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我正在使用 C++11 std::thread。它的主循环包括一个阻塞的 recvfrom() 调用，它侦听到达 DATAGRAM 套接字的 UDP 数据包，以及一些解析消息并在进程中操作 STL 容器负载的复杂代码。

线程属于一个类（helloexchange），由构造函数启动，应该在析构函数中取消。出于显而易见的原因，我不想强​​行终止线程，因为这可能会破坏部分位于类之外的数据结构。

当使用pthread代替时std::thread，有一种pthread_cancel方法，它与 结合使用pthread_setcancelstate，提供了我需要的所有功能：它只会在线程在某些系统调用中阻塞时取消线程，并且可以在某些部分完全禁用取消。一旦再次启用，就会执行取消。这是工作pthread代码的完整示例：

#include <arpa/inet.h>
#include <unistd.h>
#include <iostream>
#include <sys/socket.h>
#include <sys/types.h>
#include <cstdio>
#include <pthread.h>
#include <net/if.h>
#include <ifaddrs.h>

int sock;

void *tfun(void *arg) {
    std::cout << "Thread running" << std::endl;
    while(true) {
        char buf[256];
        struct sockaddr_in addr;
        addr.sin_family = AF_INET;
        socklen_t addrlen = sizeof(addr);
        //allow cancelling the thread
        pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);

        //perform the blocking recvfrom syscall
        int size = recvfrom(sock, (void *) buf, sizeof(buf), 0,
            (struct sockaddr *) &addr, &addrlen);

        //disallow cancelling the thread
        pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, NULL);

        if(size < 0) {
            perror("Could not receive packet");
            return NULL;
        } else {
            //process the packet in the most complex ways
            //you could imagine.
            std::cout << "Packet received: " << size << " bytes";
            std::cout << std::endl;
        }
    }
    return NULL;
}


int main() {
    //open datagram socket
    sock = socket(AF_INET, SOCK_DGRAM, 0);
    if(sock < 0) {
        perror("Could not open socket");
        return 1;
    }
    //bind socket to port
    struct sockaddr_in addr;
    addr.sin_family = AF_INET;
    addr.sin_port = htons(1337);
    addr.sin_addr.s_addr = 0;
    if(bind(sock, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
        perror("Could not bind datagram socket");
        return 2;
    }
    //create the listener thread
    pthread_t t;
    if(pthread_create(&t, NULL, tfun, NULL) != 0) {
        perror("Could not thread");
        return 3;
    };
    //wait
    std::cin.get();
    //cancel the listener thread. pthread_cancel does not block.
    std::cout << "Cancelling thread" << std::endl;
    if(pthread_cancel(t) != 0) {
        perror("Could not cancel thread");
    }
    //join (blocks until the thread has actually cancelled).
    std::cout << "Joining thread" << std::endl;
    if(pthread_join(t, NULL) != 0) {
        perror("Could not join thread");
    } else {
        std::cout << "Join successful" << std::endl;
    }
    //close socket
    if(close(sock) != 0) {
        perror("Could not close socket");
    };
}

但是，std::thread不支持cancel，也不std::this_thread支持setcancelstate（您会在此处找到参考）。但是，它确实支持native_handle，它返回内部使用的pthread_tid。但是，将 pthread_cancel() 发送到线程的本机句柄的明显方法会导致分段错误：

#include <iostream>
#include <thread>
#include <cstdio>

#include <arpa/inet.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <pthread.h>
#include <net/if.h>
#include <ifaddrs.h>

int sock;

void tfun() {
    std::cout << "Thread running" << std::endl;
    while(true) {
        char buf[256];
        struct sockaddr_in addr;
        addr.sin_family = AF_INET;
        socklen_t addrlen = sizeof(addr);

        //perform the blocking recvfrom syscall
        int size = recvfrom(sock, (void *) buf, sizeof(buf), 0,
            (struct sockaddr *) &addr, &addrlen);

        if(size < 0) {
            perror("Could not receive packet");
            return;
        } else {
            //process the packet in the most complex ways
            //you could imagine.
            std::cout << "Packet received: " << size << " bytes";
            std::cout << std::endl;
        }
    }
    return;
}

int main() {
    //open datagram socket
    sock = socket(AF_INET, SOCK_DGRAM, 0);
    if(sock < 0) {
        perror("Could not open socket");
        return 1;
    }
    //bind socket to port
    struct sockaddr_in addr;
    addr.sin_family = AF_INET;
    addr.sin_port = htons(1337);
    addr.sin_addr.s_addr = 0;
    if(bind(sock, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
        perror("Could not bind datagram socket");
        return 2;
    }
    //the listener thread
    std::thread *t = new std::thread(&tfun);
    //wait
    std::cin.get();
    //cancel the listener thread. pthread_cancel does not block.
    std::cout << "Cancelling thread" << std::endl;
    if(pthread_cancel(t->native_handle()) != 0) {
        perror("Could not cancel thread");
    }
    //join (blocks until the thread has actually cancelled).
    std::cout << "Joining thread" << std::endl;
    t->join();
    delete t;
    //close socket
    if(close(sock) != 0) {
        perror("Could not close socket");
    };
}

结果是：

(gdb) run
Starting program: /tmp/test/test-dbg 
warning: Could not load shared library symbols for linux-vdso.so.1.
Do you need "set solib-search-path" or "set sysroot"?
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
[New Thread 0x7ffff6550700 (LWP 11329)]
Thread running

Cancelling thread
Joining thread

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff6550700 (LWP 11329)]
0x00007ffff6e67b45 in __gnu_cxx::__verbose_terminate_handler() () from /usr/lib/libstdc++.so.6

有没有办法取消std::thread它在系统调用中阻塞的时间？

编辑

我不是要跨平台解决方案；符合 POSIX 的解决方案就足够了。

4

2 回答 2

4

我将建议一种解决方法，类似于众所周知的自管道技巧，以解除阻塞select(2)并回避整个混乱的线程取消业务。

由于您知道socket(7)线程阻塞的 IP 地址和端口，因此只有sendto(2)一些从主线程发送到它的知名哨兵数据包，这表明是时候跳出循环了。

这样您就不必颠覆std::thread抽象并且可以保持合理的可移植性。

编辑0：

如果您不喜欢解决方法，请将其称为技术:)

于 2012-09-09T16:25:15.267 回答
3

您可以通过向线程发送信号（例如，SIGUSR1）来中断recvfrom。在 linux 上，您必须禁用 libc 自动重启行为（有关详细信息，请参阅recv() 不会被多线程环境中的信号中断）才能正常工作。

于 2012-09-10T14:02:59.720 回答