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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include "thread.h"
#include "threadexecutor.h"
#include "eventbarrier.hpp"
#include "arrayqueue.hpp"
#include "gate.h"
#include "executor_idle_tracking.h"
#include <vector>
#include <functional>
namespace vespalib {
/**
* An executor service that executes tasks in multiple threads.
**/
class ThreadStackExecutorBase : public SyncableThreadExecutor,
public Runnable
{
public:
using unique_lock = std::unique_lock<std::mutex>;
private:
struct TaggedTask {
Task::UP task;
uint32_t token;
TaggedTask() : task(nullptr), token(0) {}
TaggedTask(Task::UP task_in, uint32_t token_in)
: task(std::move(task_in)), token(token_in) {}
TaggedTask(TaggedTask &&rhs) = default;
TaggedTask(const TaggedTask &rhs) = delete;
TaggedTask &operator=(const TaggedTask &rhs) = delete;
TaggedTask &operator=(TaggedTask &&rhs) {
assert(task.get() == nullptr); // no overwrites
task = std::move(rhs.task);
token = rhs.token;
return *this;
}
};
struct Worker {
std::mutex lock;
std::condition_variable cond;
ThreadIdleTracker idleTracker;
uint32_t pre_guard;
bool idle;
uint32_t post_guard;
TaggedTask task;
Worker();
void verify(bool expect_idle) const;
};
struct BarrierCompletion {
Gate gate;
void completeBarrier() { gate.countDown(); }
};
struct BlockedThread {
const uint32_t wait_task_count;
mutable std::mutex lock;
mutable std::condition_variable cond;
bool blocked;
BlockedThread(uint32_t wait_task_count_in)
: wait_task_count(wait_task_count_in), lock(), cond(), blocked(true) {}
void wait() const;
void unblock();
};
ThreadPool _pool;
mutable std::mutex _lock;
std::condition_variable _cond;
ExecutorStats _stats;
ExecutorIdleTracker _idleTracker;
Gate _executorCompletion;
ArrayQueue<TaggedTask> _tasks;
ArrayQueue<Worker*> _workers;
std::vector<BlockedThread*> _blocked;
EventBarrier<BarrierCompletion> _barrier;
uint32_t _taskCount;
uint32_t _taskLimit;
bool _closed;
init_fun_t _init_fun;
static thread_local ThreadStackExecutorBase *_master;
void block_thread(const unique_lock &, BlockedThread &blocked_thread);
void unblock_threads(const unique_lock &);
/**
* Assign the given task to the given idle worker. This will wake
* up a worker thread that is blocked in the obtainTask function.
*
* @param task the task to assign
* @param worker an idle worker
**/
void assignTask(TaggedTask task, Worker &worker);
/**
* Obtain a new task to be run by the given worker. This function
* will block until a task is obtained or the executor is shut
* down.
*
* @return true if a task was obtained, false if we are done
* @param worker the worker looking for work
**/
bool obtainTask(Worker &worker);
// Runnable (all workers live here)
void run() override;
protected:
/**
* This will tell if a task will be accepted or not.
* An implementation might decide to block.
*/
virtual bool acceptNewTask(unique_lock & guard, std::condition_variable & cond) = 0;
/**
* If blocking implementation, this might wake up any waiters.
*
* @param monitor to use for signaling.
*/
virtual void wakeup(unique_lock & guard, std::condition_variable & cond) = 0;
/**
* Will tell you if the executor has been closed for new tasks.
*/
bool closed() const { return _closed; }
/**
* This will cleanup before destruction. All implementations must call this
* in destructor.
*/
void cleanup();
/**
* Will tell if there is room for a new task in the Q.
*/
bool isRoomForNewTask() const { return (_taskCount < _taskLimit); }
/**
* Create a new thread stack executor. The task limit specifies
* the maximum number of tasks that are currently handled by this
* executor. Both the number of threads and the task limit must be
* greater than 0.
*
* @param taskLimit upper limit on accepted tasks
* @param init_fun custom function used to wrap the main loop of
* each worker thread.
**/
ThreadStackExecutorBase(uint32_t taskLimit, init_fun_t init_fun);
/**
* This will start the theads. This is to avoid starting tasks in
* constructor of base class.
*
* @param threads number of worker threads (concurrent tasks)
*/
void start(uint32_t threads);
/**
* Returns true if the current thread is owned by this executor.
**/
bool owns_this_thread() const { return (_master == this); }
/**
* Sets a new upper limit for accepted number of tasks.
*/
void internalSetTaskLimit(uint32_t taskLimit);
public:
ThreadStackExecutorBase(const ThreadStackExecutorBase &) = delete;
ThreadStackExecutorBase & operator = (const ThreadStackExecutorBase &) = delete;
/**
* Returns the number of idle workers. This is mostly useful for testing.
**/
size_t num_idle_workers() const;
ExecutorStats getStats() override;
Task::UP execute(Task::UP task) override;
/**
* Synchronize with this executor. This function will block until
* all previously accepted tasks have been executed. This function
* uses the event barrier algorithm (tm).
*
* @return this object; for chaining
**/
ThreadStackExecutorBase &sync() override;
/**
* Block the calling thread until the current task count is equal
* to or lower than the given value.
*
* @param task_count target value to wait for
**/
void wait_for_task_count(uint32_t task_count);
size_t getNumThreads() const override;
void setTaskLimit(uint32_t taskLimit) override;
uint32_t getTaskLimit() const override;
void wakeup() override;
/**
* Shut down this executor. This will make this executor reject
* all new tasks.
*
* @return this object; for chaining
**/
ThreadStackExecutorBase &shutdown() override;
/**
* Will invoke shutdown then sync.
**/
~ThreadStackExecutorBase() override;
};
} // namespace vespalib
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