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minio/pkg/tasker/task.go

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3.3 KiB

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