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/**
* @fileoverview A class to operate forking.
*
* This is state of forking.
* This has a fork list and manages it.
*
* @author Toru Nagashima
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
var assert = require("assert"),
CodePathSegment = require("./code-path-segment");
//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------
/**
* Gets whether or not a given segment is reachable.
*
* @param {CodePathSegment} segment - A segment to get.
* @returns {boolean} `true` if the segment is reachable.
*/
function isReachable(segment) {
return segment.reachable;
}
/**
* Creates new segments from the specific range of `context.segmentsList`.
*
* When `context.segmentsList` is `[[a, b], [c, d], [e, f]]`, `begin` is `0`, and
* `end` is `-1`, this creates `[g, h]`. This `g` is from `a`, `c`, and `e`.
* This `h` is from `b`, `d`, and `f`.
*
* @param {ForkContext} context - An instance.
* @param {number} begin - The first index of the previous segments.
* @param {number} end - The last index of the previous segments.
* @param {function} create - A factory function of new segments.
* @returns {CodePathSegment[]} New segments.
*/
function makeSegments(context, begin, end, create) {
var list = context.segmentsList;
if (begin < 0) {
begin = list.length + begin;
}
if (end < 0) {
end = list.length + end;
}
var segments = [];
for (var i = 0; i < context.count; ++i) {
var allPrevSegments = [];
for (var j = begin; j <= end; ++j) {
allPrevSegments.push(list[j][i]);
}
segments.push(create(context.idGenerator.next(), allPrevSegments));
}
return segments;
}
/**
* `segments` becomes doubly in a `finally` block. Then if a code path exits by a
* control statement (such as `break`, `continue`) from the `finally` block, the
* destination's segments may be half of the source segments. In that case, this
* merges segments.
*
* @param {ForkContext} context - An instance.
* @param {CodePathSegment[]} segments - Segments to merge.
* @returns {CodePathSegment[]} The merged segments.
*/
function mergeExtraSegments(context, segments) {
while (segments.length > context.count) {
var merged = [];
for (var i = 0, length = segments.length / 2 | 0; i < length; ++i) {
merged.push(CodePathSegment.newNext(
context.idGenerator.next(),
[segments[i], segments[i + length]]
));
}
segments = merged;
}
return segments;
}
//------------------------------------------------------------------------------
// Public Interface
//------------------------------------------------------------------------------
/**
* A class to manage forking.
*
* @constructor
* @param {IdGenerator} idGenerator - An identifier generator for segments.
* @param {ForkContext|null} upper - An upper fork context.
* @param {number} count - A number of parallel segments.
*/
function ForkContext(idGenerator, upper, count) {
this.idGenerator = idGenerator;
this.upper = upper;
this.count = count;
this.segmentsList = [];
}
ForkContext.prototype = {
constructor: ForkContext,
/**
* The head segments.
* @type {CodePathSegment[]}
*/
get head() {
var list = this.segmentsList;
return list.length === 0 ? [] : list[list.length - 1];
},
/**
* A flag which shows empty.
* @type {boolean}
*/
get empty() {
return this.segmentsList.length === 0;
},
/**
* A flag which shows reachable.
* @type {boolean}
*/
get reachable() {
var segments = this.head;
return segments.length > 0 && segments.some(isReachable);
},
/**
* Creates new segments from this context.
*
* @param {number} begin - The first index of previous segments.
* @param {number} end - The last index of previous segments.
* @returns {CodePathSegment[]} New segments.
*/
makeNext: function(begin, end) {
return makeSegments(this, begin, end, CodePathSegment.newNext);
},
/**
* Creates new segments from this context.
* The new segments is always unreachable.
*
* @param {number} begin - The first index of previous segments.
* @param {number} end - The last index of previous segments.
* @returns {CodePathSegment[]} New segments.
*/
makeUnreachable: function(begin, end) {
return makeSegments(this, begin, end, CodePathSegment.newUnreachable);
},
/**
* Creates new segments from this context.
* The new segments don't have connections for previous segments.
* But these inherit the reachable flag from this context.
*
* @param {number} begin - The first index of previous segments.
* @param {number} end - The last index of previous segments.
* @returns {CodePathSegment[]} New segments.
*/
makeDisconnected: function(begin, end) {
return makeSegments(this, begin, end, CodePathSegment.newDisconnected);
},
/**
* Adds segments into this context.
* The added segments become the head.
*
* @param {CodePathSegment[]} segments - Segments to add.
* @returns {void}
*/
add: function(segments) {
assert(segments.length >= this.count, segments.length + " >= " + this.count);
this.segmentsList.push(mergeExtraSegments(this, segments));
},
/**
* Replaces the head segments with given segments.
* The current head segments are removed.
*
* @param {CodePathSegment[]} segments - Segments to add.
* @returns {void}
*/
replaceHead: function(segments) {
assert(segments.length >= this.count, segments.length + " >= " + this.count);
this.segmentsList.splice(-1, 1, mergeExtraSegments(this, segments));
},
/**
* Adds all segments of a given fork context into this context.
*
* @param {ForkContext} context - A fork context to add.
* @returns {void}
*/
addAll: function(context) {
assert(context.count === this.count);
var source = context.segmentsList;
for (var i = 0; i < source.length; ++i) {
this.segmentsList.push(source[i]);
}
},
/**
* Clears all secments in this context.
*
* @returns {void}
*/
clear: function() {
this.segmentsList = [];
}
};
/**
* Creates the root fork context.
*
* @param {IdGenerator} idGenerator - An identifier generator for segments.
* @returns {ForkContext} New fork context.
*/
ForkContext.newRoot = function(idGenerator) {
var context = new ForkContext(idGenerator, null, 1);
context.add([CodePathSegment.newRoot(idGenerator.next())]);
return context;
};
/**
* Creates an empty fork context preceded by a given context.
*
* @param {ForkContext} parentContext - The parent fork context.
* @param {boolean} forkLeavingPath - A flag which shows inside of `finally` block.
* @returns {ForkContext} New fork context.
*/
ForkContext.newEmpty = function(parentContext, forkLeavingPath) {
return new ForkContext(
parentContext.idGenerator,
parentContext,
(forkLeavingPath ? 2 : 1) * parentContext.count);
};
module.exports = ForkContext;