From 6d30f9e6fea7d451033653f8f167aef58f7f5347 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 13 Dec 2021 17:16:46 +0100
Subject: [PATCH 1/4] Explicitly make GC roots client sockets blocking

On macOS / BSD, these sockets inherit the non-blocking flag of the
server soocket, which is not what we want.

https://github.com/dotnet/runtime/issues/25069
https://bugs.python.org/issue7995

https://hydra.nixos.org/build/161439304
---
 src/libstore/gc.cc | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index 7a414da6b..ee123d84e 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -535,6 +535,12 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
                         }
                     });
 
+                    /* On macOS, accepted sockets inherit the
+                       non-blocking flag from the server socket, so
+                       explicitly make it blocking. */
+                    if (fcntl(fdServer.get(), F_SETFL, fcntl(fdServer.get(), F_GETFL) & ~O_NONBLOCK) == -1)
+                        abort();
+
                     while (true) {
                         try {
                             auto path = readLine(fdClient.get());

From 05fcc681ac07c4ea04b365e6b03a76f3e6c54c94 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 13 Dec 2021 16:14:57 +0100
Subject: [PATCH 2/4] Retry on ECONNREFUSED

https://hydra.nixos.org/build/161439235
---
 src/libstore/gc.cc | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index ee123d84e..fa68cd8f3 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -126,7 +126,17 @@ void LocalStore::addTempRoot(const StorePath & path)
             auto socketPath = stateDir.get() + gcSocketPath;
             debug("connecting to '%s'", socketPath);
             state->fdRootsSocket = createUnixDomainSocket();
-            nix::connect(state->fdRootsSocket.get(), socketPath);
+            try {
+                nix::connect(state->fdRootsSocket.get(), socketPath);
+            } catch (SysError & e) {
+                /* The garbage collector may have exited, so we need to
+                   restart. */
+                if (e.errNo == ECONNREFUSED) {
+                    debug("GC socket connection refused");
+                    state->fdRootsSocket.close();
+                    goto restart;
+                }
+            }
         }
 
         try {

From df1edd143fcb2532e32bbcb28f774ced1402cda4 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 13 Dec 2021 16:24:25 +0100
Subject: [PATCH 3/4] gc-non-blocking.sh: Don't hang indefinitely if the GC
 roots server crashes

---
 tests/gc-non-blocking.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/gc-non-blocking.sh b/tests/gc-non-blocking.sh
index 8b21c6f1c..0d781485d 100644
--- a/tests/gc-non-blocking.sh
+++ b/tests/gc-non-blocking.sh
@@ -19,7 +19,7 @@ pid=$!
 
 sleep 2
 
-outPath=$(nix-build -o "$TEST_ROOT/result" -E "
+outPath=$(nix-build --max-silent-time 60 -o "$TEST_ROOT/result" -E "
   with import ./config.nix;
   mkDerivation {
     name = \"non-blocking\";

From d17d46cfc2e38efb63565270a1fba7b03b37de16 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 13 Dec 2021 17:12:32 +0100
Subject: [PATCH 4/4] More debug info

---
 src/libstore/gc.cc | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index fa68cd8f3..e35199b3d 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -533,6 +533,8 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
                 AutoCloseFD fdClient = accept(fdServer.get(), nullptr, nullptr);
                 if (!fdClient) continue;
 
+                debug("GC roots server accepted new client");
+
                 /* Process the connection in a separate thread. */
                 auto fdClient_ = fdClient.get();
                 std::thread clientThread([&, fdClient = std::move(fdClient)]() {
@@ -575,7 +577,10 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
                             } else
                                 printError("received garbage instead of a root from client");
                             writeFull(fdClient.get(), "1", false);
-                        } catch (Error &) { break; }
+                        } catch (Error & e) {
+                            debug("reading GC root from client: %s", e.msg());
+                            break;
+                        }
                     }
                 });