On Sep 8, 2010, at 8:42 PM, cee1 wrote:
Questions: 1. How does a source's event handler accesses data returned by kevent?
Data returned by kevent will finally be recorded is ds_data field in _dispatch_source_latch_and_call. The event handler will be called with ds_handler_ctxt, which shoule be do_ctxt. "do_ctxt" can be set by function dispatch_set_context. The problem is: If a handler need to access ds_data, we have to set a proper do_ctxt (e.g. a do_ctxt of source). That's not convenient. It is only inconvenient if you're in the prototyping stage of a project. By the time a project matures, there will surely be a data structure that tracks a connection, and as a part of that connection, a pointer back to the dispatch_source_t. For example:
struct my_connection_s { ... dispatch_source_t source; ... }; ... void my_connection_handler(void *ctxt) { struct my_connection_s *mc = ctxt; printf("new data: %lu\n", dispatch_source_get_data(mc->source)); } ... struct my_connection_s *mc = my_connection_create(); mc->source = dispatch_source_create(...); dispatch_set_context(mc->source, mc); dispatch_source_set_event_handler_f(mc->source, my_connection_handler); dispatch_resume(mc->source); ...
"ds_data" is a member of dispatch_source_t, and dispatch_source_t is an opaque struct to client code. See the example above where dispatch_source_get_data() is used.
2. We have custom source of type DISPATCH_SOURCE_TYPE_DATA_ADD and DISPATCH_SOURCE_TYPE_DATA_OR, and can use dispatch_source_merge_data to fire custom sources. Why we don't have an 'is_level' source?
An "is_level" source may not make much sense, but can be attached with cancel handler, this may be useful in some cases.
If you can think of a practical use for that, then let us know. davez