From 1a992bf023f386f8973ead747abe4f9726bf0a55 Mon Sep 17 00:00:00 2001
From: Silent <zdanio95@gmail.com>
Date: Sat, 10 Aug 2019 20:25:16 +0200
Subject: [PATCH] Store std::thread in worker thread class by value and
 explicitly start it up, and don't use shared_ptr in thread pools

---
 ext/native/thread/threadpool.cpp | 21 +++++++++++----------
 ext/native/thread/threadpool.h   | 12 ++++++------
 2 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/ext/native/thread/threadpool.cpp b/ext/native/thread/threadpool.cpp
index d48fd6a994..cdf98fd1de 100644
--- a/ext/native/thread/threadpool.cpp
+++ b/ext/native/thread/threadpool.cpp
@@ -1,20 +1,23 @@
 #include "base/logging.h"
 #include "thread/threadpool.h"
 #include "thread/threadutil.h"
+#include "Common/MakeUnique.h"
 
 ///////////////////////////// WorkerThread
 
-WorkerThread::WorkerThread() {
-	thread.reset(new std::thread(std::bind(&WorkerThread::WorkFunc, this)));
-}
-
 WorkerThread::~WorkerThread() {
 	{
 		std::lock_guard<std::mutex> guard(mutex);
 		active = false;
 		signal.notify_one();
 	}
-	thread->join();
+	if (thread.joinable()) {
+		thread.join();
+	}
+}
+
+void WorkerThread::StartUp() {
+	thread = std::thread(std::bind(&WorkerThread::WorkFunc, this));
 }
 
 void WorkerThread::Process(std::function<void()> work) {
@@ -50,10 +53,6 @@ void WorkerThread::WorkFunc() {
 	}
 }
 
-LoopWorkerThread::LoopWorkerThread() : WorkerThread(true) {
-	thread.reset(new std::thread(std::bind(&LoopWorkerThread::WorkFunc, this)));
-}
-
 void LoopWorkerThread::Process(std::function<void(int, int)> work, int start, int end) {
 	std::lock_guard<std::mutex> guard(mutex);
 	work_ = std::move(work);
@@ -99,7 +98,9 @@ ThreadPool::ThreadPool(int numThreads) {
 void ThreadPool::StartWorkers() {
 	if (!workersStarted) {
 		for(int i = 0; i < numThreads_; ++i) {
-			workers.push_back(std::make_shared<LoopWorkerThread>());
+			auto workerPtr = make_unique<LoopWorkerThread>();
+			workerPtr->StartUp();
+			workers.push_back(std::move(workerPtr));
 		}
 		workersStarted = true;
 	}
diff --git a/ext/native/thread/threadpool.h b/ext/native/thread/threadpool.h
index 581302d7d2..2064b31c28 100644
--- a/ext/native/thread/threadpool.h
+++ b/ext/native/thread/threadpool.h
@@ -12,18 +12,18 @@
 // Only handles a single item of work at a time.
 class WorkerThread {
 public:
-	WorkerThread();
+	WorkerThread() = default;
 	virtual ~WorkerThread();
 
+	void StartUp();
+
 	// submit a new work item
 	void Process(std::function<void()> work);
 	// wait for a submitted work item to be completed
 	void WaitForCompletion();
 
 protected:
-	WorkerThread(bool ignored) {}
-
-	std::unique_ptr<std::thread> thread; // the worker thread
+	std::thread thread; // the worker thread
 	std::condition_variable signal; // used to signal new work
 	std::condition_variable done; // used to signal work completion
 	std::mutex mutex, doneMutex; // associated with each respective condition variable
@@ -41,7 +41,7 @@ private:
 
 class LoopWorkerThread final : public WorkerThread {
 public:
-	LoopWorkerThread();
+	LoopWorkerThread() = default;
 	void Process(std::function<void(int, int)> work, int start, int end);
 
 private:
@@ -65,7 +65,7 @@ public:
 
 private:
 	int numThreads_;
-	std::vector<std::shared_ptr<LoopWorkerThread>> workers;
+	std::vector<std::unique_ptr<LoopWorkerThread>> workers;
 	std::mutex mutex; // used to sequentialize loop execution
 
 	bool workersStarted = false;