Parallelize dirscan for grep.

src/engine/mod_regex.cpp

@@ -233,6 +233,15 @@ struct regex_grep_task
 		grep_tasks = b2::task::executor::get().make();
 	}
 
+	void dir_scan(value_ref dir)
+	{
+		grep_tasks->queue([this, dir] {
+			file_dirscan(dir,
+				reinterpret_cast<scanback>(&regex_grep_task::dirscan_callback),
+				this);
+		});
+	}
+
 	static void dirscan_callback(regex_grep_task * self,
 		OBJECT * path,
 		int found,
@@ -259,22 +268,17 @@ struct regex_grep_task
 			{
 				if (glob(glob_pattern->str(), filename.c_str()) == 0)
 				{
-					// We have a glob match for this file. We can queue it up
-					// for the possibly parallel grep.
-					grep_tasks->queue([this, filepath] {
-						auto filedata = file_preload(filepath);
-						file_grep(filepath, *filedata);
-					});
+					// We have a glob match for this file.
+					auto filedata = file_preload(filepath);
+					file_grep(filepath, *filedata);
 				}
 			}
 			return;
 		}
 		// Subdir, or equivalent. If indicated, recurse scan subdirectories.
 		if (recursive_glob)
 		{
-			file_dirscan(file,
-				reinterpret_cast<scanback>(&regex_grep_task::dirscan_callback),
-				this);
+			dir_scan(file);
 			return;
 		}
 	}
@@ -318,8 +322,11 @@ struct regex_grep_task
 		}
 
 		// Append this file's results to the global results.
-		scope_lock_t lock(mx);
-		intermediate.emplace_back(result.release());
+		if (!result->empty())
+		{
+			scope_lock_t lock(mx);
+			intermediate.emplace_back(result.release());
+		}
 	}
 
 	void wait() { grep_tasks->wait(); }
@@ -362,9 +369,7 @@ list_ref b2::regex_grep(list_cref directories,
 	regex_grep_task task(list_cref(*globs), patterns, sub_expr, options);
 	for (auto dir : directories)
 	{
-		file_dirscan(dir,
-			reinterpret_cast<scanback>(&regex_grep_task::dirscan_callback),
-			&task);
+		task.dir_scan(dir);
 	}
 	task.wait();