perf: limit the number of concurrently open file watchers on macOS (#249)

Author: chenjiahan

lib/watchEventSource.js

@@ -13,8 +13,10 @@ const IS_OSX = require("os").platform() === "darwin";
 const IS_WIN = require("os").platform() === "win32";
 const SUPPORTS_RECURSIVE_WATCHING = IS_OSX || IS_WIN;
 
+// Use 20 for OSX to make `FSWatcher.close` faster
+// https://github.com/nodejs/node/issues/29949
 const watcherLimit =
-	+process.env.WATCHPACK_WATCHER_LIMIT || (IS_OSX ? 2000 : 10000);
+	+process.env.WATCHPACK_WATCHER_LIMIT || (IS_OSX ? 20 : 10000);
 
 const recursiveWatcherLogging = !!process.env
 	.WATCHPACK_RECURSIVE_WATCHER_LOGGING;
@@ -366,3 +368,4 @@ exports.getNumberOfWatchers = () => {
 };
 
 exports.createHandleChangeEvent = createHandleChangeEvent;
+exports.watcherLimit = watcherLimit;

test/ManyWatchers.js

@@ -6,6 +6,7 @@ const path = require("path");
 const TestHelper = require("./helpers/TestHelper");
 const Watchpack = require("../lib/watchpack");
 const watchEventSource = require("../lib/watchEventSource");
+const should = require("should");
 
 const fixtures = path.join(__dirname, "fixtures");
 const testHelper = new TestHelper(fixtures);
@@ -78,4 +79,11 @@ describe("ManyWatchers", function() {
 			});
 		});
 	});
+
+	it("should set the watcher limit based on the platform", () => {
+		should.equal(
+			watchEventSource.watcherLimit,
+			require("os").platform() === "darwin" ? 20 : 10000
+		);
+	});
 });