Initialize thread pool attributes

/* initialize thread pool attributes */
memset(&pool_attr, 0, sizeof pool_attr);
pool_attr.handle = dpp;
pool_attr.context_alloc = dispatch_context_alloc;
pool_attr.block_func = dispatch_block;
pool_attr.unblock_func = dispatch_unblock;
pool_attr.handler_func = dispatch_handler;
pool_attr.context_free = dispatch_context_free;
pool_attr.lo_water = 2;
pool_attr.hi_water = 4;
pool_attr.increment = 1;
pool_attr.maximum = 50;

The thread pool attributes tell the threads which functions to use for their blocking loop and control how many threads should be in existence at any time. We'll go into more detail on these attributes when we talk about multithreaded resource managers in more detail later in this guide.