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
Types
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 spawned 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