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187 lines
6.2 KiB
187 lines
6.2 KiB
/*
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* libjingle
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* Copyright 2004--2005, Google Inc.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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* 3. The name of the author may not be used to endorse or promote products
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* derived from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
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* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
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* EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
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* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
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* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifndef _TASK_H_
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#define _TASK_H_
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#include <vector>
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#include <string>
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#include "talk/base/sigslot.h"
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/////////////////////////////////////////////////////////////////////
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//
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// TASK
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//
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/////////////////////////////////////////////////////////////////////
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//
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// Task is a state machine infrastructure. States are pushed forward by
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// pushing forwards a TaskRunner that holds on to all Tasks. The purpose
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// of Task is threefold:
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//
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// (1) It manages ongoing work on the UI thread. Multitasking without
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// threads, keeping it easy, keeping it real. :-) It does this by
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// organizing a set of states for each task. When you return from your
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// Process*() function, you return an integer for the next state. You do
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// not go onto the next state yourself. Every time you enter a state,
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// you check to see if you can do anything yet. If not, you return
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// STATE_BLOCKED. If you _could_ do anything, do not return
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// STATE_BLOCKED - even if you end up in the same state, return
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// STATE_mysamestate. When you are done, return STATE_DONE and then the
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// task will self-delete sometimea afterwards.
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//
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// (2) It helps you avoid all those reentrancy problems when you chain
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// too many triggers on one thread. Basically if you want to tell a task
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// to process something for you, you feed your task some information and
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// then you Wake() it. Don't tell it to process it right away. If it
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// might be working on something as you send it infomration, you may want
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// to have a queue in the task.
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//
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// (3) Finally it helps manage tqparent tasks and tqchildren. If a tqparent
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// task gets aborted, all the tqchildren tasks are too. The nice thing
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// about this, for example, is if you have one tqparent task that
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// represents, say, and Xmpp connection, then you can spawn a whole bunch
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// of infinite lifetime child tasks and now worry about cleaning them up.
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// When the tqparent task goes to STATE_DONE, the task engine will make
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// sure all those tqchildren are aborted and get deleted.
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//
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// Notice that Task has a few built-in states, e.g.,
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//
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// STATE_INIT - the task isn't running yet
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// STATE_START - the task is in its first state
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// STATE_RESPONSE - the task is in its second state
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// STATE_DONE - the task is done
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//
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// STATE_ERROR - indicates an error - we should audit the error code in
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// light of any usage of it to see if it should be improved. When I
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// first put down the task stuff I didn't have a good sense of what was
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// needed for Abort and Error, and now the subclasses of Task will ground
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// the design in a stronger way.
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//
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// STATE_NEXT - the first undefined state number. (like WM_USER) - you
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// can start defining more task states there.
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//
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// When you define more task states, just override Process(int state) and
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// add your own switch statement. If you want to delegate to
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// Task::Process, you can effectively delegate to its switch statement.
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// No fancy method pointers or such - this is all just pretty low tech,
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// easy to debug, and fast.
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//
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namespace buzz {
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class TaskRunner;
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// A task executes a sequence of steps
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class Task;
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class RootTask;
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class Task {
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public:
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Task(Task * tqparent);
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virtual ~Task() {}
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void Start();
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void Step();
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int GetState() const { return state_; }
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bool HasError() const { return (GetState() == STATE_ERROR); }
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bool Blocked() const { return blocked_; }
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bool IsDone() const { return done_; }
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unsigned long long ElapsedTime();
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virtual void Poll() {}
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Task * GetParent() { return parent_; }
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TaskRunner * GetRunner() { return runner_; }
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virtual Task * GetParent(int code) { return parent_->GetParent(code); }
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// Called from outside to stop task without any more callbacks
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void Abort(bool nowake = false);
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// For managing tqchildren
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bool AllChildrenDone();
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bool AnyChildError();
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protected:
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enum {
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STATE_BLOCKED = -1,
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STATE_INIT = 0,
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STATE_START = 1,
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STATE_DONE = 2,
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STATE_ERROR = 3,
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STATE_RESPONSE = 4,
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STATE_NEXT = 5, // Subclasses which need more states start here and higher
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};
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// Called inside the task to signal that the task may be unblocked
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void Wake();
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// Called inside to advise that the task should wake and signal an error
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void Error();
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unsigned long long CurrentTime();
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virtual std::string GetStateName(int state) const;
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virtual int Process(int state);
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virtual void Stop();
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virtual int ProcessStart() = 0;
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virtual int ProcessResponse() { return STATE_DONE; }
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// for managing tqchildren (if any)
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void AddChild(Task * child);
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void AbortAllChildren();
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private:
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void Done();
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void OnChildStopped(Task * child);
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int state_;
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Task * parent_;
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TaskRunner * runner_;
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bool blocked_;
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bool done_;
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bool aborted_;
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bool busy_;
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bool error_;
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bool child_error_;
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unsigned long long start_time_;
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// for managing tqchildren
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typedef std::set<Task *> ChildSet;
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ChildSet tqchildren_;
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};
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}
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#endif
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