1 files changed, 63 insertions, 0 deletions
diff --git a/balancer.go b/balancer.go
new file mode 100644
index 00000000..29fcd8d5
--- /dev/null
+++ b/balancer.go
@@ -0,0 +1,63 @@
+package roadrunner
+
+import (
+	"os/exec"
+	"sync"
+)
+
+// Balancer provides ability to perform hot-swap between 2 worker pools.
+type Balancer struct {
+	mu   sync.Mutex // protects pool hot swapping
+	pool *Pool      // pool to work for user commands
+}
+
+// Spawn initiates underlying pool of workers and replaced old one.
+func (b *Balancer) Spawn(cmd func() *exec.Cmd, factory Factory, cfg Config) error {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	var (
+		err error
+		old *Pool
+	)
+
+	old = b.pool
+	if b.pool, err = NewPool(cmd, factory, cfg); err != nil {
+		return err
+	}
+
+	if old != nil {
+		go func() {
+			old.Close()
+		}()
+	}
+
+	return nil
+}
+
+// Execute one task with given payload and context, returns result and context or error. Must not be used once pool is
+// being destroyed.
+func (b *Balancer) Execute(payload []byte, ctx interface{}) (resp []byte, rCtx []byte, err error) {
+	b.mu.Lock()
+	pool := b.pool
+	b.mu.Unlock()
+
+	return pool.Execute(payload, ctx)
+}
+
+// Workers return list of active workers.
+func (b *Balancer) Workers() []*Worker {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	return b.pool.Workers()
+}
+
+// Close closes underlying pool.
+func (b *Balancer) Close() {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	b.pool.Close()
+	b.pool = nil
+}