function createWatchedFileSet(interval, chunkSize) {
                if (interval === void 0) { interval = 2500; }
                if (chunkSize === void 0) { chunkSize = 30; }
                var watchedFiles = [];
                var nextFileToCheck = 0;
                var watchTimer;
                function getModifiedTime(fileName) {
                    return _fs.statSync(fileName).mtime;
                }
                function poll(checkedIndex) {
                    var watchedFile = watchedFiles[checkedIndex];
                    if (!watchedFile) {
                        return;
                    }
                    _fs.stat(watchedFile.fileName, function (err, stats) {
                        if (err) {
                            watchedFile.callback(watchedFile.fileName);
                        }
                        else if (watchedFile.mtime.getTime() !== stats.mtime.getTime()) {
                            watchedFile.mtime = getModifiedTime(watchedFile.fileName);
                            watchedFile.callback(watchedFile.fileName, watchedFile.mtime.getTime() === 0);
                        }
                    });
                }
                // this implementation uses polling and
                // stat due to inconsistencies of fs.watch
                // and efficiency of stat on modern filesystems
                function startWatchTimer() {
                    watchTimer = setInterval(function () {
                        var count = 0;
                        var nextToCheck = nextFileToCheck;
                        var firstCheck = -1;
                        while ((count < chunkSize) && (nextToCheck !== firstCheck)) {
                            poll(nextToCheck);
                            if (firstCheck < 0) {
                                firstCheck = nextToCheck;
                            }
                            nextToCheck++;
                            if (nextToCheck === watchedFiles.length) {
                                nextToCheck = 0;
                            }
                            count++;
                        }
                        nextFileToCheck = nextToCheck;
                    }, interval);
                }
                function addFile(fileName, callback) {
                    var file = {
                        fileName: fileName,
                        callback: callback,
                        mtime: getModifiedTime(fileName)
                    };
                    watchedFiles.push(file);
                    if (watchedFiles.length === 1) {
                        startWatchTimer();
                    }
                    return file;
                }
                function removeFile(file) {
                    watchedFiles = ts.copyListRemovingItem(file, watchedFiles);
                }
                return {
                    getModifiedTime: getModifiedTime,
                    poll: poll,
                    startWatchTimer: startWatchTimer,
                    addFile: addFile,
                    removeFile: removeFile
                };
            }