这是用两个线程初始化信号量的正确方法

Question

我是使用信号量概念的新手。我想要做的是将一个发送者和一个接收者集成到一个项目中，这样如果我运行这个项目，发送者和接收者就可以同时交换数据。下面是我尝试过但我的Eclipse CDT IDE显示
**error: ‘receiver’ undeclared (first use in this function) pthread_create(mythread2, NULL, (void*)receiver, NULL);**

任何帮助赞赏。

sem_t semaphore; 

void sender() { 
    while (1) { 
     sem_wait(& semaphore); 
     printf("Hello from the sender!\n"); 
     sleep(1); /* do not run so fast! */ 
     /* Write any number of messages, re-using the existing string-buffer: no leak!!. */ 
     for (i = 1; i <= NUM_MSG; i++) { 
      msg - > index = i; 
      snprintf(msg - > content, MAX_MSG_LEN, "Message no. %d", msg - > index); 
      printf("Writing message: %s\n", msg - > content); 
      status = Chat_ChatMessageDataWriter_write(talker, msg, userHandle); 
      checkStatus(status, "Chat_ChatMessageDataWriter_write"); 
      sleep(1); /* do not run so fast! */ 
     } 
     sem_post(& semaphore); 
     printf("hello before exit\n"); 
     //  pthread_exit(NULL); 
     printf("hello after exit\n"); 
     sleep(1); 
    } 
    void receiver() { 
     while (0) { 
      sem_wait(& semaphore); 
      printf("Hello from the receiver!\n"); 
      while (!terminated) { 

       status = Chat_ChatMessageDataReader_take(
        chatAdmin, 
        msgSeq, 
        infoSeq, 
        DDS_LENGTH_UNLIMITED, 
        DDS_ANY_SAMPLE_STATE, 
        DDS_ANY_VIEW_STATE, 
        DDS_ALIVE_INSTANCE_STATE); 

       checkStatus(status, "Chat_NamedMessageDataReader_take"); 

       for (i = 0; i < msgSeq - > _length; i++) { 
        Chat_ChatMessage * msg = & (msgSeq - > _buffer[i]); 
        printf("%s\n", msg - > content); 
        fflush(stdout); 
       } 
      } 
      sem_post(& semaphore); 

      status = Chat_ChatMessageDataReader_return_loan(chatAdmin, msgSeq, infoSeq); 
      checkStatus(status, "Chat_ChatMessageDataReader_return_loan"); 

      /* Sleep for some amount of time, as not to consume too much CPU cycles. */ 
#ifdef USE_NANOSLEEP 
      sleeptime.tv_sec = 0; 
      sleeptime.tv_nsec = 100000000; 
      nanosleep(& sleeptime, & remtime); 
#elif defined _WIN32 
      Sleep(100); 
#else 
      usleep(1000000); 
#endif 
     } 
    } 
} 

int main(void) { 
    -- -- -- -- -- -- -- -- -- -- -- -- 
    -- -- -- -- -- -- -- -- -- -- -- -- 
    -- -- -- -- -- -- -- -- -- -- -- -- 

    /* Use the changed policy when defining the ChatMessage topic */ 
    chatMessageTopic = DDS_DomainParticipant_create_topic(
     participant, 
     "Chat_ChatMessage", 
     chatMessageTypeName, 
     history_topic_qos, 
     NULL, 
     DDS_STATUS_MASK_NONE); 
    checkHandle(chatMessageTopic, "DDS_DomainParticipant_create_topic (ChatMessage)"); 

    /* Create a Publisher for the chatter application. */ 
    chatPublisher = DDS_DomainParticipant_create_publisher(participant, pub_qos, NULL, DDS_STATUS_MASK_NONE); 
    checkHandle(chatPublisher, "DDS_DomainParticipant_create_publisher"); 

    /* Create a DataWriter for the ChatMessage Topic (using the appropriate QoS). */ 
    talker = DDS_Publisher_create_datawriter(
     chatPublisher, 
     chatMessageTopic, 
     DDS_DATAWRITER_QOS_USE_TOPIC_QOS, 
     NULL, 
     DDS_STATUS_MASK_NONE); 
    checkHandle(talker, "DDS_Publisher_create_datawriter (chatMessage)"); 

    /* Initialize the chat messages on Heap. */ 
    msg = Chat_ChatMessage__alloc(); 
    checkHandle(msg, "Chat_ChatMessage__alloc"); 
    msg - > userID = ownID; 
    msg - > index = 0; 
    msg - > content = DDS_string_alloc(MAX_MSG_LEN); 
    checkHandle(msg - > content, "DDS_string_alloc"); 

    snprintf(msg - > content, MAX_MSG_LEN, "Hi there, I will send you %d more messages.", NUM_MSG); 

    printf("Writing message: %s\n", msg - > content); 

    /* Register a chat message for this user (pre-allocating resources for it!!) */ 
    userHandle = DDS__FooDataWriter_register_instance(talker, msg); 

    /* Write a message using the pre-generated instance handle. */ 
    status = DDS__FooDataWriter_write(talker, msg, userHandle); 
    checkStatus(status, "Chat_ChatMessageDataWriter_write"); 
    /* Create a Subscriber for the MessageBoard application. */ 
    chatSubscriber = DDS_DomainParticipant_create_subscriber(participant, sub_qos, NULL, DDS_STATUS_MASK_NONE); 
    checkHandle(chatSubscriber, "DDS_DomainParticipant_create_subscriber"); 
    /* Create a DataReader for the chatMessageTopic Topic (using the appropriate QoS). */ 
    chatAdmin = DDS_Subscriber_create_datareader(
     chatSubscriber, 
     chatMessageTopic, 
     DDS_DATAREADER_QOS_USE_TOPIC_QOS, 
     NULL, 
     DDS_STATUS_MASK_NONE); 
    checkHandle(chatAdmin, "DDS_Subscriber_create_datareader"); 

    /* Print a message that the MessageBoard has opened. */ 
    printf("MessageBoard has opened: send ChatMessages \n\n"); 

    /* Allocate the sequence holders for the DataReader */ 
    msgSeq = DDS_sequence_Chat_ChatMessage__alloc(); 
    checkHandle(msgSeq, "DDS_sequence_Chat_NamedMessage__alloc"); 
    infoSeq = DDS_SampleInfoSeq__alloc(); 
    checkHandle(infoSeq, "DDS_SampleInfoSeq__alloc"); 

    //initializing the semaphore 
    sem_init(& semaphore, 0, 1); 
    pthread_t * mythread1; 
    pthread_t * mythread2; 
    mythread1 = (pthread_t *) malloc(sizeof(* mythread1)); 
    mythread2 = (pthread_t *) malloc(sizeof(* mythread2)); 
    //start the thread 
    printf("Starting thread, semaphore is unlocked.\n"); 
    pthread_create(mythread1, NULL, (void *) sender, NULL); 
    pthread_create(mythread2, NULL, (void *) receiver, NULL); 
    getchar(); 
    sem_wait(& semaphore); 
    printf("Semaphore locked.\n"); 
    getchar(); 
    printf("Semaphore Unlocked.\n"); 
    sem_post(& semaphore); 
    getchar(); 
    return 0; 
} 

Answer 1

看起来你在函数'sender'的末尾缺少一个右括号'}'。这应该解决您的具体错误“'未经申报'的接收方”。

[此外， “而（0）{...}” 构建功能 '接收器' 是值得商榷...]

虽然我回答，请允许我建议如下：

1）锁定/同步（在本例中为信号量）的问题与DDS（或任何其他数据通信机制）正交。 [你可能会有更多的成功，如果你可以保持代码清洁和专注于在这样的论坛上寻求帮助]

2）DDS的一些实现（我只能说专门为CoreDX DDS） - 安全，因此不需要围绕API调用提供保护。 [您可能想要与特定的DDS供应商进行确认。]从这个例子中，我很难推断您的应用程序逻辑是否需要锁定，但似乎没有。