ThreadLib Disk Scheduler

C++ systems project that builds a user-level thread library and applies it to a disk request scheduler. The thread library exposes thread_libinit, thread_create, thread_yield, locks, condition variables, signal, and broadcast. It uses ucontext to allocate per-thread stacks and switch execution without kernel threads. Interrupt enable/disable calls guard scheduler-critical sections, and the public interface includes start_preemptions for asynchronous or deterministic preemption testing.

Thread library Threads are represented with a context, stack pointer, finished flag, and id. A FIFO ready queue drives scheduling. thread_create builds a new context with its own stack and routes it through a core wrapper; thread_yield returns the current thread to the ready queue and switches through the scheduler context. Locks track an owner plus a FIFO wait queue, while condition variables keep per-condition wait queues and re-acquire the associated lock after wakeup.

Disk scheduler The disk simulator creates one requester thread per input file plus a service thread. Requesters submit tracks into a bounded shared disk queue and wait for confirmation before sending the next request. The service thread waits until enough requests are available, picks the next request with Shortest Seek Time First from the current head position, prints the service event, updates the last served track, and signals the requester and queue-capacity conditions.

Testing The repository includes many focused thread tests for initialization, yielding, locking, waiting, signaling, broadcast behavior, and preemption cases, along with disk input files and output logs for scheduler validation.