将WIN32应用程序移植到Linux-事件在Linux中如何工作？

Question

I have a WIN32 application and I'm porting it to LINUX GNU. I have event base C code in WIN32 app. Now i have tried few methods to implement the same in GNU linux but somehow i'm getting feeling that this code will not work properly.

First of all, I created a structure to implement event.

typedef struct _Event
   {
      int m_bool;
      pthread_mutex_t m_mutex;
      pthread_cond_t m_condition;

   }MyEvent, * Event_handle;

To implement 'SetEvent' , 'ResetEvent', 'WaitForSingleObject', i have implemented following code.

   MyEvent CreateEvent( void )
   {
       MyEvent e1;
       e1.m_bool = 1;
       return e1;
   }

   void SetEvent( MyEvent evt )
   {
      evt.m_bool = 1;
      pthread_cond_broadcast(&evt.m_condition);
   }

   void ResetEvent( MyEvent evt )
   {
      evt.m_bool = 0;
      pthread_cond_broadcast(&evt.m_condition);
   }

   int WaitForSingleObject( MyEvent evt, unsigned timeout )
   {
         pthread_cond_wait(&(evt.m_condition),&(evt.m_mutex));
         return SUCCESS;
   }

Now m confused about the usage of m_mutex and m_bool. What i'm looking for is a sample code or demo.

I have tried all my keys to the lock but seems the door is still locked. Any help will do. Thanks !

Answer 1

It seems, I've found what you want. I'm not sure though. My first thought was you are not understanding why the mutex is here. I'll try explain it first.

On Windows©, when you call WaitForSingleObject() , it blocks the execution until you send a signal (or set an event in the signalled state, SetEvent() , in Windows terms). Basically, it's done by setting an implicit mutex inside the event object, locking it in the WaitForSingleObject() function and waiting for a signal.

In the POSIX world, you need to set up the mutex explicitly. One important notice: there's no ResetEvent -link behaviour—you don't need to reset your conditional variable; however, you need to unlock the mutex. Probably, the sole purpose of the ResetEvent() function is to unlock that implicit mutex.

void SetEvent(MyEvent evt)
{
    pthread_cond_signal(&evt.m_condition);
}

void ResetEvent(MyEvent evt)
{
    pthread_mutex_unlock(&evt.m_mutex);
}

int WaitForSingleObject(MyEvent evt, unsigned)
{
    pthread_mutex_lock(&evt.m_mutex);
    pthread_cond_wait(&evt.m_condition, &evt.m_mutex);
}

In you case, the pthread_cond_signal() is more appropriate. Also note that you need to use the pthread_cond_timedwait() function to mimic the WaitForSingleObject() function.

Further reading:

• man pthread_cond_wait
• man pthread_cond_signal