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103 lines
3.3 KiB
103 lines
3.3 KiB
/*
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* Minio Cloud Storage, (C) 2015 Minio, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package tasker
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import (
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"container/list"
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"sync"
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)
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// NOTE: Task is a private entity. It is created and managed by TaskCtl
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// entirely. Only TaskCtl and Handle objects are exposed outside.
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// taskRef is a unique reference ID to a task. It is assigned by the
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// TaskCtl during the creation of a task. All tasfRef variables are
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// named "this".
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type taskRef *list.Element
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// Task is an abstract concept built on top of Go routines and
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// channels. Tasks themselves are expected to co-operate and comply with
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// the TaskCtl commands.
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type task struct {
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mutex *sync.Mutex
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this taskRef // Refence to task entry in the TaskCtl's task list.
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name string // Free form name.
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priority Command // Current priority.
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cmdCh chan Command // Channel to receive commands from TaskCtl.
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statusCh chan status // Channel to send completion status and error (if any) to TaskCtl.
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closeCh chan taskRef // Channel to notify the TaskCtl about ending this task.
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}
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// NewTask creates a new task structure and returns a handle to
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// it. Only the task controller has access to the task structure. The
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// caller routine only receives a handle to its task structure. Task
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// handle is like a reference to task self. Caller is expected to listen
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// for commands from the task controller and comply with it co-operatively.
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// this: Task reference is unique identifier assigned by the TaskCtl.
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// name: Free form name of the task. Eg. "Late Night Disk Scrubber".
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func newTask(name string) task {
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return task{
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// this: Is set by the TaskCtl's NewTask function.
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mutex: &sync.Mutex{},
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name: name,
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priority: CmdPriorityMedium,
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cmdCh: make(chan Command),
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statusCh: make(chan status),
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closeCh: make(chan taskRef),
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}
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}
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// getHandle returns a handle to the task. Handle has limited access to the task structure and it is safe to be exposed.
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func (t task) getHandle() Handle {
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t.mutex.Lock()
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defer t.mutex.Unlock()
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// Make a handle with limited access to channels (only send or receive).
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return Handle{
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cmdCh: t.cmdCh,
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statusCh: t.statusCh,
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closeCh: t.closeCh,
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}
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}
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// command method sends a command code to the task and returns its completion status.
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func (t task) command(cmd Command) status {
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t.mutex.Lock()
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defer t.mutex.Unlock()
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t.cmdCh <- cmd
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return <-t.statusCh
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}
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// close releases all the resources held by this task.
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func (t task) close() {
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t.mutex.Lock()
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defer t.mutex.Unlock()
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// Task can be ended in 2 ways.
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// 1) Calling application invokes Handle.Close().
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// 2) TaskCtl.Shutdown() ending the task's life.
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// In either case, task.close() is invoked only via the
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// TaskCtl. Handle.Close() only sends a message to the TaskCtl to
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// initiate a close call.
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close(t.cmdCh)
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close(t.statusCh)
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close(t.closeCh)
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}
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