPoolImpl::ReleaseThreads(int threads_to_be_released) {
return impl_->ReleaseThreads(threads_to_be_released);
}
ThreadPool* NewThreadPool(int num_threads) {
ThreadPoolImpl* thread_pool = new ThreadPoolImpl();
thread_pool->SetBackgroundThreads(num_threads);
return thread_pool;
}
} // namespace ROCKSDB_NAMESPACE