使用pthread时，字节仍可访问

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所以我按照无用的建议再次更新代码，以便您可以看到可以编译和运行的内容。我从其他东西清理了一些代码，但问题仍然存在。当我给出SIGINT信号时，用valgrind执行它，程序通过正确打印终止的线程结束，但有时它结束时没有内存泄漏，其他人报告了一些内存泄漏我忘在脑后。目前我正在进行没有连接客户端的测试。

我正在尝试创建一个多线程服务器，它使用select（）函数和一个大学项目的线程池。用Valgrind执行我的代码我发现在发送SIGINT信号后，有时它会终止而没有错误，而有时它会报告4个“仍然可达”的错误。

我用valgrind启动程序，指定以下标志：

 valgrind --leak-check=full --show-leak-kinds=all

这是新代码

#define _POSIX_C_SOURCE 200809L
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>
#include <signal.h>
#include <pthread.h>

#include <errno.h>
#include <sys/select.h>
#include <ctype.h>
#include <sys/types.h> 
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/time.h>

#define UNIXPATH "./tmp/socket"
#define THREADSINPOOL 8
#define MAXCONNECTION 32
#define SYSCALL(r,c,msg) 
    if((r=c)==-1) {perror(msg); exit(errno); }


typedef struct _elem{
    long connfd;
    struct _elem *next;
}elem;

static volatile sig_atomic_t terminate=0;

int try=0;
int nelem=0;
elem *head=NULL;
elem *corr=NULL;
elem *tmp=NULL;


pthread_mutex_t mtx=PTHREAD_MUTEX_INITIALIZER;  
pthread_cond_t empty=PTHREAD_COND_INITIALIZER;
pthread_cond_t full=PTHREAD_COND_INITIALIZER;

int update(fd_set set, int fdmax){
    for(int i=(fdmax-1);i>=0; i--)
        if(FD_ISSET(i,&set)) return i;
    return -1;
}

void *threadF(void *arg){
    pthread_t self;
    long connfd=0;

    while(1){
        pthread_mutex_lock(&mtx);
        if(try==1){
            pthread_mutex_unlock(&mtx);
            break;
        } 
        while(nelem==0 && try==0)
            pthread_cond_wait(&empty,&mtx);
        if(try==1){ 
            pthread_mutex_unlock(&mtx);
            break;
        }
        nelem--;

        tmp=head;
        connfd=tmp->connfd;
        tmp=tmp->next;
        free(head); 
        head=tmp;

        pthread_cond_signal(&full);
        pthread_mutex_unlock(&mtx);

        //read & write on tmp->connfd

        self = pthread_self();
        printf("tmp->connfd: %lu on thread: %lu
", connfd,self);
        close(connfd);
    }
    pthread_exit(0);        
}

void insert(long connfd){
    pthread_mutex_lock(&mtx);
    while(nelem==MAXCONNECTION && try==0)
        pthread_cond_wait(&full,&mtx);
    if(try==1){ 
        pthread_mutex_unlock(&mtx);

    }else{
        nelem++;
        elem *new=malloc(sizeof(elem));
        new->connfd=connfd;
        new->next=NULL;
        if(head==NULL){
            head=new;
            corr=head;
        }else{
            corr->next=new;
            corr=corr->next;
        }
        pthread_cond_signal(&empty);
        pthread_mutex_unlock(&mtx);
    }
}

pthread_t *createarray(pthread_t *array){
    int i,err;
    pthread_t id;
    for(i=0;i<THREADSINPOOL;i++){
        if((err=pthread_create(&id,NULL,&threadF,NULL))!=0){
            fprintf(stderr,"thread
");
            exit(errno);
        }
        array[i]=id;
    }
    return array;

}

void destroyArray(pthread_t *array){
    void* value=NULL;
    int i,tmp;
    for (i = 0; i < THREADSINPOOL; i++){
        if ((tmp=pthread_join(array[i],&value)) != 0)
                printf("error join: %d
", tmp);
        printf("thread: %lu terminated
",array[i]);
    }
    free(array);
}

void cleanup(){
    unlink(UNIXPATH);
}

void sigint_handler(int signmum){
    terminate=1;

}

int main(int argc, char *argv[]) {
    cleanup();
    atexit(cleanup);
    int notused;

    sigset_t setmask;
    SYSCALL(notused,sigemptyset(&setmask),"SIGEMPTYSET");
    SYSCALL(notused,sigaddset(&setmask,SIGINT),"SIGADDSET");
    SYSCALL(notused,pthread_sigmask(SIG_SETMASK,&setmask,NULL),"pthread_sigmask");

    //create threadspool
    pthread_t *array=malloc(THREADSINPOOL*sizeof(pthread_t));
    array=createarray(array);

    struct sigaction s;
    memset(&s,0,sizeof(s));

    s.sa_handler=sigint_handler;
    s.sa_flags=SA_RESTART;
    SYSCALL(notused,sigaction(SIGINT,&s,NULL),"SIGINT");

    SYSCALL(notused,sigemptyset(&setmask),"SIGEMPTYSET");
    SYSCALL(notused,pthread_sigmask(SIG_SETMASK,&setmask,NULL),"sigmask");


    int listenfd;
    SYSCALL(listenfd, socket(AF_UNIX, SOCK_STREAM, 0), "socket");

    struct sockaddr_un serv_addr;
    memset(&serv_addr, '0', sizeof(serv_addr));
    serv_addr.sun_family = AF_UNIX;
    strncpy(serv_addr.sun_path, UNIXPATH, strlen(UNIXPATH)+1);

    SYSCALL(notused, bind(listenfd, (struct sockaddr*)&serv_addr,sizeof(serv_addr)), "bind"); 
    SYSCALL(notused, listen(listenfd, MAXCONNECTION), "listen");

    long fd_c;
    int i=0; 

    fd_set set, rdset;

    FD_ZERO(&rdset);
    FD_ZERO (&set); 
    FD_SET(listenfd,&set); 

    int fd_num=listenfd; 

    struct timeval tv;
    tv.tv_sec=3;
    tv.tv_usec=0;

    while(1){
        if(terminate==1){
            break;
        }
        rdset=set; 
        if((notused=select(fd_num+1, &rdset, NULL, NULL, &tv))==-1){
            if(errno==EINTR){
                if(terminate==1){
                    break;
                }else{
                    perror("select");
                    exit(EXIT_FAILURE);
                }

            }

        }

        for(i=0; i<=fd_num;i++){
            if(FD_ISSET(i,&rdset)){
                if(i==listenfd){
                    SYSCALL(fd_c, accept(listenfd, (struct sockaddr*)NULL ,NULL), "accept");
                    printf("connection accepted
");
                    FD_SET(fd_c, &set);
                    if(fd_c>fd_num) fd_num=fd_c;
                }else{
                    fd_c=i;
                }
                insert(fd_c);
                FD_CLR(fd_c,&set);
                if(fd_c==fd_num) fd_num=update(set,fd_num);

            }
        }
    }
    pthread_mutex_lock(&mtx);
    try=1;
    pthread_mutex_unlock(&mtx);
    close(listenfd);
    pthread_cond_broadcast(&empty);
    pthread_cond_signal(&full);
    // join on the thread and free(array)
    destroyArray(array);
    if(tmp)
        free(tmp);
    return 0;
}

最后，这是我执行代码时有时得到的Valgrind输出：

==7578== Memcheck, a memory error detector
==7578== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==7578== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==7578== Command: ./server
==7578== 
^Cthread: 100800256 terminated
thread: 109192960 terminated
thread: 117585664 terminated
thread: 125978368 terminated
thread: 134371072 terminated
thread: 142763776 terminated
thread: 151156480 terminated
thread: 159549184 terminated
==7578== 
==7578== HEAP SUMMARY:
==7578==     in use at exit: 1,638 bytes in 4 blocks
==7578==   total heap usage: 15 allocs, 11 frees, 4,958 bytes allocated
==7578== 
==7578== 36 bytes in 1 blocks are still reachable in loss record 1 of 4
==7578==    at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7578==    by 0x401CF99: strdup (strdup.c:42)
==7578==    by 0x40187DE: _dl_load_cache_lookup (dl-cache.c:311)
==7578==    by 0x4009168: _dl_map_object (dl-load.c:2364)
==7578==    by 0x4015576: dl_open_worker (dl-open.c:237)
==7578==    by 0x4010563: _dl_catch_error (dl-error.c:187)
==7578==    by 0x4014DA8: _dl_open (dl-open.c:660)
==7578==    by 0x519A5AC: do_dlopen (dl-libc.c:87)
==7578==    by 0x4010563: _dl_catch_error (dl-error.c:187)
==7578==    by 0x519A663: dlerror_run (dl-libc.c:46)
==7578==    by 0x519A663: __libc_dlopen_mode (dl-libc.c:163)
==7578==    by 0x4E4B91A: pthread_cancel_init (unwind-forcedunwind.c:52)
==7578==    by 0x4E4BB03: _Unwind_ForcedUnwind (unwind-forcedunwind.c:126)
==7578== 
==7578== 36 bytes in 1 blocks are still reachable in loss record 2 of 4
==7578==    at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7578==    by 0x400BEF3: _dl_new_object (dl-object.c:165)
==7578==    by 0x400650C: _dl_map_object_from_fd (dl-load.c:1028)
==7578==    by 0x4008C26: _dl_map_object (dl-load.c:2498)
==7578==    by 0x4015576: dl_open_worker (dl-open.c:237)
==7578==    by 0x4010563: _dl_catch_error (dl-error.c:187)
==7578==    by 0x4014DA8: _dl_open (dl-open.c:660)
==7578==    by 0x519A5AC: do_dlopen (dl-libc.c:87)
==7578==    by 0x4010563: _dl_catch_error (dl-error.c:187)
==7578==    by 0x519A663: dlerror_run (dl-libc.c:46)
==7578==    by 0x519A663: __libc_dlopen_mode (dl-libc.c:163)
==7578==    by 0x4E4B91A: pthread_cancel_init (unwind-forcedunwind.c:52)
==7578==    by 0x4E4BB03: _Unwind_ForcedUnwind (unwind-forcedunwind.c:126)
==7578== 
==7578== 384 bytes in 1 blocks are still reachable in loss record 3 of 4
==7578==    at 0x4C2FB55: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7578==    by 0x40120BD: _dl_check_map_versions (dl-version.c:293)
==7578==    by 0x4015B18: dl_open_worker (dl-open.c:286)
==7578==    by 0x4010563: _dl_catch_error (dl-error.c:187)
==7578==    by 0x4014DA8: _dl_open (dl-open.c:660)
==7578==    by 0x519A5AC: do_dlopen (dl-libc.c:87)
==7578==    by 0x4010563: _dl_catch_error (dl-error.c:187)
==7578==    by 0x519A663: dlerror_run (dl-libc.c:46)
==7578==    by 0x519A663: __libc_dlopen_mode (dl-libc.c:163)
==7578==    by 0x4E4B91A: pthread_cancel_init (unwind-forcedunwind.c:52)
==7578==    by 0x4E4BB03: _Unwind_ForcedUnwind (unwind-forcedunwind.c:126)
==7578==    by 0x4E4A06F: __pthread_unwind (unwind.c:121)
==7578==    by 0x4E42844: __do_cancel (pthreadP.h:283)
==7578==    by 0x4E42844: pthread_exit (pthread_exit.c:28)
==7578== 
==7578== 1,182 bytes in 1 blocks are still reachable in loss record 4 of 4
==7578==    at 0x4C2FB55: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7578==    by 0x400BBF5: _dl_new_object (dl-object.c:75)
==7578==    by 0x400650C: _dl_map_object_from_fd (dl-load.c:1028)
==7578==    by 0x4008C26: _dl_map_object (dl-load.c:2498)
==7578==    by 0x4015576: dl_open_worker (dl-open.c:237)
==7578==    by 0x4010563: _dl_catch_error (dl-error.c:187)
==7578==    by 0x4014DA8: _dl_open (dl-open.c:660)
==7578==    by 0x519A5AC: do_dlopen (dl-libc.c:87)
==7578==    by 0x4010563: _dl_catch_error (dl-error.c:187)
==7578==    by 0x519A663: dlerror_run (dl-libc.c:46)
==7578==    by 0x519A663: __libc_dlopen_mode (dl-libc.c:163)
==7578==    by 0x4E4B91A: pthread_cancel_init (unwind-forcedunwind.c:52)
==7578==    by 0x4E4BB03: _Unwind_ForcedUnwind (unwind-forcedunwind.c:126)
==7578== 
==7578== LEAK SUMMARY:
==7578==    definitely lost: 0 bytes in 0 blocks
==7578==    indirectly lost: 0 bytes in 0 blocks
==7578==      possibly lost: 0 bytes in 0 blocks
==7578==    still reachable: 1,638 bytes in 4 blocks
==7578==         suppressed: 0 bytes in 0 blocks
==7578== 
==7578== For counts of detected and suppressed errors, rerun with: -v
==7578== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

新的Valgrind输出

==3920== Memcheck, a memory error detector
==3920== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==3920== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==3920== Command: ./server
==3920== 
^C
==3920== 
==3920== Process terminating with default action of signal 2 (SIGINT)
==3920==    at 0x4E3FE6D: __pthread_initialize_minimal (nptl-init.c:433)
==3920==    by 0x4E3F588: ??? (in /lib/x86_64-linux-gnu/libpthread-2.23.so)
==3920==    by 0x400044F: ??? (in /lib/x86_64-linux-gnu/ld-2.23.so)
==3920==    by 0x4010679: call_init.part.0 (dl-init.c:58)
==3920==    by 0x4010834: call_init (dl-init.c:104)
==3920==    by 0x4010834: _dl_init (dl-init.c:87)
==3920==    by 0x4000C69: ??? (in /lib/x86_64-linux-gnu/ld-2.23.so)
==3920== 
==3920== HEAP SUMMARY:
==3920==     in use at exit: 0 bytes in 0 blocks
==3920==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==3920== 
==3920== All heap blocks were freed -- no leaks are possible
==3920== 
==3920== For counts of detected and suppressed errors, rerun with: -v
==3920== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
答案

但有时它会在没有内存泄漏的情况下结束，其他人会报告我留下的一些内存泄漏。

这可能是因为程序在终止之前没有清理其已接受连接的链表。

但是您的代码中还有其他一些令人不安的问题。

  • 首先，您使用terminate变量不是线程安全的。不要被sig_atomic_t类型的名称混淆：it is not an atomic datatype。信号处理程序使用它可以安全地与接收信号的线程进行通信，但是在不使用适当的同步对象（例如互斥锁）的情况下在线程之间进行通信是不安全的。此外，尽管需要与信号处理程序一起使用，making it volatile also fails to confer thread safety。这是您当前代码的问题，因为当您发送SIGINT时，它可以由任何线程处理。 我建议通过阻止SIGINT除了主线程之外的所有解决方案。当进程收到一个进程指示的信号时，它会排队等待当时没有被阻塞的线程，所以你不必担心成功接收信号。每个线程都有自己的信号掩码，其初始值是从其父线程继承的。因此，我建议在启动所有工作程序之前在主线程中阻塞SIGINT，然后在工作程序全部运行后仅在主线程中解除阻塞。
  • 其次，对线程之间共享的可变非原子数据的所有访问都需要由适当的同步对象保护。您已为此选择了一个互斥锁，但您的程序在没有其保护的情况下执行某些访问。 共享数据至少包括变量try，nelem以及由head领导的链表的所有内容。 threadF()在不持有互斥锁的情况下检查try main()没有持有互斥锁就设置了try 因此，程序的行为是不确定的。在实践中，这似乎不太可能与“泄漏”有关，但它可能会导致您的程序偶尔无法完全关闭。原则上，任何事情都可能发生。在实践中，最可能的影响是您的程序偶尔无法干净地关闭。

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