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Commit 48dc17ef authored by Sharvil Nanavati's avatar Sharvil Nanavati
Browse files

Expose semaphore's file descriptor. 

|semaphore_get_fd| can be used by callers to determine if it's safe
to call |semaphore_wait| and |semaphore_post| without blocking.

Change-Id: Icf758f03ea2aa85cddcb4ab3f7906b2c587fb8ac
parent 933e4d6e

system/osi/include/semaphore.h

+12 −0
Original line number Diff line number Diff line
@@ -43,3 +43,15 @@ bool semaphore_try_wait(semaphore_t *semaphore); 


// Increments the value of |semaphore|. |semaphore| may not be NULL.

void semaphore_post(semaphore_t *semaphore);



// Returns a file descriptor representing this semaphore. The caller may

// only perform one operation on the file descriptor: select(2). If |select|

// indicates the fd is readable, the caller may call |semaphore_wait|

// without blocking. If select indicates the fd is writable, the caller may

// call |semaphore_post| without blocking. Note that there may be a race

// condition between calling |select| and |semaphore_wait| or |semaphore_post|

// which results in blocking behaviour.

//

// The caller must not close the returned file descriptor. |semaphore| may not

// be NULL.

int semaphore_get_fd(const semaphore_t *semaphore);

system/osi/src/semaphore.c

+6 −0
Original line number Diff line number Diff line
@@ -93,3 +93,9 @@ void semaphore_post(semaphore_t *semaphore) { 
  if (eventfd_write(semaphore->fd, 1ULL) == -1)

    ALOGE("%s unable to post to semaphore: %s", __func__, strerror(errno));

}



int semaphore_get_fd(const semaphore_t *semaphore) {

  assert(semaphore != NULL);

  assert(semaphore->fd != -1);

  return semaphore->fd;

}