Adding upstream version 0.28.1.

Signed-off-by: Daniel Baumann <daniel@debian.org>

plugins/jsvm/pool.go

@@ -0,0 +1,73 @@
+package jsvm
+
+import (
+	"sync"
+
+	"github.com/dop251/goja"
+)
+
+type poolItem struct {
+	mux  sync.Mutex
+	busy bool
+	vm   *goja.Runtime
+}
+
+type vmsPool struct {
+	mux     sync.RWMutex
+	factory func() *goja.Runtime
+	items   []*poolItem
+}
+
+// newPool creates a new pool with pre-warmed vms generated from the specified factory.
+func newPool(size int, factory func() *goja.Runtime) *vmsPool {
+	pool := &vmsPool{
+		factory: factory,
+		items:   make([]*poolItem, size),
+	}
+
+	for i := 0; i < size; i++ {
+		vm := pool.factory()
+		pool.items[i] = &poolItem{vm: vm}
+	}
+
+	return pool
+}
+
+// run executes "call" with a vm created from the pool
+// (either from the buffer or a new one if all buffered vms are busy)
+func (p *vmsPool) run(call func(vm *goja.Runtime) error) error {
+	p.mux.RLock()
+
+	// try to find a free item
+	var freeItem *poolItem
+	for _, item := range p.items {
+		item.mux.Lock()
+		if item.busy {
+			item.mux.Unlock()
+			continue
+		}
+		item.busy = true
+		item.mux.Unlock()
+		freeItem = item
+		break
+	}
+
+	p.mux.RUnlock()
+
+	// create a new one-off item if of all of the pool items are currently busy
+	//
+	// note: if turned out not efficient we may change this in the future
+	// by adding the created item in the pool with some timer for removal
+	if freeItem == nil {
+		return call(p.factory())
+	}
+
+	execErr := call(freeItem.vm)
+
+	// "free" the vm
+	freeItem.mux.Lock()
+	freeItem.busy = false
+	freeItem.mux.Unlock()
+
+	return execErr
+}