Group together output from multi exec commands

So that if multiple `--exec` options are given, and the commands are run
in parallel, the buffered output for related commands will be
consecutive.

src/exec/command.rs

@@ -6,12 +6,57 @@ use std::sync::Mutex;
 use crate::error::print_error;
 use crate::exit_codes::ExitCode;
 
+struct Outputs {
+    stdout: Vec<u8>,
+    stderr: Vec<u8>,
+}
+struct OutputBuf<'a> {
+    out_perm: &'a Mutex<()>,
+    outputs: Vec<Outputs>,
+}
+
+impl<'a> OutputBuf<'a> {
+    fn new(out_perm: &'a Mutex<()>) -> Self {
+        Self {
+            out_perm,
+            outputs: Vec::new(),
+        }
+    }
+
+    fn push(&mut self, stdout: Vec<u8>, stderr: Vec<u8>) {
+        self.outputs.push(Outputs { stdout, stderr });
+    }
+
+    fn write(self) {
+        // avoid taking the lock if there is nothing to do
+        if self.outputs.is_empty() {
+            return;
+        }
+        // While this lock is active, this thread will be the only thread allowed
+        // to write its outputs.
+        let _lock = self.out_perm.lock().unwrap();
+
+        let stdout = io::stdout();
+        let stderr = io::stderr();
+
+        let mut stdout = stdout.lock();
+        let mut stderr = stderr.lock();
+
+        for output in self.outputs.iter() {
+            let _ = stdout.write_all(&output.stdout);
+            let _ = stderr.write_all(&output.stderr);
+        }
+    }
+}
+
 /// Executes a command.
-pub fn execute_command(
+pub fn execute_commands<I: Iterator<Item = Command>>(
-    mut cmd: Command,
+    cmds: I,
     out_perm: &Mutex<()>,
     enable_output_buffering: bool,
 ) -> ExitCode {
+    let mut out_buf = OutputBuf::new(out_perm);
+    for mut cmd in cmds {
         // Spawn the supplied command.
         let output = if enable_output_buffering {
             cmd.output()
@@ -24,29 +69,30 @@ pub fn execute_command(
         // Then wait for the command to exit, if it was spawned.
         match output {
             Ok(output) => {
-            // While this lock is active, this thread will be the only thread allowed
+                if enable_output_buffering {
-            // to write its outputs.
+                    out_buf.push(output.stdout, output.stderr);
-            let _lock = out_perm.lock().unwrap();
-
-            let stdout = io::stdout();
-            let stderr = io::stderr();
-
-            let _ = stdout.lock().write_all(&output.stdout);
-            let _ = stderr.lock().write_all(&output.stderr);
-
-            if output.status.code() == Some(0) {
-                ExitCode::Success
-            } else {
-                ExitCode::GeneralError
                 }
+                if output.status.code() != Some(0) {
+                    out_buf.write();
+                    return ExitCode::GeneralError;
                 }
-        Err(ref why) if why.kind() == io::ErrorKind::NotFound => {
-            print_error(format!("Command not found: {:?}", cmd));
-            ExitCode::GeneralError
             }
             Err(why) => {
-            print_error(format!("Problem while executing command: {}", why));
+                out_buf.write();
+                return handle_cmd_error(&cmd, why);
+            }
+        }
+    }
+    out_buf.write();
+    ExitCode::Success
+}
+
+pub fn handle_cmd_error(cmd: &Command, err: io::Error) -> ExitCode {
+    if err.kind() == io::ErrorKind::NotFound {
+        print_error(format!("Command not found: {:?}", cmd));
+        ExitCode::GeneralError
+    } else {
+        print_error(format!("Problem while executing command: {}", err));
         ExitCode::GeneralError
     }
-    }
 }

src/exec/job.rs

@@ -49,7 +49,6 @@ pub fn batch(
     rx: Receiver<WorkerResult>,
     cmd: &CommandSet,
     show_filesystem_errors: bool,
-    buffer_output: bool,
     limit: usize,
 ) -> ExitCode {
     let paths = rx.iter().filter_map(|value| match value {
@@ -63,14 +62,14 @@ pub fn batch(
     });
     if limit == 0 {
         // no limit
-        return cmd.execute_batch(paths, buffer_output);
+        return cmd.execute_batch(paths);
     }
 
     let mut exit_codes = Vec::new();
     let mut peekable = paths.peekable();
     while peekable.peek().is_some() {
         let limited = peekable.by_ref().take(limit);
-        let exit_code = cmd.execute_batch(limited, buffer_output);
+        let exit_code = cmd.execute_batch(limited);
         exit_codes.push(exit_code);
     }
     merge_exitcodes(exit_codes)

src/exec/mod.rs

@@ -15,7 +15,7 @@ use regex::Regex;
 
 use crate::exit_codes::ExitCode;
 
-use self::command::execute_command;
+use self::command::{execute_commands, handle_cmd_error};
 use self::input::{basename, dirname, remove_extension};
 pub use self::job::{batch, job};
 use self::token::Token;
@@ -86,17 +86,14 @@ impl CommandSet {
         buffer_output: bool,
     ) -> ExitCode {
         let path_separator = self.path_separator.as_deref();
-        for cmd in &self.commands {
+        let commands = self
-            let exit =
+            .commands
-                cmd.generate_and_execute(input, path_separator, &mut out_perm, buffer_output);
+            .iter()
-            if exit != ExitCode::Success {
+            .map(|c| c.generate(input, path_separator));
-                return exit;
+        execute_commands(commands, &mut out_perm, buffer_output)
-            }
-        }
-        ExitCode::Success
     }
 
-    pub fn execute_batch<I>(&self, paths: I, buffer_output: bool) -> ExitCode
+    pub fn execute_batch<I>(&self, paths: I) -> ExitCode
     where
         I: Iterator<Item = PathBuf>,
     {
@@ -104,7 +101,7 @@ impl CommandSet {
         let mut paths = paths.collect::<Vec<_>>();
         paths.sort();
         for cmd in &self.commands {
-            let exit = cmd.generate_and_execute_batch(&paths, path_separator, buffer_output);
+            let exit = cmd.generate_and_execute_batch(&paths, path_separator);
             if exit != ExitCode::Success {
                 return exit;
             }
@@ -189,27 +186,19 @@ impl CommandTemplate {
     /// Generates and executes a command.
     ///
     /// Using the internal `args` field, and a supplied `input` variable, a `Command` will be
-    /// build. Once all arguments have been processed, the command is executed.
+    /// build.
-    fn generate_and_execute(
+    fn generate(&self, input: &Path, path_separator: Option<&str>) -> Command {
-        &self,
-        input: &Path,
-        path_separator: Option<&str>,
-        out_perm: &mut Arc<Mutex<()>>,
-        buffer_output: bool,
-    ) -> ExitCode {
         let mut cmd = Command::new(self.args[0].generate(&input, path_separator));
         for arg in &self.args[1..] {
             cmd.arg(arg.generate(&input, path_separator));
         }
-
+        cmd
-        execute_command(cmd, out_perm, buffer_output)
     }
 
     fn generate_and_execute_batch(
         &self,
         paths: &[PathBuf],
         path_separator: Option<&str>,
-        buffer_output: bool,
     ) -> ExitCode {
         let mut cmd = Command::new(self.args[0].generate("", None));
         cmd.stdin(Stdio::inherit());
@@ -230,7 +219,10 @@ impl CommandTemplate {
         }
 
         if has_path {
-            execute_command(cmd, &Mutex::new(()), buffer_output)
+            match cmd.spawn().and_then(|mut c| c.wait()) {
+                Ok(_) => ExitCode::Success,
+                Err(e) => handle_cmd_error(&cmd, e),
+            }
         } else {
             ExitCode::Success
         }

src/walk.rs

@@ -350,13 +350,7 @@ fn spawn_receiver(
         // This will be set to `Some` if the `--exec` argument was supplied.
         if let Some(ref cmd) = config.command {
             if cmd.in_batch_mode() {
-                exec::batch(
+                exec::batch(rx, cmd, show_filesystem_errors, config.batch_size)
-                    rx,
-                    cmd,
-                    show_filesystem_errors,
-                    enable_output_buffering,
-                    config.batch_size,
-                )
             } else {
                 let shared_rx = Arc::new(Mutex::new(rx));