Multiple clients calling a server IPC

1

Is this safe? I have a server that writes to a file and I want multiple apps to be able to call the server to write new files. If they call while the last function is still executing while this be a problem or is the state saved?

for example
void FileManager_StoreFile(const char* writeData)
{
FILE* fp = fopen(filename,“w+”);
//<— Another client calls api
//write to file etc
}

will write Data be lost if another client calls the function before it is written? if so how can I fix this?

2

did you try to use semaphore API to lock this critical section?

3

No Sorry I’m not super familiar with thread concepts but that’s what I was looking for I think thank you

4

Actually I don’t think that will work it says for threads in the same process theres not really a way for me to get a reference to the semaphore from outside of the executable?

5

did you write a sample code to try that?

6

Hi @sast5.

You really only need the reference to the semaphore within the executable providing the API.

Basically, you could create a semaphore in the COMPONENT_INIT section with an initial count of 1 then use that reference in your API function(s).

For example:

COMPONENT_INIT
{
  /*
   * Create a semaphore with an initial count of 1 
   * This signals that 1 resource (a single file) is available
   */
}

void FileManager_StoreFile(const char* writeData)
{
  /*
   * Pend (wait) on the semaphore using either:
   * le_sem_WaitWithTimeOut()
   * le_sem_Wait()
   * le_sem_TryWait()
   * Note: the first client calling the API will `consume` the semaphore
   */
   
   // If le_sem above returned LE_OK, it is safe to `use` the resource.

   FILE* fp = fopen(filename,“w+”);

   // ... do stuff with the file, etc.

   /* 
    * *** <— Another client calls api ***
    * Other clients won't be able to acquire the resource until 
    * the `consuming` client releases (posts) it.
    * The behavior will depend on which `waiting` method you chose to implement.
    */

   // Finally, Post the semaphore so other clients may `use` it.
   le_sem_Post(MySemRef);
}

Raf

7

Oh ok thanks makes more sense with an example (Couldn’t see any other posts about semaphores on the forums/Doc samples)