esballoc(9F) Example

Example 8-5 (which will not compile) shows how extended buffers are managed in the multithreaded environment. The driver maintains a pool of special memory that is allocated by esballoc(9F). The allocator free routine uses the queue struct assigned to the driver or other queue private data, so the allocator and the close routine need to coordinate to ensure that no outstanding esballoc(9F) memory blocks remain after the close. The special memory blocks are of type ebm_t, the counter is ebm, the mutex mp and the condition variable cvp are used to implement the coordination.

Example 8-5 esballoc Example

ebm_t *
special_new()
{
		mutex_enter(&mp);
		/*
 	 * allocate some special memory
		 */
		esballoc();
		/*
		 * increment counter
		 */
		ebm++;
		mutex_exit(&mp);
}

void
special_free()
{
		mutex_enter(&mp);
		/*
 	 * de-allocate some special memory
		 */
		freeb();
	
		/*
		 * decrement counter
		 */
		ebm--;
		if (ebm == 0)
			cv_broadcast(&cvp);
		mutex_exit(&mp);
}

open_close(q, .....)
	....
{
		/*
		 * do some stuff
		 */
		/*
		 * Time to decommission the special allocator.  Are there
		 * any outstanding allocations from it?
		 */
		mutex_enter(&mp);
		while (ebm > 0)
			cv_wait(&cvp, &mp);
	
		mutex_exit(&mp);
}

Close routine must wait for all esballoc(9F) memory to be freed.