mic*_*c_e 8 c++ linux pthreads c++11
我正在使用C++ 11 std :: thread.它的主循环包括一个阻塞的recvfrom()调用,它监听到达DATAGRAM套接字的UDP数据包,以及一些复杂的代码,用于解析消息并在进程中处理大量的STL容器.
该线程属于一个class(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,因为这可能会破坏数据结构,这些数据结构部分位于类之外.
当使用pthread而不是时std::thread,有一种pthread_cancel方法,它与pthread_setcancelstate我一起提供了我需要的所有功能:它只会在某些系统调用中阻塞时取消线程,并且对于某些部分可以完全禁用取消.一旦再次启用取消,则执行取消.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(你会在这里找到一个参考).但它确实支持native_handle,它返回内部使用的pthread_tid.然而,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
有没有办法取消一段std::thread时间它在系统调用中阻塞？
编辑
我不是要求跨平台的解决方案; 符合POSIX的解决方案就足够了.