# threadpool

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Implements Nim's spawn.

See also:

- threads module
- channels module
- locks module
- asyncdispatch module

# Imports

cpuinfo, cpuload, locks, os

# Types

    FlowVarBase = ref FlowVarBaseObj

  Untyped base class for `FlowVar[T]`. Source Edit

    FlowVar[T] {...}{.compilerProc.} = ref FlowVarObj[T]

  A data flow variable. Source Edit

    ThreadId = range[0 .. 32 - 1]

  Source Edit

# Consts

    MaxThreadPoolSize = 256

  Maximum size of the thread pool. 256 threads should be good enough for anybody ;-) Source Edit

    MaxDistinguishedThread = 32

  Maximum number of "distinguished" threads. Source Edit

# Procs

    proc blockUntil(fv: FlowVarBase) {...}{.raises: [], tags: [].}

  Waits until the value for the `fv` 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 so `awaitAndThen` can sometimes be more efficient than ^ proc.

  Source Edit

    proc unsafeRead[T](fv: FlowVar[ref T]): 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 blockUntilAny(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 `blockUntilAny` at the same time. That means if you `blockUntilAny([a,b])` and `blockUntilAny([b,c])` the second call will only block until `c`. If there is no `flowVar` left to be able to wait on, -1 is returned.

  Note: This results in non-deterministic behaviour and 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 minimum thread pool size. The default value of this is 4. Source Edit

    proc setMaxPoolSize(size: range[1 .. MaxThreadPoolSize]) {...}{.raises: [], tags: [].}

  Sets the maximum thread pool size. The default value of this is `MaxThreadPoolSize` (256). 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 template instead.

  Source Edit

    proc spawn(call: typed): void {...}{.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: typed): void {...}{.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: untyped) {...}{.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: [TimeEffect].}

  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): void

  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 proc 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