Threads and Polling

UCall creates no threads. Each loop has one application polling owner, and endpoint callbacks execute synchronously on that caller. Each batch endpoint has one polling owner, and its callbacks execute on the thread calling ucall_server_take_batch() or ucall_server_take_batches() with the handle its registration returned. A deadline cannot preempt a callback. One owner at a time may submit, poll, or free a client, on any thread. CPU classes select compiled string, cryptographic, and atomic kernels once, at initialization, under the requested class or the initialization thread’s capabilities. The application keeps those threads on CPUs supporting the selected class; serial is the conservative choice for differing capabilities. Server shutdown uses baseline atomics and native wakeups, so another thread can stop it without entering CPU-specific code.