ref: 6a113c23192c0877185aadddbc58b943ed68dd7b
dir: /lib/thread/rwlock.myr/
use "mutex" pkg thread = /* `_lock` grants exclusive access to either n readers or one writer. `_rlock` protects `_rcount` and allows the first reader to attempt to lock `_lockk` without letting other readers in. */ type rwlock = struct _lock : mutex _rlock : mutex _rcount : uint32 ;; const mkrwlock : (-> rwlock) const rdlock : (rw : rwlock# -> void) const wrlock : (rw : rwlock# -> void) const tryrdlock : (rw : rwlock# -> bool) const trywrlock : (rw : rwlock# -> bool) const rdunlock : (rw : rwlock# -> void) const wrunlock : (rw : rwlock# -> void) ;; const mkrwlock = { -> [._lock = mkmtx(), ._rlock = mkmtx()] } const rdlock = {rw mtxlock(&rw._rlock) /* The first reader either successfully acquires `_lock`, locking out all writers, or blocks while holding `_rlock`, locking out all other readers until it is able to acquire `_lock`, meaning that a writer has released it. */ if rw._rcount++ == 0 mtxlock(&rw._lock) ;; mtxunlock(&rw._rlock) } const wrlock = {rw mtxlock(&rw._lock) } const tryrdlock = {rw var rc = true mtxlock(&rw._rlock) if rw._rcount++ == 0 if !mtxtrylock(&rw._lock) rw._rcount-- rc = false ;; ;; mtxunlock(&rw._rlock) -> rc } const trywrlock = {rw -> mtxtrylock(&rw._lock) } const rdunlock = {rw mtxlock(&rw._rlock) /* `_lock` is not released until the last reader releases the lock. */ if --rw._rcount == 0 mtxunlock(&rw._lock) ;; mtxunlock(&rw._rlock) } const wrunlock = {rw mtxunlock(&rw._lock) }