feat: add tryacquire function

Adds a TryAcquire function, which will attempt to acquire a lock if slots are available. A boolean
indicating wether a slot was acquired is returned.

closes #6

semaphore.go

@@ -3,6 +3,7 @@ package semaphore
 import (
 	"context"
 	"fmt"
+	"time"
 
 	"github.com/eapache/channels"
 )
@@ -31,6 +32,21 @@ func (r *ResizableSemaphore) Acquire(ctx context.Context) error {
 	}
 }
 
+// TryAcquire will acquire a slot if any are available. A boolean indicating whether or not a slot was acquired is returned.
+func (r *ResizableSemaphore) TryAcquire() bool {
+	// Configure a small timeout in case the final semaphore is acquired after the check and before
+	// this function acquires a semaphore.
+	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Millisecond)
+	defer cancel()
+	if r.Len() < r.Cap() {
+		if err := r.Acquire(ctx); err == nil {
+			return true
+		}
+	}
+
+	return false
+}
+
 // Release frees up a slot.
 func (r *ResizableSemaphore) Release() {
 	<-r.ch.Out()

semaphore_test.go

@@ -109,3 +109,24 @@ func TestAcquire(t *testing.T) {
 		a.ErrorIs(err, context.Canceled)
 	})
 }
+
+func TestTryAcquire(t *testing.T) {
+	a := assert.New(t)
+
+	t.Run("Successful", func(t *testing.T) {
+		r := New(1)
+
+		a.True(r.TryAcquire())
+		defer r.Release()
+	})
+
+	t.Run("Failure", func(t *testing.T) {
+		r := New(1)
+
+		ctx := context.Background()
+		a.NoError(r.Acquire(ctx))
+
+		defer r.Release()
+		a.False(r.TryAcquire())
+	})
+}