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|
package runners
import (
"context"
"runtime"
"sync"
)
// WorkerFunc represents a function processable by a worker in WorkerPool. Note
// that implementations absolutely MUST check whether passed context is Done()
// otherwise stopping the pool may block for large periods of time.
type WorkerFunc func(context.Context)
// WorkerPool provides a means of enqueuing asynchronous work.
type WorkerPool struct {
queue chan WorkerFunc
free chan struct{}
wait sync.WaitGroup
svc Service
}
// NewWorkerPool returns a new WorkerPool with provided worker count and WorkerFunc queue size.
// The number of workers represents how many WorkerFuncs can be executed simultaneously, and the
// queue size represents the max number of WorkerFuncs that can be queued at any one time.
func NewWorkerPool(workers int, queue int) WorkerPool {
if workers < 1 {
workers = runtime.GOMAXPROCS(0)
}
if queue < 1 {
queue = workers * 2
}
return WorkerPool{
queue: make(chan WorkerFunc, queue),
free: make(chan struct{}, workers),
}
}
// Start will attempt to start the worker pool, asynchronously. Return is success state.
func (pool *WorkerPool) Start() bool {
ok := true
done := make(chan struct{})
go func() {
ok = pool.svc.Run(func(ctx context.Context) {
close(done)
pool.process(ctx)
})
if !ok {
close(done)
}
}()
<-done
return ok
}
// Stop will attempt to stop the worker pool, this will block until stopped. Return is success state.
func (pool *WorkerPool) Stop() bool {
return pool.svc.Stop()
}
// Running returns whether the worker pool is running.
func (pool *WorkerPool) Running() bool {
return pool.svc.Running()
}
// execute will take a queued function and pass it to a free worker when available.
func (pool *WorkerPool) execute(ctx context.Context, fn WorkerFunc) {
var acquired bool
// Set as running
pool.wait.Add(1)
select {
// Pool context cancelled
// (we fall through and let
// the function execute).
case <-ctx.Done():
// Free worker acquired.
case pool.free <- struct{}{}:
acquired = true
}
go func() {
defer func() {
// defer in case panic
if acquired {
<-pool.free
}
pool.wait.Done()
}()
// Run queued
fn(ctx)
}()
}
// process is the background processing routine that passes queued functions to workers.
func (pool *WorkerPool) process(ctx context.Context) {
for {
select {
// Pool context cancelled
case <-ctx.Done():
for {
select {
// Pop and execute queued
case fn := <-pool.queue:
fn(ctx) // ctx is closed
// Empty, wait for workers
default:
pool.wait.Wait()
return
}
}
// Queued func received
case fn := <-pool.queue:
pool.execute(ctx, fn)
}
}
}
// Enqueue will add provided WorkerFunc to the queue to be performed when there is a free worker.
// This will block until the function has been queued. 'fn' will ALWAYS be executed, even on pool
// close, which can be determined via context <-ctx.Done(). WorkerFuncs MUST respect the passed context.
func (pool *WorkerPool) Enqueue(fn WorkerFunc) {
// Check valid fn
if fn == nil {
return
}
select {
// Pool context cancelled
case <-pool.svc.Done():
fn(closedctx)
// Placed fn in queue
case pool.queue <- fn:
}
}
// EnqueueNoBlock attempts Enqueue but returns false if not executed.
func (pool *WorkerPool) EnqueueNoBlock(fn WorkerFunc) bool {
// Check valid fn
if fn == nil {
return false
}
select {
// Pool context cancelled
case <-pool.svc.Done():
return false
// Placed fn in queue
case pool.queue <- fn:
return true
// Queue is full
default:
return false
}
}
// Queue returns the number of currently queued WorkerFuncs.
func (pool *WorkerPool) Queue() int {
return len(pool.queue)
}
// Workers returns the number of currently active workers.
func (pool *WorkerPool) Workers() int {
return len(pool.free)
}
|
