我是C++初学者，最近开始学习并发编程。我目前正在尝试使用多线程扫描系统磁盘并构建包含所有文件路径的Trie树。但是，我在测试过程中遇到了问题。
在我的 main.cpp 中，当循环索引 i 为 2、4 或 6 时，程序可以正确运行。但是，当 i 为 8 或 10（有时 i = 8 有效）时，程序会崩溃，并在以下位置出现访问冲突错误：行 if (m_tasks.empty()) 返回 false;在 WorkStealQueue::pop 函数中，显示消息“访问冲突读取位置 0x00000014”。
我尝试了各种方法来解决这个问题，但都没有成功。我非常感谢社区为解决此问题提供的任何帮助或指导。
提前非常感谢您！
下面是详细的代码实现（我的操作平台是Windows。）：
// workstealthreadpool.h
#pragma once
#include <deque>
#include <functional>
#include <mutex>
#include <thread>
#include <future>
#include <vector>
class WorkStealQueue
{
public:
WorkStealQueue() = default;
WorkStealQueue(const WorkStealQueue& rhs) = delete;
WorkStealQueue& operator=(const WorkStealQueue& rhs) = delete;
~WorkStealQueue() = default;
void push(std::function<void()> task);
bool pop(std::function<void()>& task);
bool steal(std::function<void()>& task);
private:
std::deque<std::function<void()>> m_tasks;
std::mutex m_mutex;
};
class WorkStealThreadPool
{
public:
explicit WorkStealThreadPool(std::size_t threadNums)
: m_stop(false) { init(threadNums); }
~WorkStealThreadPool();
template<typename Callback, typename... Args>
auto addTask(Callback&& func, Args&&... args)->std::future<typename std::result_of<Callback(Args...)>::type>;
private:
void init(std::size_t threadNums);
bool stealTask(std::function<void()>& task);
void worker(size_t index);
private:
std::vector<std::thread> m_workThreads;
std::vector<std::unique_ptr<WorkStealQueue>> m_taskQueues;
std::atomic<bool> m_stop;
static thread_local std::size_t m_index;
};
template<typename Callback, typename... Args>
auto WorkStealThreadPool::addTask(Callback&& func, Args&&... args) -> std::future<typename std::result_of<Callback(Args...)>::type>
{
using returnType = typename std::result_of<Callback(Args...)>::type;
auto task = std::make_shared<std::packaged_task<returnType()>>(std::bind(std::forward<Callback>(func), std::forward<Args>(args)...));
std::future<returnType> result = task->get_future();
{
m_taskQueues[m_index]->push([task]() { (*task)(); });
}
return result;
}
// workstealthreadpool.cpp
#include "workstealthreadpool.h"
void WorkStealQueue::push(std::function<void()> task)
{
std::lock_guard<std::mutex> lock(m_mutex);
m_tasks.emplace_back(std::move(task));
}
bool WorkStealQueue::pop(std::function<void()>& task)
{
std::lock_guard<std::mutex> lock(m_mutex);
if (m_tasks.empty()) return false;
task = std::move(m_tasks.front());
m_tasks.pop_front();
return true;
}
bool WorkStealQueue::steal(std::function<void()>& task)
{
std::lock_guard<std::mutex> lock(m_mutex);
if (m_tasks.empty()) return false;
task = std::move(m_tasks.back());
m_tasks.pop_back();
return true;
}
thread_local std::size_t WorkStealThreadPool::m_index;
void WorkStealThreadPool::init(std::size_t threadNums)
{
for (std::size_t i = 0; i < threadNums; ++i)
{
m_taskQueues.emplace_back(std::make_unique<WorkStealQueue>());
m_workThreads.emplace_back(&WorkStealThreadPool::worker, this, i);
}
}
WorkStealThreadPool::~WorkStealThreadPool()
{
m_stop = true;
for (std::thread& workerThread : m_workThreads)
{
if (workerThread.joinable())
{
workerThread.join();
}
}
}
bool WorkStealThreadPool::stealTask(std::function<void()>& task)
{
for (std::size_t i = 0; i < m_taskQueues.size(); ++i)
{
std::size_t index = (m_index + i + 1) % m_taskQueues.size();
if (m_taskQueues[index]->steal(task))
{
return true;
}
}
return false;
}
void WorkStealThreadPool::worker(std::size_t index)
{
m_index = index;
while (!m_stop)
{
std::function<void()> task;
if (m_taskQueues[m_index]->pop(task) || stealTask(task))
{
task();
}
else
{
std::this_thread::yield();
}
}
}
// scanner.h
#pragma once
#include "workstealthreadpool.h"
#include <QMap>
#include <QString>
struct TrieNode
{
QMap<TrieNode*, QString> childs;
TrieNode* parent = nullptr;
};
class Scanner
{
public:
explicit Scanner(std::size_t threadNums);
virtual ~Scanner();
virtual void scanDrives(const QStringList& drives);
virtual bool isScanCompleted();
virtual std::vector<TrieNode*> fetchScanResults();
private:
void scanCore(const QString& currentPath, TrieNode* parent);
void clearTrie(TrieNode* root);
private:
TrieNode* m_root;
WorkStealThreadPool* m_threadPool;
std::mutex m_mutex;
std::vector<TrieNode*> m_fileNodes;
std::atomic<int> m_taskCount;
};
#ifdef _DEBUG
void Print(TrieNode* root);
void Print(std::vector<TrieNode*>* fileNodes);
#endif
// scanner.cpp
#include "scanner.h"
#include <QDir>
Scanner::Scanner(std::size_t threadNums)
: m_root(nullptr)
, m_threadPool(nullptr)
, m_taskCount(0)
{
if (threadNums != 0)
{
m_threadPool = new WorkStealThreadPool(threadNums);
}
}
Scanner::~Scanner()
{
delete m_threadPool;
clearTrie(m_root);
}
void Scanner::scanDrives(const QStringList& drives)
{
clearTrie(m_root);
m_fileNodes.clear();
m_root = new TrieNode();
for (const QString& drive : drives)
{
TrieNode* child = new TrieNode();
child->parent = m_root;
m_root->childs[child] = drive;
scanCore(drive, child);
}
}
bool Scanner::isScanCompleted()
{
return m_taskCount.load(std::memory_order_acquire) == 0;
}
std::vector<TrieNode*> Scanner::fetchScanResults()
{
if (!isScanCompleted())
{
std::lock_guard<std::mutex> lock(m_mutex);
return m_fileNodes;
}
return m_fileNodes;
}
void Scanner::scanCore(const QString& currentPath, TrieNode* parent)
{
QDir dir(currentPath);
if (!dir.exists()) return;
QStringList fileNames = dir.entryList(QDir::Files);
for (const QString& fileName : fileNames)
{
TrieNode* child = new TrieNode();
child->parent = parent;
parent->childs[child] = fileName;
std::lock_guard<std::mutex> lock(m_mutex);
m_fileNodes.emplace_back(child);
}
QStringList subdirNames = dir.entryList(QDir::Dirs | QDir::NoDotAndDotDot);
for (const QString& subdirName : subdirNames)
{
QString childPath = currentPath + QDir::separator() + subdirName;
TrieNode* child = new TrieNode();
child->parent = parent;
parent->childs[child] = subdirName + "/";
if (m_threadPool)
{
m_taskCount.fetch_add(1, std::memory_order_release);
m_threadPool->addTask([this, childPath, child]
{
scanCore(childPath, child);
m_taskCount.fetch_sub(1, std::memory_order_acquire);
}
);
}
else {
scanCore(childPath, child);
}
}
}
void Scanner::clearTrie(TrieNode* root)
{
if (root == nullptr || root->childs.empty()) return;
for (auto iter = root->childs.begin(); iter != root->childs.end(); ++iter)
{
clearTrie(iter.key());
}
delete root;
}
#ifdef _DEBUG
void Print(TrieNode* root)
{
static int level = 0;
if (root == nullptr || root->childs.empty()) return;
for (auto iter = root->childs.begin(); iter != root->childs.end(); ++iter)
{
qDebug().noquote() << QString(" ").repeated(level) << iter.value();
++level;
Print(iter.key());
--level;
}
}
#endif
#ifdef _DEBUG
void Print(std::vector<TrieNode*>* fileNodes)
{
for (TrieNode* fileNode : *fileNodes)
{
qDebug().noquote() << fileNode->parent->childs[fileNode];
}
}
#endif
//main.cpp
#include "scanner.h"
#include <QStorageInfo>
#include <chrono>
void TestScanDrives(Scanner& scanner, const QStringList& drives)
{
scanner.scanDrives(drives);
while (!scanner.isScanCompleted())
{
std::this_thread::sleep_for(std::chrono::seconds(1));
}
}
int main()
{
QStringList drives;
for (const QStorageInfo& drive : QStorageInfo::mountedVolumes())
{
if (drive.isValid() && drive.isReady())
{
drives << drive.rootPath();
}
}
for (int i = 2; i <= 10; i += 2)
{
Scanner scanner(i);
TestScanDrives(scanner, drives);
}
return 0;
}
我仔细检查了 WorkStealQueue 类的实现，特别是 pop 和 push 方法，以确保它们正确处理任务。我将原子变量 m_taskCount 的内存顺序调整为不同的值，看看它是否会影响问题。我尝试改进 WorkStealThreadPool 中的线程同步和任务终止逻辑，但没有看到明显的改进。
您对
m_taskQueues.size()for (std::size_t i = 0; i < threadNums; ++i)
{
m_taskQueues.emplace_back(std::make_unique<WorkStealQueue>());
m_workThreads.emplace_back(&WorkStealThreadPool::worker, this, i);
}
当一个工作进程产生时，它可以尝试从它之后的线程中窃取工作，该线程尚未构造，因此将此循环分成两个。
for (std::size_t i = 0; i < threadNums; ++i)
{
m_taskQueues.emplace_back(std::make_unique<WorkStealQueue>());
}
for (std::size_t i = 0; i < threadNums; ++i)
{
m_workThreads.emplace_back(&WorkStealThreadPool::worker, this, i);
}