Module threadpool

Implements Nim's 'spawn'.

Types

foreign = object
a region that indicates the pointer comes from a foreign thread heap.   Source Edit
FlowVarBase = ref FlowVarBaseObj
untyped base class for 'FlowVar[T]'   Source Edit
FlowVar[T] = ref FlowVarObj[T]
a data flow variable   Source Edit
ThreadId = range[0 .. 32 - 1]
  Source Edit

Consts

MaxThreadPoolSize = 256
maximal size of the thread pool. 256 threads should be good enough for anybody ;-)   Source Edit
MaxDistinguishedThread = 32
maximal number of "distinguished" threads.   Source Edit

Procs

proc await(fv: FlowVarBase) {.
raises: [], tags: []
.}
waits until the value for the flowVar arrives. Usually it is not necessary to call this explicitly.   Source Edit
proc awaitAndThen[T](fv: FlowVar[T]; action: proc (x: T) {.
closure
.})
blocks until the fv is available and then passes its value to action. Note that due to Nim's parameter passing semantics this means that T doesn't need to be copied and so awaitAndThen can sometimes be more efficient than ^.   Source Edit
proc unsafeRead[T](fv: FlowVar[ref T]): foreign ptr T
blocks until the value is available and then returns this value.   Source Edit
proc `^`[T](fv: FlowVar[ref T]): ref T
blocks until the value is available and then returns this value.   Source Edit
proc `^`[T](fv: FlowVar[T]): T
blocks until the value is available and then returns this value.   Source Edit
proc awaitAny(flowVars: openArray[FlowVarBase]): int {.
raises: [], tags: []
.}
awaits any of the given flowVars. Returns the index of one flowVar for which a value arrived. A flowVar only supports one call to 'awaitAny' at the same time. That means if you await([a,b]) and await([b,c]) the second call will only await 'c'. If there is no flowVar left to be able to wait on, -1 is returned. Note: This results in non-deterministic behaviour and so should be avoided.   Source Edit
proc isReady(fv: FlowVarBase): bool {.
raises: [], tags: []
.}

Determines whether the specified FlowVarBase's value is available.

If true awaiting fv will not block.

  Source Edit
proc setMinPoolSize(size: range[1 .. MaxThreadPoolSize]) {.
raises: [], tags: []
.}
sets the minimal thread pool size. The default value of this is 4.   Source Edit
proc setMaxPoolSize(size: range[1 .. MaxThreadPoolSize]) {.
raises: [], tags: []
.}
sets the maximal thread pool size. The default value of this is MaxThreadPoolSize.   Source Edit
proc preferSpawn(): bool {.
raises: [], tags: []
.}
Use this proc to determine quickly if a 'spawn' or a direct call is preferable. If it returns 'true' a 'spawn' may make sense. In general it is not necessary to call this directly; use 'spawnX' instead.   Source Edit
proc spawn(call: expr): expr {.
magic: "Spawn"
.}
always spawns a new task, so that the 'call' is never executed on the calling thread. 'call' has to be proc call 'p(...)' where 'p' is gcsafe and has a return type that is either 'void' or compatible with FlowVar[T].   Source Edit
proc pinnedSpawn(id: ThreadId; call: expr): expr {.
magic: "Spawn"
.}
always spawns a new task on the worker thread with id, so that the 'call' is always executed on the thread. 'call' has to be proc call 'p(...)' where 'p' is gcsafe and has a return type that is either 'void' or compatible with FlowVar[T].   Source Edit
proc parallel(body: stmt) {.
magic: "Parallel"
.}
a parallel section can be used to execute a block in parallel. body has to be in a DSL that is a particular subset of the language. Please refer to the manual for further information.   Source Edit
proc sync() {.
raises: [], tags: []
.}
a simple barrier to wait for all spawn'ed tasks. If you need more elaborate waiting, you have to use an explicit barrier.   Source Edit

Templates

template spawnX(call: expr): expr
spawns a new task if a CPU core is ready, otherwise executes the call in the calling thread. Usually it is advised to use 'spawn' in order to not block the producer for an unknown amount of time. 'call' has to be proc call 'p(...)' where 'p' is gcsafe and has a return type that is either 'void' or compatible with FlowVar[T].   Source Edit