public walk(folderQueries: IFolderQuery[], extraFiles: URI[], onResult: (result: IRawFileMatch) => void, onMessage: (message: IProgress) => void, done: (error: Error, isLimitHit: boolean) => void): void {
		this.fileWalkSW = StopWatch.create(false);

		// Support that the file pattern is a full path to a file that exists
		if (this.isCanceled) {
			return done(null, this.isLimitHit);
		}

		// For each extra file
		if (extraFiles) {
			extraFiles.forEach(extraFilePath => {
				const basename = path.basename(extraFilePath.fsPath);
				if (this.globalExcludePattern && this.globalExcludePattern(extraFilePath.fsPath, basename)) {
					return; // excluded
				}

				// File: Check for match on file pattern and include pattern
				this.matchFile(onResult, { relativePath: extraFilePath.fsPath /* no workspace relative path */, basename });
			});
		}

		let traverse = this.nodeJSTraversal;
		if (!this.maxFilesize) {
			if (this.useRipgrep) {
				this.traversal = Traversal.Ripgrep;
				traverse = this.cmdTraversal;
			} else if (platform.isMacintosh) {
				this.traversal = Traversal.MacFind;
				traverse = this.cmdTraversal;
			} else if (platform.isLinux) {
				this.traversal = Traversal.LinuxFind;
				traverse = this.cmdTraversal;
			}
		}

		const isNodeTraversal = traverse === this.nodeJSTraversal;
		if (!isNodeTraversal) {
			this.cmdSW = StopWatch.create(false);
		}

		// For each root folder
		flow.parallel<IFolderQuery, void>(folderQueries, (folderQuery: IFolderQuery, rootFolderDone: (err: Error, result: void) => void) => {
			this.call(traverse, this, folderQuery, onResult, onMessage, (err?: Error) => {
				if (err) {
					const errorMessage = toErrorMessage(err);
					console.error(errorMessage);
					this.errors.push(errorMessage);
					rootFolderDone(err, undefined);
				} else {
					rootFolderDone(undefined, undefined);
				}
			});
		}, (errors, result) => {
			this.fileWalkSW.stop();
			const err = errors ? errors.filter(e => !!e)[0] : null;
			done(err, this.isLimitHit);
		});
	}

	walk(folderQueries: IFolderQuery[], extraFiles: URI[], onResult: (result: IRawFileMatch) => void, onMessage: (message: IProgressMessage) => void, done: (error: Error | null, isLimitHit: boolean) => void): void {
		this.fileWalkSW = StopWatch.create(false);

		// Support that the file pattern is a full path to a file that exists
		if (this.isCanceled) {
			return done(null, this.isLimitHit);
		}

		// For each extra file
		extraFiles.forEach(extraFilePath => {
			const basename = path.basename(extraFilePath.fsPath);
			if (this.globalExcludePattern && this.globalExcludePattern(extraFilePath.fsPath, basename)) {
				return; // excluded
			}

			// File: Check for match on file pattern and include pattern
			this.matchFile(onResult, { relativePath: extraFilePath.fsPath /* no workspace relative path */, basename });
		});

		this.cmdSW = StopWatch.create(false);

		// For each root folder
		flow.parallel<IFolderQuery, void>(folderQueries, (folderQuery: IFolderQuery, rootFolderDone: (err: Error | null, result: void) => void) => {
			this.call(this.cmdTraversal, this, folderQuery, onResult, onMessage, (err?: Error) => {
				if (err) {
					const errorMessage = toErrorMessage(err);
					console.error(errorMessage);
					this.errors.push(errorMessage);
					rootFolderDone(err, undefined);
				} else {
					rootFolderDone(null, undefined);
				}
			});
		}, (errors, result) => {
			this.fileWalkSW.stop();
			const err = errors ? arrays.coalesce(errors)[0] : null;
			done(err, this.isLimitHit);
		});
	}

	private doWalk(folderQuery: IFolderQuery, relativeParentPath: string, files: string[], onResult: (result: IRawFileMatch) => void, done: (error: Error) => void): void {
		const rootFolder = folderQuery.folder;

		// Execute tasks on each file in parallel to optimize throughput
		const hasSibling = glob.hasSiblingFn(() => files);
		flow.parallel(files, (file: string, clb: (error: Error, result: {}) => void): void => {

			// Check canceled
			if (this.isCanceled || this.isLimitHit) {
				return clb(null, undefined);
			}

			// Check exclude pattern
			// If the user searches for the exact file name, we adjust the glob matching
			// to ignore filtering by siblings because the user seems to know what she
			// is searching for and we want to include the result in that case anyway
			let currentRelativePath = relativeParentPath ? [relativeParentPath, file].join(path.sep) : file;
			if (this.folderExcludePatterns.get(folderQuery.folder.fsPath).test(currentRelativePath, file, this.config.filePattern !== file ? hasSibling : undefined)) {
				return clb(null, undefined);
			}

			// Use lstat to detect links
			let currentAbsolutePath = [rootFolder.fsPath, currentRelativePath].join(path.sep);
			fs.lstat(currentAbsolutePath, (error, lstat) => {
				if (error || this.isCanceled || this.isLimitHit) {
					return clb(null, undefined);
				}

				// If the path is a link, we must instead use fs.stat() to find out if the
				// link is a directory or not because lstat will always return the stat of
				// the link which is always a file.
				this.statLinkIfNeeded(currentAbsolutePath, lstat, (error, stat) => {
					if (error || this.isCanceled || this.isLimitHit) {
						return clb(null, undefined);
					}

					// Directory: Follow directories
					if (stat.isDirectory()) {
						this.directoriesWalked++;

						// to really prevent loops with links we need to resolve the real path of them
						return this.realPathIfNeeded(currentAbsolutePath, lstat, (error, realpath) => {
							if (error || this.isCanceled || this.isLimitHit) {
								return clb(null, undefined);
							}

							if (this.walkedPaths[realpath]) {
								return clb(null, undefined); // escape when there are cycles (can happen with symlinks)
							}

							this.walkedPaths[realpath] = true; // remember as walked

							// Continue walking
							return extfs.readdir(currentAbsolutePath, (error: Error, children: string[]): void => {
								if (error || this.isCanceled || this.isLimitHit) {
									return clb(null, undefined);
								}

								this.doWalk(folderQuery, currentRelativePath, children, onResult, err => clb(err, undefined));
							});
						});
					}

					// File: Check for match on file pattern and include pattern
					else {
						this.filesWalked++;
						if (currentRelativePath === this.filePattern) {
							return clb(null, undefined); // ignore file if its path matches with the file pattern because checkFilePatternRelativeMatch() takes care of those
						}

						if (this.maxFilesize && types.isNumber(stat.size) && stat.size > this.maxFilesize) {
							return clb(null, undefined); // ignore file if max file size is hit
						}

						this.matchFile(onResult, { base: rootFolder.fsPath, relativePath: currentRelativePath, basename: file, size: stat.size });
					}

					// Unwind
					return clb(null, undefined);
				});
			});
		}, (error: Error[]): void => {
			if (error) {
				error = arrays.coalesce(error); // find any error by removing null values first
			}

			return done(error && error.length > 0 ? error[0] : null);
		});
	}

		this.checkFilePatternAbsoluteMatch((exists, size) => {
			if (this.isCanceled) {
				return done(null, this.isLimitHit);
			}

			// Report result from file pattern if matching
			if (exists) {
				this.resultCount++;
				onResult({
					relativePath: this.filePattern,
					basename: path.basename(this.filePattern),
					size
				});

				// Optimization: a match on an absolute path is a good result and we do not
				// continue walking the entire root paths array for other matches because
				// it is very unlikely that another file would match on the full absolute path
				return done(null, this.isLimitHit);
			}

			// For each extra file
			if (extraFiles) {
				extraFiles.forEach(extraFilePath => {
					const basename = path.basename(extraFilePath);
					if (this.globalExcludePattern && this.globalExcludePattern(extraFilePath, basename)) {
						return; // excluded
					}

					// File: Check for match on file pattern and include pattern
					this.matchFile(onResult, { relativePath: extraFilePath /* no workspace relative path */, basename });
				});
			}

			let traverse = this.nodeJSTraversal;
			if (!this.maxFilesize) {
				if (this.useRipgrep) {
					this.traversal = Traversal.Ripgrep;
					traverse = this.cmdTraversal;
				} else if (platform.isMacintosh) {
					this.traversal = Traversal.MacFind;
					traverse = this.cmdTraversal;
					// Disable 'dir' for now (#11181, #11179, #11183, #11182).
				} /* else if (platform.isWindows) {
					this.traversal = Traversal.WindowsDir;
					traverse = this.windowsDirTraversal;
				} */ else if (platform.isLinux) {
					this.traversal = Traversal.LinuxFind;
					traverse = this.cmdTraversal;
				}
			}

			const isNodeTraversal = traverse === this.nodeJSTraversal;
			if (!isNodeTraversal) {
				this.cmdForkStartTime = Date.now();
			}

			// For each root folder
			flow.parallel<IFolderSearch, void>(folderQueries, (folderQuery: IFolderSearch, rootFolderDone: (err: Error, result: void) => void) => {
				this.call(traverse, this, folderQuery, onResult, onMessage, (err?: Error) => {
					if (err) {
						const errorMessage = toErrorMessage(err);
						console.error(errorMessage);
						this.errors.push(errorMessage);
						rootFolderDone(err, undefined);
					} else {
						rootFolderDone(undefined, undefined);
					}
				});
			}, (errors, result) => {
				const err = errors ? errors.filter(e => !!e)[0] : null;
				done(err, this.isLimitHit);
			});
		});