6.033 Spring 2009 Robert Morris Lecture 7 ThreadsRemember: Send send(p, m): while true: acquire(p.lock) if p.in - p.out < N: p.buffer[p.in mod N] m p.in p.in + 1 release(p.lock) return release(p.lock)Send / Receive with Yield send(p, m): while true: if something to do: do it else: yield() receive(p): while true: if something to do: do it else: yield()yield(): acquire(t_lock) id = cpus[CPU()].thread threads[id].state = RUNNABLE threads[id].sp = SP do: id = (id + 1) mod N while threads[id].state != RUNNABLE threads[id].state = RUNNING SP = threads[id].sp cpus[CPU()].thread = id release(t_lock) suspend resume version 1Send with Yield send(p, m): while true: acquire(p.lock) if p.in - p.out < N: p.buffer[p.in mod N] m p.in p.in + 1 release(p.lock) return release(p.lock) yield()send(p, m): acquire(p.lock) while p.in - p.out == N: wait(p.notfull, p.lock) p.buffer[p.in mod N] m p.in p.in + 1 notify(p.notempty) release(p.lock) Send with Wait/Notifywait(cvar, lock): acquire(t_lock) release(lock) threads[id].cvar = cvar threads[id].state = WAITING yield() release(t_lock) acquire(lock)wait(cvar, lock): acquire(t_lock) release(lock) threads[id].cvar = cvar threads[id].state = WAITING yield() release(t_lock) acquire(lock) notify(cvar): acquire(t_lock) for i = 0 to N-1: if threads[i].cvar == cvar and threads[i].state == WAITING: threads[i].state = RUNNABLE release(t_lock)yield(): acquire(t_lock) id = cpus[CPU()].thread threads[id].state = RUNNABLE threads[id].sp = SP do: id = (id + 1) mod N while threads[id].state != RUNNABLE threads[id].state = RUNNING SP = threads[id].sp cpus[CPU()].thread = id release(t_lock) version 1 idle loopyield(): id = cpus[CPU()].thread threads[id].sp = SP SP = cpus[CPU()].stack do: id = (id + 1) mod N release(t_lock) acquire(t_lock) while threads[id].state != RUNNABLE threads[id].state = RUNNING SP = threads[id].sp cpus[CPU()].thread = id version 2 idle
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