[pbs-devel] [RFC proxmox-backup 3/5] ParallelHandler: add check_abort function and handle errors during join

[Stefan Reiter <s.reiter@proxmox.com>]

Enables outside functions to check if an error has occurred without
calling send. Also fix a potential bug where errors that happen after
the SendHandle has been dropped while doing the thread join might have
been ignored. Requires internal check_abort to be moved out of 'impl
SendHandle'.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
---
 src/tools/parallel_handler.rs | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/src/tools/parallel_handler.rs b/src/tools/parallel_handler.rs
index b15fc046..7b92c23a 100644
--- a/src/tools/parallel_handler.rs
+++ b/src/tools/parallel_handler.rs
@@ -10,19 +10,19 @@ pub struct SendHandle<I> {
     abort: Arc<Mutex<Option<String>>>,
 }
 
-impl<I: Send> SendHandle<I> {
-    /// Returns the first error happened, if any
-    pub fn check_abort(&self) -> Result<(), Error> {
-        let guard = self.abort.lock().unwrap();
-        if let Some(err_msg) = &*guard {
-            return Err(format_err!("{}", err_msg));
-        }
-        Ok(())
+/// Returns the first error happened, if any
+pub fn check_abort(abort: Arc<Mutex<Option<String>>>) -> Result<(), Error> {
+    let guard = abort.lock().unwrap();
+    if let Some(err_msg) = &*guard {
+        return Err(format_err!("{}", err_msg));
     }
+    Ok(())
+}
 
+impl<I: Send> SendHandle<I> {
     /// Send data to the worker threads
     pub fn send(&self, input: I) -> Result<(), Error> {
-        self.check_abort()?;
+        check_abort(Arc::clone(&self.abort))?;
         match self.input.send(input) {
             Ok(()) => Ok(()),
             Err(_) => bail!("send failed - channel closed"),
@@ -128,14 +128,23 @@ impl<'a, I: Send + 'static> ParallelHandler<'a, I> {
         Ok(())
     }
 
+    /// Return Err if at least one invocation of the callback failed
+    /// Panics if complete() has been called on this instance
+    pub fn check_abort(&self) -> Result<(), Error> {
+        check_abort(Arc::clone(&self.input.as_ref().unwrap().abort))
+    }
+
     /// Wait for worker threads to complete and check for errors
     pub fn complete(mut self) -> Result<(), Error> {
-        self.input.as_ref().unwrap().check_abort()?;
+        let abort = Arc::clone(&self.input.as_ref().unwrap().abort);
+        check_abort(Arc::clone(&abort))?;
         drop(self.input.take());
 
         let msg_list = self.join_threads();
 
         if msg_list.is_empty() {
+            // an error might be encountered while waiting for the join
+            check_abort(abort)?;
             return Ok(());
         }
         Err(format_err!("{}", msg_list.join("\n")))
-- 
2.20.1