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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
//------------------------------------------------------------------------------
const 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) {
const list = context.segmentsList;
const normalizedBegin = begin >= 0 ? begin : list.length + begin;
const normalizedEnd = end >= 0 ? end : list.length + end;
const segments = [];
for (let i = 0; i < context.count; ++i) {
const allPrevSegments = [];
for (let j = normalizedBegin; j <= normalizedEnd; ++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) {
let currentSegments = segments;
while (currentSegments.length > context.count) {
const merged = [];
for (let i = 0, length = currentSegments.length / 2 | 0; i < length; ++i) {
merged.push(CodePathSegment.newNext(
context.idGenerator.next(),
[currentSegments[i], currentSegments[i + length]]
));
}
currentSegments = merged;
}
return currentSegments;
}
//------------------------------------------------------------------------------
// Public Interface
//------------------------------------------------------------------------------
/**
* A class to manage forking.
*/
class ForkContext {
/**
* @param {IdGenerator} idGenerator An identifier generator for segments.
* @param {ForkContext|null} upper An upper fork context.
* @param {number} count A number of parallel segments.
*/
constructor(idGenerator, upper, count) {
this.idGenerator = idGenerator;
this.upper = upper;
this.count = count;
this.segmentsList = [];
}
/**
* The head segments.
* @type {CodePathSegment[]}
*/
get head() {
const 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() {
const 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(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(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(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(segments) {
assert(segments.length >= this.count, `${segments.length} >= ${this.count}`);
this.segmentsList.push(mergeExtraSegments(this, segments));
}
/**
* Replaces the head segments with given segments.
* The current head segments are removed.
* @param {CodePathSegment[]} segments Segments to add.
* @returns {void}
*/
replaceHead(segments) {
assert(segments.length >= this.count, `${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(context) {
assert(context.count === this.count);
const source = context.segmentsList;
for (let i = 0; i < source.length; ++i) {
this.segmentsList.push(source[i]);
}
}
/**
* Clears all segments in this context.
* @returns {void}
*/
clear() {
this.segmentsList = [];
}
/**
* Creates the root fork context.
* @param {IdGenerator} idGenerator An identifier generator for segments.
* @returns {ForkContext} New fork context.
*/
static newRoot(idGenerator) {
const 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.
*/
static newEmpty(parentContext, forkLeavingPath) {
return new ForkContext(
parentContext.idGenerator,
parentContext,
(forkLeavingPath ? 2 : 1) * parentContext.count
);
}
}
module.exports = ForkContext;
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