--- /dev/null
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2014 Red Hat
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation. See file COPYING.
+ *
+ */
+
+#include "include/Context.h"
+
+/**
+ * The Continuation interface is designed to help easily create multi-step
+ * operations that share data without having to pass it around or create
+ * custom Context classes for each step. To write a Continuation:
+ * 1) create a child class with a function for each stage.
+ * 2) Put all your shared data members into the class.
+ * 3) In the constructor, register each function stage with set_callback().
+ * 4) Whenever you need to provide a Context callback that activates the next
+ * stage, call get_callback(stage_number). If you need to proceed to another
+ * stage immediately, call immediate(stage, retcode) and return its result.
+ *
+ * To use a class:
+ * 1) Construct the child class on the heap.
+ * 2) Call begin().
+ * 3) The destructor will be called once one of your functions returns true to
+ * indicate it is done.
+ *
+ * Please note that while you can skip stages and get multiple Callback
+ * objects at once, you *cannot* have any stage report that the Continuation
+ * is completed while any other stage Callbacks are outstanding. It's best to
+ * be serial unless you want to maintain your own metadata about which stages
+ * are still pending.
+ *
+ * In fact, there are only two situations in which a stage should return
+ * true while others are running:
+ * 1) A Callback was issued and completed in the same thread,
+ * 2) you called immediate(stage) and it is returning true.
+ */
+
+class Continuation {
+ std::set<int> stages_in_flight;
+ std::set<int> stages_processing;
+ int rval;
+ Context *on_finish;
+ bool reported_done;
+
+ class Callback : public Context {
+ Continuation *continuation;
+ int stage_to_activate;
+ public:
+ Callback(Continuation *c, int stage) :
+ continuation(c),
+ stage_to_activate(stage) {}
+ void finish(int r) override {
+ continuation->continue_function(r, stage_to_activate);
+ }
+ };
+
+protected:
+ typedef bool (Continuation::*stagePtr)(int r);
+ /**
+ * Continue immediately to the given stage. It will be executed
+ * immediately, in the given thread.
+ * @pre You are in a callback function.
+ * @param stage The stage to execute
+ * @param r The return code that will be provided to the next stage
+ */
+ bool immediate(int stage, int r) {
+ assert(!stages_in_flight.count(stage));
+ assert(!stages_processing.count(stage));
+ stages_in_flight.insert(stage);
+ stages_processing.insert(stage);
+ return _continue_function(r, stage);
+ }
+
+ /**
+ * Obtain a Context * that when complete()ed calls back into the given stage.
+ * @pre You are in a callback function.
+ * @param stage The stage this Context should activate
+ */
+ Context *get_callback(int stage) {
+ stages_in_flight.insert(stage);
+ return new Callback(this, stage);
+ }
+
+ /**
+ * Set the return code that is passed to the finally-activated Context.
+ * @param new_rval The return code to use.
+ */
+ void set_rval(int new_rval) { rval = new_rval; }
+ int get_rval() { return rval; }
+
+ /**
+ * Register member functions as associated with a given stage. Start
+ * your stage IDs at 0 and make that one the setup phase.
+ * @pre There are no other functions associated with the stage.
+ * @param stage The stage to associate this function with
+ * @param func The function to use
+ */
+ void set_callback(int stage, stagePtr func) {
+ assert(callbacks.find(stage) == callbacks.end());
+ callbacks[stage] = func;
+ }
+
+ /**
+ * Called when the Continuation is done, as determined by a stage returning
+ * true and us having finished all the currently-processing ones.
+ */
+ virtual void _done() {
+ on_finish->complete(rval);
+ on_finish = NULL;
+ return;
+ }
+
+private:
+ std::map<int, Continuation::stagePtr> callbacks;
+
+ bool _continue_function(int r, int n) {
+ set<int>::iterator stage_iter = stages_in_flight.find(n);
+ assert(stage_iter != stages_in_flight.end());
+ assert(callbacks.count(n));
+ stagePtr p = callbacks[n];
+
+ pair<set<int>::iterator,bool> insert_r = stages_processing.insert(n);
+
+ bool done = (this->*p)(r);
+ if (done)
+ reported_done = true;
+
+ stages_processing.erase(insert_r.first);
+ stages_in_flight.erase(stage_iter);
+ return done;
+ }
+
+ void continue_function(int r, int stage) {
+ bool done = _continue_function(r, stage);
+
+ assert (!done ||
+ stages_in_flight.size() == stages_processing.size());
+
+ if (done ||
+ (reported_done && stages_processing.empty())) {
+ _done();
+ delete this;
+ }
+ }
+
+
+
+public:
+ /**
+ * Construct a new Continuation object. Call this from your child class,
+ * obviously.
+ *
+ * @Param c The Context which should be complete()ed when this Continuation
+ * is done.
+ */
+ Continuation(Context *c) :
+ rval(0), on_finish(c), reported_done(false) {}
+ /**
+ * Clean up.
+ */
+ virtual ~Continuation() { assert(on_finish == NULL); }
+ /**
+ * Begin running the Continuation.
+ */
+ void begin() { stages_in_flight.insert(0); continue_function(0, 0); }
+};
Code Review / stor4nfv.git / blobdiff