這是用兩個線程初始化信號量的正確方法

Question

我是使用信號量概念的新手。我想要做的是將一個發送者和一個接收者集成到一個項目中，這樣如果我運行這個項目，發送者和接收者就可以同時交換數據。下面是我嘗試過但我的Eclipse CDT IDE顯示
**error: ‘receiver’ undeclared (first use in this function) pthread_create(mythread2, NULL, (void*)receiver, NULL);**

任何幫助讚賞。

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

看起來你在函數'sender'的末尾缺少一個右括號'}'。這應該解決您的具體錯誤「'未經申報'的接收方」。

[此外， 「而（0）{...}」 構建功能 '接收器' 是值得商榷...]

雖然我回答，請允許我建議如下：

1）鎖定/同步（在本例中爲信號量）的問題與DDS（或任何其他數據通信機制）正交。 [你可能會有更多的成功，如果你可以保持代碼清潔和專注於在這樣的論壇上尋求幫助]

2）DDS的一些實現（我只能說專門爲CoreDX DDS） - 安全，因此不需要圍繞API調用提供保護。 [您可能想要與特定的DDS供應商進行確認。]從這個例子中，我很難推斷您的應用程序邏輯是否需要鎖定，但似乎沒有。