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Watcher.js
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Watcher.js
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const FSWatcher = require('fswatcher-child');
const Path = require('path');
/**
* This watcher wraps chokidar so that we watch directories rather than individual files on macOS.
* This prevents us from hitting EMFILE errors when running out of file descriptors.
* Chokidar does not have support for watching directories on non-macOS platforms, so we disable
* this behavior in order to prevent watching more individual files than necessary (e.g. node_modules).
*/
class Watcher {
constructor() {
// FS events on macOS are flakey in the tests, which write lots of files very quickly
// See https://github.com/paulmillr/chokidar/issues/612
this.shouldWatchDirs =
process.platform === 'darwin' && process.env.NODE_ENV !== 'test';
this.watcher = new FSWatcher({
useFsEvents: this.shouldWatchDirs,
ignoreInitial: true,
ignorePermissionErrors: true,
ignored: /\.cache|\.git/
});
this.watchedDirectories = new Map();
this.stopped = false;
}
/**
* Find a parent directory of `path` which is already watched
*/
getWatchedParent(path) {
path = Path.dirname(path);
let root = Path.parse(path).root;
while (path !== root) {
if (this.watchedDirectories.has(path)) {
return path;
}
path = Path.dirname(path);
}
return null;
}
/**
* Find a list of child directories of `path` which are already watched
*/
getWatchedChildren(path) {
path = Path.dirname(path) + Path.sep;
let res = [];
for (let dir of this.watchedDirectories.keys()) {
if (dir.startsWith(path)) {
res.push(dir);
}
}
return res;
}
/**
* Add a path to the watcher
*/
watch(path) {
if (this.shouldWatchDirs) {
// If there is no parent directory already watching this path, add a new watcher.
let parent = this.getWatchedParent(path);
if (!parent) {
// Find watchers on child directories, and remove them. They will be handled by the new parent watcher.
let children = this.getWatchedChildren(path);
let count = 1;
for (let dir of children) {
count += this.watchedDirectories.get(dir);
this.watcher._closePath(dir);
this.watchedDirectories.delete(dir);
}
let dir = Path.dirname(path);
this.watcher.add(dir);
this.watchedDirectories.set(dir, count);
} else {
// Otherwise, increment the reference count of the parent watcher.
this.watchedDirectories.set(
parent,
this.watchedDirectories.get(parent) + 1
);
}
} else {
this.watcher.add(path);
}
}
/**
* Remove a path from the watcher
*/
unwatch(path) {
if (this.shouldWatchDirs) {
let dir = this.getWatchedParent(path);
if (dir) {
// When the count of files watching a directory reaches zero, unwatch it.
let count = this.watchedDirectories.get(dir) - 1;
if (count === 0) {
this.watchedDirectories.delete(dir);
this.watcher.unwatch(dir);
} else {
this.watchedDirectories.set(dir, count);
}
}
} else {
this.watcher.unwatch(path);
}
}
/**
* Add an event handler
*/
on(event, callback) {
this.watcher.on(event, callback);
}
/**
* Add an event handler
*/
once(event, callback) {
this.watcher.once(event, callback);
}
/**
* Stop watching all paths
*/
async stop() {
this.stopped = true;
await this.watcher.close();
}
}
module.exports = Watcher;