Thread Library (Detailed Specification)

A C++ thread library designed to allow for writing multi-threaded programs on linux machines

Programming Interface

int thread_libinit(thread_startfunc_t func, void *arg)

thread_libinit initializes the thread library. A user program should call thread_libinit exactly once before calling any other thread functions.

int thread_create(thread_startfunc_t func, void *arg)

thread_create is used to create a new thread. When the newly created thread starts, it will call the function pointed to by func and pass it the single argument arg.

int thread_yield(void)

thread_yield causes the current thread to yield the CPU to the next runnable thread. It has no effect if there are no other runnable threads.

int thread_lock(unsigned int lock)
int thread_unlock(unsigned int lock)
int thread_wait(unsigned int lock, unsigned int cond)
int thread_signal(unsigned int lock, unsigned int cond)
int thread_broadcast(unsigned int lock, unsigned int cond)

thread_lock, thread_unlock, thread_wait, thread_signal, and thread_broadcast implement Mesa monitors in this thread library.

Each of these functions returns -1 on failure. Each of these functions returns 0 on success, except for thread_libinit, which does not return at all on success.

Error Handling

Here is a list of behaviors that are NOT considered errors:

• signaling without holding the lock (this is explicitly NOT an error in Mesa monitors)
• deadlock (however, trying to acquire a lock by a thread that already has the lock IS an error)
• a thread that exits while still holding a lock (the thread should keep the lock)

Disk Scheduler

The disk scheduler is sample program that simulates how an operating system gets and schedules disk I/Os for multiple threads. Threads issue disk requests by queueing them at the disk scheduler.

The program creates a number of requester threads to issue disk requests and 1 thread to service disk requests. Each requester thread must wait until the servicing thread finishes handling its last request before issuing its next request. A requester thread finishes after all the requests in its input file have been serviced.

Requests in the disk queue are NOT serviced in FIFO order but instead in SSTF order (shortest seek time first).

The service thread keeps the disk queue as full as possible to minimize average seek distance and only handles a request when the disk queue has the largest possible number of requests.

Running tests (On a linux machine)

./runtests.sh