C pthread互斥: Expected expression before `{'

Question

我正在使用 pthread 库创建两个线程。我正在使用两个队列在两个线程(生产者-消费者)之间传递数据，因此希望有一个互斥锁来同步线程队列中的 push-pops。

但是我得到如下编译错误:

$ gcc simple-tun.c simple-tun -lpthread
simple-tun.c: In function ‘new_queue’:
simple-tun.c:920:13: error: expected expression before ‘{’ token

我得到错误的函数是:

908 struct queue * new_queue () {
909 
910     struct queue * q;
911     q = (struct queue *) malloc (sizeof(struct queue));
912 
913     if (q == NULL)
914         return NULL;
915 
916 
917     q->head = NULL;
918     q->tail = NULL;
919     q->is_empty = 1;
920     q->mutex = PTHREAD_MUTEX_INITIALIZER;
921 
922     return q;
923 }

结构队列是:

    struct queue {
 80     struct node * head;
 81     struct node * tail;
 82     int is_empty;
 83     pthread_mutex_t mutex;
 84 };

如果我注释掉第 920 行，链接器开始给出“多个声明错误”

$ gcc simple-tun.c simple-tun -lpthread
simple-tun: In function `settun':
(.text+0x2b7): multiple definition of `settun'
/tmp/cc5Ms4xP.o:simple-tun.c:(.text+0x1cb): first defined here
simple-tun: In function `_fini':
(.fini+0x0): multiple definition of `_fini'
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crti.o:(.fini+0x0): first defined here
simple-tun: In function `mktun':
(.text+0x1e2): multiple definition of `mktun'
/tmp/cc5Ms4xP.o:simple-tun.c:(.text+0xf6): first defined here
simple-tun: In function `net_connect':
(.text+0xe27): multiple definition of `net_connect'
/tmp/cc5Ms4xP.o:simple-tun.c:(.text+0x1115): first defined here
simple-tun: In function `data_start':
(.data+0x0): multiple definition of `__data_start'
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crt1.o:(.data+0x0): first defined here
simple-tun: In function `client_connect':
(.text+0xe95): multiple definition of `client_connect'
/tmp/cc5Ms4xP.o:simple-tun.c:(.text+0x1183): first defined here
simple-tun: In function `data_start':
(.data+0x8): multiple definition of `__dso_handle'
/usr/lib/gcc/x86_64-linux-gnu/4.7/crtbegin.o:(.data+0x0): first defined here
simple-tun:(.rodata+0x0): multiple definition of `_IO_stdin_used'
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crt1.o:(.rodata.cst4+0x0): first defined here
simple-tun: In function `server_connect':
(.text+0xfa2): multiple definition of `server_connect'
/tmp/cc5Ms4xP.o:simple-tun.c:(.text+0x1290): first defined here
simple-tun: In function `print_usage':
(.text+0xe05): multiple definition of `print_usage'
/tmp/cc5Ms4xP.o:simple-tun.c:(.text+0x10f3): first defined here
simple-tun: In function `_init':
(.init+0x0): multiple definition of `_init'
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crti.o:(.init+0x0): first defined here
/usr/lib/gcc/x86_64-linux-gnu/4.7/crtend.o:(.tm_clone_table+0x0): multiple definition of `__TMC_END__'
simple-tun:(.data+0x10): first defined here
/usr/bin/ld: error in simple-tun(.eh_frame); no .eh_frame_hdr table will be created.
collect2: error: ld returned 1 exit status

我无法在搜索中找到解决方案。我的代码有什么根本性的错误吗？有人可以帮助我发现我做错了什么吗？

如果我需要发布更多片段或更多输出，请告诉我。

Answer 1

1. 您不能像那样使用 PTHREAD_MUTEX_INITIALIZER - 它必须用作初始值设定项，而不是在正则赋值表达式中。您有两种选择来修复它 - 调用 pthread_mutex_init()，或添加类型转换以将 PTHREAD_MUTEX_INITIALIZER 用作复合文字。您的选择:

   pthread_mutex_init(&q->mutex, NULL);
   

   或:

   q->mutex = (pthread_mutex_t)PTHREAD_MUTEX_INITIALIZER;
   

2. 您的链接器错误问题是由以下命令行引起的:

   gcc simple-tun.c simple-tun -lpthread
   

   您缺少 -o，因此您试图将程序与其自身链接。这是个坏消息。您可能想要的是:

   gcc simple-tun.c -o simple-tun -lpthread
   

   实际上，您也应该在其中添加一些警告标志。