opt: fall back to LeastTasks when RoundRobin can't find a worker (#306)

Besides, update a few comments and add new benchmarks for multi-pool

ants_benchmark_test.go

@@ -138,6 +138,24 @@ func BenchmarkAntsPool(b *testing.B) {
 	}
 }
 
+func BenchmarkAntsMultiPool(b *testing.B) {
+	var wg sync.WaitGroup
+	p, _ := NewMultiPool(10, PoolCap/10, RoundRobin, WithExpiryDuration(DefaultExpiredTime))
+	defer p.ReleaseTimeout(DefaultExpiredTime) //nolint:errcheck
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		wg.Add(RunTimes)
+		for j := 0; j < RunTimes; j++ {
+			_ = p.Submit(func() {
+				demoFunc()
+				wg.Done()
+			})
+		}
+		wg.Wait()
+	}
+}
+
 func BenchmarkGoroutinesThroughput(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		for j := 0; j < RunTimes; j++ {
@@ -170,3 +188,15 @@ func BenchmarkAntsPoolThroughput(b *testing.B) {
 		}
 	}
 }
+
+func BenchmarkAntsMultiPoolThroughput(b *testing.B) {
+	p, _ := NewMultiPool(10, PoolCap/10, RoundRobin, WithExpiryDuration(DefaultExpiredTime))
+	defer p.ReleaseTimeout(DefaultExpiredTime) //nolint:errcheck
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		for j := 0; j < RunTimes; j++ {
+			_ = p.Submit(demoFunc)
+		}
+	}
+}

multipool.go

@@ -44,7 +44,7 @@ const (
 // MultiPool consists of multiple pools, from which you will benefit the
 // performance improvement on basis of the fine-grained locking that reduces
 // the lock contention.
-// MultiPool is a good fit for the scenario that you have a large number of
+// MultiPool is a good fit for the scenario where you have a large number of
 // tasks to submit, and you don't want the single pool to be the bottleneck.
 type MultiPool struct {
 	pools []*Pool
@@ -70,8 +70,8 @@ func NewMultiPool(size, sizePerPool int, lbs LoadBalancingStrategy, options ...O
 	return &MultiPool{pools: pools, lbs: lbs}, nil
 }
 
-func (mp *MultiPool) next() (idx int) {
+func (mp *MultiPool) next(lbs LoadBalancingStrategy) (idx int) {
-	switch mp.lbs {
+	switch lbs {
 	case RoundRobin:
 		if idx = int((atomic.AddUint32(&mp.index, 1) - 1) % uint32(len(mp.pools))); idx == -1 {
 			idx = 0
@@ -91,11 +91,17 @@ func (mp *MultiPool) next() (idx int) {
 }
 
 // Submit submits a task to a pool selected by the load-balancing strategy.
-func (mp *MultiPool) Submit(task func()) error {
+func (mp *MultiPool) Submit(task func()) (err error) {
 	if mp.IsClosed() {
 		return ErrPoolClosed
 	}
-	return mp.pools[mp.next()].Submit(task)
+	if err = mp.pools[mp.next(mp.lbs)].Submit(task); err == nil {
+		return
+	}
+	if err == ErrPoolOverload && mp.lbs == RoundRobin {
+		return mp.pools[mp.next(LeastTasks)].Submit(task)
+	}
+	return
 }
 
 // Running returns the number of the currently running workers across all pools.

multipool_func.go

@@ -33,7 +33,7 @@ import (
 // MultiPoolWithFunc consists of multiple pools, from which you will benefit the
 // performance improvement on basis of the fine-grained locking that reduces
 // the lock contention.
-// MultiPoolWithFunc is a good fit for the scenario that you have a large number of
+// MultiPoolWithFunc is a good fit for the scenario where you have a large number of
 // tasks to submit, and you don't want the single pool to be the bottleneck.
 type MultiPoolWithFunc struct {
 	pools []*PoolWithFunc
@@ -59,8 +59,8 @@ func NewMultiPoolWithFunc(size, sizePerPool int, fn func(interface{}), lbs LoadB
 	return &MultiPoolWithFunc{pools: pools, lbs: lbs}, nil
 }
 
-func (mp *MultiPoolWithFunc) next() (idx int) {
+func (mp *MultiPoolWithFunc) next(lbs LoadBalancingStrategy) (idx int) {
-	switch mp.lbs {
+	switch lbs {
 	case RoundRobin:
 		if idx = int((atomic.AddUint32(&mp.index, 1) - 1) % uint32(len(mp.pools))); idx == -1 {
 			idx = 0
@@ -80,11 +80,18 @@ func (mp *MultiPoolWithFunc) next() (idx int) {
 }
 
 // Invoke submits a task to a pool selected by the load-balancing strategy.
-func (mp *MultiPoolWithFunc) Invoke(args interface{}) error {
+func (mp *MultiPoolWithFunc) Invoke(args interface{}) (err error) {
 	if mp.IsClosed() {
 		return ErrPoolClosed
 	}
-	return mp.pools[mp.next()].Invoke(args)
+
+	if err = mp.pools[mp.next(mp.lbs)].Invoke(args); err == nil {
+		return
+	}
+	if err == ErrPoolOverload && mp.lbs == RoundRobin {
+		return mp.pools[mp.next(LeastTasks)].Invoke(args)
+	}
+	return
 }
 
 // Running returns the number of the currently running workers across all pools.

pool.go

@@ -31,7 +31,8 @@ import (
 	syncx "github.com/panjf2000/ants/v2/internal/sync"
 )
 
-// Pool accepts the tasks from client, it limits the total of goroutines to a given number by recycling goroutines.
+// Pool accepts the tasks and process them concurrently,
+// it limits the total of goroutines to a given number by recycling goroutines.
 type Pool struct {
 	// capacity of the pool, a negative value means that the capacity of pool is limitless, an infinite pool is used to
 	// avoid potential issue of endless blocking caused by nested usage of a pool: submitting a task to pool
@@ -210,7 +211,7 @@ func NewPool(size int, options ...Option) (*Pool, error) {
 // Submit submits a task to this pool.
 //
 // Note that you are allowed to call Pool.Submit() from the current Pool.Submit(),
-// but what calls for special attention is that you will get blocked with the latest
+// but what calls for special attention is that you will get blocked with the last
 // Pool.Submit() call once the current Pool runs out of its capacity, and to avoid this,
 // you should instantiate a Pool with ants.WithNonblocking(true).
 func (p *Pool) Submit(task func()) error {
@@ -230,7 +231,7 @@ func (p *Pool) Running() int {
 	return int(atomic.LoadInt32(&p.running))
 }
 
-// Free returns the number of available goroutines to work, -1 indicates this pool is unlimited.
+// Free returns the number of available workers, -1 indicates this pool is unlimited.
 func (p *Pool) Free() int {
 	c := p.Cap()
 	if c < 0 {
@@ -239,7 +240,7 @@ func (p *Pool) Free() int {
 	return c - p.Running()
 }
 
-// Waiting returns the number of tasks which are waiting be executed.
+// Waiting returns the number of tasks waiting to be executed.
 func (p *Pool) Waiting() int {
 	return int(atomic.LoadInt32(&p.waiting))
 }
@@ -339,7 +340,7 @@ retry:
 		return
 	}
 
-	// If the worker queue is empty and we don't run out of the pool capacity,
+	// If the worker queue is empty, and we don't run out of the pool capacity,
 	// then just spawn a new worker goroutine.
 	if capacity := p.Cap(); capacity == -1 || capacity > p.Running() {
 		p.lock.Unlock()

pool_func.go

@@ -31,7 +31,7 @@ import (
 	syncx "github.com/panjf2000/ants/v2/internal/sync"
 )
 
-// PoolWithFunc accepts the tasks from client,
+// PoolWithFunc accepts the tasks and process them concurrently,
 // it limits the total of goroutines to a given number by recycling goroutines.
 type PoolWithFunc struct {
 	// capacity of the pool.
@@ -216,7 +216,7 @@ func NewPoolWithFunc(size int, pf func(interface{}), options ...Option) (*PoolWi
 // Invoke submits a task to pool.
 //
 // Note that you are allowed to call Pool.Invoke() from the current Pool.Invoke(),
-// but what calls for special attention is that you will get blocked with the latest
+// but what calls for special attention is that you will get blocked with the last
 // Pool.Invoke() call once the current Pool runs out of its capacity, and to avoid this,
 // you should instantiate a PoolWithFunc with ants.WithNonblocking(true).
 func (p *PoolWithFunc) Invoke(args interface{}) error {
@@ -236,7 +236,7 @@ func (p *PoolWithFunc) Running() int {
 	return int(atomic.LoadInt32(&p.running))
 }
 
-// Free returns the number of available goroutines to work, -1 indicates this pool is unlimited.
+// Free returns the number of available workers, -1 indicates this pool is unlimited.
 func (p *PoolWithFunc) Free() int {
 	c := p.Cap()
 	if c < 0 {
@@ -245,7 +245,7 @@ func (p *PoolWithFunc) Free() int {
 	return c - p.Running()
 }
 
-// Waiting returns the number of tasks which are waiting be executed.
+// Waiting returns the number of tasks waiting to be executed.
 func (p *PoolWithFunc) Waiting() int {
 	return int(atomic.LoadInt32(&p.waiting))
 }
@@ -345,7 +345,7 @@ retry:
 		return
 	}
 
-	// If the worker queue is empty and we don't run out of the pool capacity,
+	// If the worker queue is empty, and we don't run out of the pool capacity,
 	// then just spawn a new worker goroutine.
 	if capacity := p.Cap(); capacity == -1 || capacity > p.Running() {
 		p.lock.Unlock()