371 lines
11 KiB
Nim
371 lines
11 KiB
Nim
#
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#
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# Nimrod's Runtime Library
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# (c) Copyright 2014 Andreas Rumpf
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#
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# See the file "copying.txt", included in this
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# distribution, for details about the copyright.
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#
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## Implements Nimrod's 'spawn'.
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import cpuinfo, cpuload, locks
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{.push stackTrace:off.}
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type
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CondVar = object
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c: TCond
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L: TLock
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counter: int
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proc createCondVar(): CondVar =
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initCond(result.c)
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initLock(result.L)
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proc destroyCondVar(cv: var CondVar) {.inline.} =
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deinitCond(cv.c)
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deinitLock(cv.L)
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proc await(cv: var CondVar) =
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acquire(cv.L)
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while cv.counter <= 0:
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wait(cv.c, cv.L)
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dec cv.counter
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release(cv.L)
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proc signal(cv: var CondVar) =
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acquire(cv.L)
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inc cv.counter
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release(cv.L)
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signal(cv.c)
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const CacheLineSize = 32 # true for most archs
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type
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Barrier {.compilerProc.} = object
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entered: int
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cv: CondVar # condvar takes 3 words at least
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when sizeof(int) < 8:
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cacheAlign: array[CacheLineSize-4*sizeof(int), byte]
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left: int
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cacheAlign2: array[CacheLineSize-sizeof(int), byte]
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interest: bool ## wether the master is interested in the "all done" event
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proc barrierEnter(b: ptr Barrier) {.compilerProc, inline.} =
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## due to the signaling between threads, it is ensured we are the only
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## one with access to 'entered' so we don't need 'atomicInc' here:
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inc b.entered
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proc barrierLeave(b: ptr Barrier) {.compilerProc, inline.} =
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atomicInc b.left
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if b.interest and b.left == b.entered: signal(b.cv)
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proc openBarrier(b: ptr Barrier) {.compilerProc, inline.} =
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b.entered = 0
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b.left = 0
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b.interest = false
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proc closeBarrier(b: ptr Barrier) {.compilerProc.} =
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if b.left != b.entered:
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b.cv = createCondVar()
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b.interest = true # XXX we really need to ensure no re-orderings are done
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# by the C compiler here
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while b.left != b.entered: await(b.cv)
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destroyCondVar(b.cv)
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{.pop.}
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# ----------------------------------------------------------------------------
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type
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foreign* = object ## a region that indicates the pointer comes from a
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## foreign thread heap.
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AwaitInfo = object
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cv: CondVar
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idx: int
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RawPromise* = ref RawPromiseObj ## untyped base class for 'Promise[T]'
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RawPromiseObj = object of TObject
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ready, usesCondVar: bool
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cv: CondVar #\
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# for 'awaitAny' support
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ai: ptr AwaitInfo
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idx: int
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data: pointer # we incRef and unref it to keep it alive
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owner: pointer # ptr Worker
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PromiseObj[T] = object of RawPromiseObj
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blob: T
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Promise*{.compilerProc.}[T] = ref PromiseObj[T]
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ToFreeQueue = object
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len: int
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lock: TLock
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empty: TCond
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data: array[512, pointer]
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WorkerProc = proc (thread, args: pointer) {.nimcall, gcsafe.}
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Worker = object
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taskArrived: CondVar
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taskStarted: CondVar #\
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# task data:
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f: WorkerProc
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data: pointer
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ready: bool # put it here for correct alignment!
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initialized: bool # whether it has even been initialized
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shutdown: bool # the pool requests to shut down this worker thread
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q: ToFreeQueue
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proc await*(prom: RawPromise) =
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## waits until the value for the promise arrives. Usually it is not necessary
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## to call this explicitly.
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if prom.usesCondVar:
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prom.usesCondVar = false
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await(prom.cv)
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destroyCondVar(prom.cv)
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proc finished(prom: RawPromise) =
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doAssert prom.ai.isNil, "promise is still attached to an 'awaitAny'"
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# we have to protect against the rare cases where the owner of the promise
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# simply disregards the promise and yet the "promiser" has not yet written
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# anything to it:
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await(prom)
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if prom.data.isNil: return
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let owner = cast[ptr Worker](prom.owner)
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let q = addr(owner.q)
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var waited = false
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while true:
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acquire(q.lock)
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if q.len < q.data.len:
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q.data[q.len] = prom.data
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inc q.len
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release(q.lock)
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break
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else:
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# the queue is exhausted! We block until it has been cleaned:
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release(q.lock)
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wait(q.empty, q.lock)
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waited = true
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prom.data = nil
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# wakeup other potentially waiting threads:
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if waited: signal(q.empty)
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proc cleanPromises(w: ptr Worker) =
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let q = addr(w.q)
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acquire(q.lock)
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for i in 0 .. <q.len:
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GC_unref(cast[PObject](q.data[i]))
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q.len = 0
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release(q.lock)
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signal(q.empty)
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proc promFinalizer[T](prom: Promise[T]) = finished(prom)
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proc nimCreatePromise[T](): Promise[T] {.compilerProc.} =
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new(result, promFinalizer)
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proc nimPromiseCreateCondVar(prom: RawPromise) {.compilerProc.} =
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prom.cv = createCondVar()
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prom.usesCondVar = true
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proc nimPromiseSignal(prom: RawPromise) {.compilerProc.} =
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if prom.ai != nil:
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acquire(prom.ai.cv.L)
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prom.ai.idx = prom.idx
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inc prom.ai.cv.counter
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release(prom.ai.cv.L)
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signal(prom.ai.cv.c)
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if prom.usesCondVar: signal(prom.cv)
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proc awaitAndThen*[T](prom: Promise[T]; action: proc (x: T) {.closure.}) =
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## blocks until the ``prom`` is available and then passes its value
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## to ``action``. Note that due to Nimrod's parameter passing semantics this
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## means that ``T`` doesn't need to be copied and so ``awaitAndThen`` can
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## sometimes be more efficient than ``^``.
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await(prom)
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when T is string or T is seq:
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action(cast[T](prom.data))
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elif T is ref:
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{.error: "'awaitAndThen' not available for Promise[ref]".}
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else:
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action(prom.blob)
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finished(prom)
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proc `^`*[T](prom: Promise[ref T]): foreign ptr T =
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## blocks until the value is available and then returns this value.
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await(prom)
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result = cast[foreign ptr T](prom.data)
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proc `^`*[T](prom: Promise[T]): T =
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## blocks until the value is available and then returns this value.
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await(prom)
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when T is string or T is seq:
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result = cast[T](prom.data)
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else:
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result = prom.blob
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proc awaitAny*(promises: openArray[RawPromise]): int =
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# awaits any of the given promises. Returns the index of one promise for which
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## a value arrived. A promise only supports one call to 'awaitAny' at the
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## same time. That means if you await([a,b]) and await([b,c]) the second
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## call will only await 'c'. If there is no promise left to be able to wait
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## on, -1 is returned.
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## **Note**: This results in non-deterministic behaviour and so should be
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## avoided.
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var ai: AwaitInfo
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ai.cv = createCondVar()
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var conflicts = 0
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for i in 0 .. promises.high:
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if cas(addr promises[i].ai, nil, addr ai):
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promises[i].idx = i
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else:
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inc conflicts
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if conflicts < promises.len:
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await(ai.cv)
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result = ai.idx
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for i in 0 .. promises.high:
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discard cas(addr promises[i].ai, addr ai, nil)
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else:
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result = -1
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destroyCondVar(ai.cv)
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proc nimArgsPassingDone(p: pointer) {.compilerProc.} =
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let w = cast[ptr Worker](p)
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signal(w.taskStarted)
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const
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MaxThreadPoolSize* = 256 ## maximal size of the thread pool. 256 threads
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## should be good enough for anybody ;-)
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var
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currentPoolSize: int
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maxPoolSize = MaxThreadPoolSize
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minPoolSize = 4
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gSomeReady = createCondVar()
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readyWorker: ptr Worker
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proc slave(w: ptr Worker) {.thread.} =
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while true:
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w.ready = true
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readyWorker = w
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signal(gSomeReady)
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await(w.taskArrived)
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assert(not w.ready)
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w.f(w, w.data)
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if w.q.len != 0: w.cleanPromises
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if w.shutdown:
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w.shutdown = false
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atomicDec currentPoolSize
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proc setMinPoolSize*(size: range[1..MaxThreadPoolSize]) =
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## sets the minimal thread pool size. The default value of this is 4.
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minPoolSize = size
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proc setMaxPoolSize*(size: range[1..MaxThreadPoolSize]) =
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## sets the minimal thread pool size. The default value of this
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## is ``MaxThreadPoolSize``.
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maxPoolSize = size
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var
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workers: array[MaxThreadPoolSize, TThread[ptr Worker]]
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workersData: array[MaxThreadPoolSize, Worker]
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proc activateThread(i: int) {.noinline.} =
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workersData[i].taskArrived = createCondVar()
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workersData[i].taskStarted = createCondVar()
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workersData[i].initialized = true
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initCond(workersData[i].q.empty)
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initLock(workersData[i].q.lock)
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createThread(workers[i], slave, addr(workersData[i]))
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proc setup() =
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currentPoolSize = min(countProcessors(), MaxThreadPoolSize)
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readyWorker = addr(workersData[0])
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for i in 0.. <currentPoolSize: activateThread(i)
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proc preferSpawn*(): bool =
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## Use this proc to determine quickly if a 'spawn' or a direct call is
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## preferable. If it returns 'true' a 'spawn' may make sense. In general
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## it is not necessary to call this directly; use 'spawnX' instead.
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result = gSomeReady.counter > 0
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proc spawn*(call: expr): expr {.magic: "Spawn".}
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## always spawns a new task, so that the 'call' is never executed on
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## the calling thread. 'call' has to be proc call 'p(...)' where 'p'
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## is gcsafe and has 'void' as the return type.
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template spawnX*(call: expr): expr =
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## spawns a new task if a CPU core is ready, otherwise executes the
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## call in the calling thread. Usually it is advised to
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## use 'spawn' in order to not block the producer for an unknown
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## amount of time. 'call' has to be proc call 'p(...)' where 'p'
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## is gcsafe and has 'void' as the return type.
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(if preferSpawn(): spawn call else: call)
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proc parallel*(body: stmt) {.magic: "Parallel".}
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## a parallel section can be used to execute a block in parallel. ``body``
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## has to be in a DSL that is a particular subset of the language. Please
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## refer to the manual for further information.
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var
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state: ThreadPoolState
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stateLock: TLock
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initLock stateLock
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proc selectWorker(w: ptr Worker; fn: WorkerProc; data: pointer): bool =
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if cas(addr w.ready, true, false):
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w.data = data
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w.f = fn
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signal(w.taskArrived)
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await(w.taskStarted)
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result = true
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proc nimSpawn(fn: WorkerProc; data: pointer) {.compilerProc.} =
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# implementation of 'spawn' that is used by the code generator.
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while true:
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if selectWorker(readyWorker, fn, data): return
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for i in 0.. <currentPoolSize:
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if selectWorker(addr(workersData[i]), fn, data): return
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# determine what to do, but keep in mind this is expensive too:
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# state.calls < maxPoolSize: warmup phase
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# (state.calls and 127) == 0: periodic check
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if state.calls < maxPoolSize or (state.calls and 127) == 0:
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# ensure the call to 'advice' is atomic:
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if tryAcquire(stateLock):
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case advice(state)
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of doNothing: discard
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of doCreateThread:
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if currentPoolSize < maxPoolSize:
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if not workersData[currentPoolSize].initialized:
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activateThread(currentPoolSize)
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let w = addr(workersData[currentPoolSize])
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atomicInc currentPoolSize
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if selectWorker(w, fn, data):
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release(stateLock)
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return
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# else we didn't succeed but some other thread, so do nothing.
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of doShutdownThread:
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if currentPoolSize > minPoolSize:
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let w = addr(workersData[currentPoolSize-1])
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w.shutdown = true
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# we don't free anything here. Too dangerous.
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release(stateLock)
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# else the acquire failed, but this means some
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# other thread succeeded, so we don't need to do anything here.
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await(gSomeReady)
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proc sync*() =
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## a simple barrier to wait for all spawn'ed tasks. If you need more elaborate
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## waiting, you have to use an explicit barrier.
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while true:
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var allReady = true
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for i in 0 .. <currentPoolSize:
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if not allReady: break
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allReady = allReady and workersData[i].ready
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if allReady: break
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await(gSomeReady)
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setup()
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