migrated multi host connection pool from godropbox package

removing unneeded dependencies, which involved etcd versions.

weed/wdclient/resource_pool/resource_pool.go

@@ -0,0 +1,96 @@
+package resource_pool
+
+import (
+	"time"
+)
+
+type Options struct {
+	// The maximum number of active resource handles per resource location.  (A
+	// non-positive value indicates the number of active resource handles is
+	// unbounded).
+	MaxActiveHandles int32
+
+	// The maximum number of idle resource handles per resource location that
+	// are kept alive by the resource pool.
+	MaxIdleHandles uint32
+
+	// The maximum amount of time an idle resource handle can remain alive (if
+	// specified).
+	MaxIdleTime *time.Duration
+
+	// This limits the number of concurrent Open calls (there's no limit when
+	// OpenMaxConcurrency is non-positive).
+	OpenMaxConcurrency int
+
+	// This function creates a resource handle (e.g., a connection) for a
+	// resource location.  The function must be thread-safe.
+	Open func(resourceLocation string) (
+		handle interface{},
+		err error)
+
+	// This function destroys a resource handle and performs the necessary
+	// cleanup to free up resources.  The function must be thread-safe.
+	Close func(handle interface{}) error
+
+	// This specifies the now time function.  When the function is non-nil, the
+	// resource pool will use the specified function instead of time.Now to
+	// generate the current time.
+	NowFunc func() time.Time
+}
+
+func (o Options) getCurrentTime() time.Time {
+	if o.NowFunc == nil {
+		return time.Now()
+	} else {
+		return o.NowFunc()
+	}
+}
+
+// A generic interface for managed resource pool.  All resource pool
+// implementations must be threadsafe.
+type ResourcePool interface {
+	// This returns the number of active resource handles.
+	NumActive() int32
+
+	// This returns the highest number of actives handles for the entire
+	// lifetime of the pool.  If the pool contains multiple sub-pools, the
+	// high water mark is the max of the sub-pools' high water marks.
+	ActiveHighWaterMark() int32
+
+	// This returns the number of alive idle handles.  NOTE: This is only used
+	// for testing.
+	NumIdle() int
+
+	// This associates a resource location to the resource pool; afterwhich,
+	// the user can get resource handles for the resource location.
+	Register(resourceLocation string) error
+
+	// This dissociates a resource location from the resource pool; afterwhich,
+	// the user can no longer get resource handles for the resource location.
+	// If the given resource location corresponds to a sub-pool, the unregistered
+	// sub-pool will enter lame duck mode.
+	Unregister(resourceLocation string) error
+
+	// This returns the list of registered resource location entries.
+	ListRegistered() []string
+
+	// This gets an active resource handle from the resource pool.  The
+	// handle will remain active until one of the following is called:
+	//  1. handle.Release()
+	//  2. handle.Discard()
+	//  3. pool.Release(handle)
+	//  4. pool.Discard(handle)
+	Get(key string) (ManagedHandle, error)
+
+	// This releases an active resource handle back to the resource pool.
+	Release(handle ManagedHandle) error
+
+	// This discards an active resource from the resource pool.
+	Discard(handle ManagedHandle) error
+
+	// Enter the resource pool into lame duck mode.  The resource pool
+	// will no longer return resource handles, and all idle resource handles
+	// are closed immediately (including active resource handles that are
+	// released back to the pool afterward).
+	EnterLameDuckMode()
+}