# std/threadpool

Dark Mode

- Manual
- Standard library
- Index
- Compiler docs
- Fusion docs
- devel, stable

Search:
Source Edit

Implements Nim's parallel & spawn statements.

Unstable API.

# See also

- threads module for basic thread support
- channels module for message passing support
- locks module for locks and condition variables
- asyncdispatch module for asynchronous IO

# Imports

cpuinfo, cpuload, locks, os

# Types

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

  A data flow variable. Source Edit

    FlowVarBase = ref FlowVarBaseObj

  Untyped base class for FlowVar[T]. Source Edit

    ThreadId = range[0 .. MaxDistinguishedThread - 1]

  A thread identifier. Source Edit

# Consts

    MaxDistinguishedThread = 32

  Maximum number of "distinguished" threads. Source Edit

    MaxThreadPoolSize = 256

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

# Procs

    proc `^`[T](fv: FlowVar[T]): T

  Blocks until the value is available and then returns this value. Source Edit

    proc awaitAndThen[T](fv: FlowVar[T]; action: proc (x: T) {.closure.})

  Blocks until `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 the ^ proc.

  Source Edit

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

  Waits until the value for `fv` arrives.

  Usually it is not necessary to call this explicitly.

  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 parallel(body: untyped) {.magic: "Parallel", ...raises: [], tags: [].}

  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 pinnedSpawn(id: ThreadId; call: sink typed) {.magic: "Spawn", ...raises: [],
        tags: [].}

  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 a proc call `p(...)` where `p` is gcsafe and has a return type that is either `void` or compatible with `FlowVar[T]`.

  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 the spawnX template instead.

  Source Edit

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

  Sets the maximum thread pool size. The default value of this is MaxThreadPoolSize. 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 spawn(call: sink typed) {.magic: "Spawn", ...raises: [], tags: [].}

  Always spawns a new task, so that the `call` is never executed on the calling thread.

  `call` has to be a proc call `p(...)` where `p` is gcsafe and has a return type that is either `void` or compatible with `FlowVar[T]`.

  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

    proc unsafeRead[T](fv: FlowVar[ref T]): ptr T

  Blocks until the value is available and then returns this value. Source Edit

# Templates

    template spawnX(call)

  Spawns a new task if a CPU core is ready, otherwise executes the call in the calling thread.

  Usually, it is advised to use the spawn proc in order to not block the producer for an unknown amount of time.

  `call` has to be a proc call `p(...)` where `p` is gcsafe and has a return type that is either 'void' or compatible with `FlowVar[T]`.

  Source Edit