From a1b4bc7292c3349baef0c6270798f1a36b63516b Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 20 Jan 2025 13:22:50 +0100
Subject: [PATCH] processGraph(): Don't throw ThreadPoolShutDown if there is an
 exception

Fixes

  $ nix copy --derivation --to /tmp/nix /nix/store/...
  error: cannot enqueue a work item while the thread pool is shutting down

The ThreadPoolShutDown exception was hiding the reason for the thread
pool shut down, e.g.

  error: cannot add path '/nix/store/03sl46khd8gmjpsad7223m32ma965vy9-fix-static.patch' because it lacks a signature by a trusted key

(cherry picked from commit a8c69cc907044565f9e43371663cc8315602b28a)
---
 src/libutil/thread-pool.hh | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/libutil/thread-pool.hh b/src/libutil/thread-pool.hh
index dc056481a..4adc48657 100644
--- a/src/libutil/thread-pool.hh
+++ b/src/libutil/thread-pool.hh
@@ -150,8 +150,16 @@ void processGraph(
         }
     };
 
-    for (auto & node : nodes)
-        pool.enqueue(std::bind(worker, std::ref(node)));
+    for (auto & node : nodes) {
+        try {
+            pool.enqueue(std::bind(worker, std::ref(node)));
+        } catch (ThreadPoolShutDown &) {
+            /* Stop if the thread pool is shutting down. It means a
+               previous work item threw an exception, so process()
+               below will rethrow it. */
+            break;
+        }
+    }
 
     pool.process();