migrated multi host connection pool from godropbox package

removing unneeded dependencies, which involved etcd versions.

weed/wdclient/resource_pool/managed_handle.go

@@ -0,0 +1,97 @@
+package resource_pool
+
+import (
+	"sync/atomic"
+
+	"errors"
+)
+
+// A resource handle managed by a resource pool.
+type ManagedHandle interface {
+	// This returns the handle's resource location.
+	ResourceLocation() string
+
+	// This returns the underlying resource handle (or error if the handle
+	// is no longer active).
+	Handle() (interface{}, error)
+
+	// This returns the resource pool which owns this handle.
+	Owner() ResourcePool
+
+	// The releases the underlying resource handle to the caller and marks the
+	// managed handle as inactive.  The caller is responsible for cleaning up
+	// the released handle.  This returns nil if the managed handle no longer
+	// owns the resource.
+	ReleaseUnderlyingHandle() interface{}
+
+	// This indictes a user is done with the handle and releases the handle
+	// back to the resource pool.
+	Release() error
+
+	// This indicates the handle is an invalid state, and that the
+	// connection should be discarded from the connection pool.
+	Discard() error
+}
+
+// A physical implementation of ManagedHandle
+type managedHandleImpl struct {
+	location string
+	handle   interface{}
+	pool     ResourcePool
+	isActive int32 // atomic bool
+	options  Options
+}
+
+// This creates a managed handle wrapper.
+func NewManagedHandle(
+	resourceLocation string,
+	handle interface{},
+	pool ResourcePool,
+	options Options) ManagedHandle {
+
+	h := &managedHandleImpl{
+		location: resourceLocation,
+		handle:   handle,
+		pool:     pool,
+		options:  options,
+	}
+	atomic.StoreInt32(&h.isActive, 1)
+
+	return h
+}
+
+// See ManagedHandle for documentation.
+func (c *managedHandleImpl) ResourceLocation() string {
+	return c.location
+}
+
+// See ManagedHandle for documentation.
+func (c *managedHandleImpl) Handle() (interface{}, error) {
+	if atomic.LoadInt32(&c.isActive) == 0 {
+		return c.handle, errors.New("Resource handle is no longer valid")
+	}
+	return c.handle, nil
+}
+
+// See ManagedHandle for documentation.
+func (c *managedHandleImpl) Owner() ResourcePool {
+	return c.pool
+}
+
+// See ManagedHandle for documentation.
+func (c *managedHandleImpl) ReleaseUnderlyingHandle() interface{} {
+	if atomic.CompareAndSwapInt32(&c.isActive, 1, 0) {
+		return c.handle
+	}
+	return nil
+}
+
+// See ManagedHandle for documentation.
+func (c *managedHandleImpl) Release() error {
+	return c.pool.Release(c)
+}
+
+// See ManagedHandle for documentation.
+func (c *managedHandleImpl) Discard() error {
+	return c.pool.Discard(c)
+}