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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 <-ctx.Done()
// otherwise stopping the pool may block indefinitely.
type WorkerFunc func(context.Context)
// WorkerPool provides a means of enqueuing asynchronous work.
type WorkerPool struct {
fns chan WorkerFunc
svc Service
}
// Start will start the main WorkerPool management loop in a new goroutine, along
// with requested number of child worker goroutines. Returns false if already running.
func (pool *WorkerPool) Start(workers int, queue int) bool {
// Attempt to start the svc
ctx, ok := pool.svc.doStart()
if !ok {
return false
}
if workers < 1 {
// Use $GOMAXPROCS as default worker count
workers = runtime.GOMAXPROCS(0)
}
if queue < 0 {
// Set a reasonable queue default
queue = workers * 2
}
// Allocate pool queue of given size
fns := make(chan WorkerFunc, queue)
pool.fns = fns
go func() {
defer func() {
// unlock single wait
pool.svc.wait.Unlock()
// ensure stopped
pool.svc.Stop()
}()
var wait sync.WaitGroup
// Start goroutine worker functions
for i := 0; i < workers; i++ {
go func() {
// Trigger start / stop
wait.Add(1)
defer wait.Done()
// Keep workers running on panic
for !workerstart(ctx, fns) {
}
}()
}
// Set GC finalizer to stop pool on dealloc
runtime.SetFinalizer(pool, func(pool *WorkerPool) {
pool.svc.Stop()
})
// Wait on ctx
<-ctx.Done()
// Stop all workers
close(pool.fns)
wait.Wait()
}()
return true
}
// workerstart is the main worker runner routine, accepting functions from 'fns' until it is closed.
func workerstart(ctx context.Context, fns <-chan WorkerFunc) bool {
// Recover and drop any panic
defer func() { recover() }()
for {
// Wait on next func
fn, ok := <-fns
if !ok {
return true
}
// Run with ctx
fn(ctx)
}
}
// Stop will stop the WorkerPool management loop, blocking until stopped.
func (pool *WorkerPool) Stop() bool {
return pool.svc.Stop()
}
// Enqueue will add provided WorkerFunc to the queue to be performed when there is a free worker.
// This will block until function is queued or pool is stopped. In all cases, the WorkerFunc will be
// executed, with the state of the pool being indicated by <-ctx.Done() of the passed ctx.
// WorkerFuncs MUST respect the passed context.
func (pool *WorkerPool) Enqueue(fn WorkerFunc) {
// Check valid fn
if fn == nil {
return
}
select {
// Pool ctx cancelled
case <-pool.svc.Done():
fn(closedctx)
// Placed fn in queue
case pool.fns <- fn:
}
}
// EnqueueCtx is functionally identical to WorkerPool.Enqueue() but returns early in the
// case that caller provided <-ctx.Done() is closed, WITHOUT running the WorkerFunc.
func (pool *WorkerPool) EnqueueCtx(ctx context.Context, fn WorkerFunc) {
// Check valid fn
if fn == nil {
return
}
select {
// Caller ctx cancelled
case <-ctx.Done():
// Pool ctx cancelled
case <-pool.svc.Done():
fn(closedctx)
// Placed fn in queue
case pool.fns <- fn:
}
}
// EnqueueNow attempts Enqueue but returns false if not executed.
func (pool *WorkerPool) EnqueueNow(fn WorkerFunc) bool {
// Check valid fn
if fn == nil {
return false
}
select {
// Pool ctx cancelled
case <-pool.svc.Done():
return false
// Placed fn in queue
case pool.fns <- 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.fns)
}
|
