From b50e39df578adc3f86c5efa16bee9035cfdab61b Mon Sep 17 00:00:00 2001
From: Sean Quah <8349537+squahtx@users.noreply.github.com>
Date: Thu, 2 Dec 2021 16:07:06 +0000
Subject: [PATCH] Avoid waiting for zombie processes in `synctl stop` (#11490)

---
 changelog.d/11490.feature |  1 +
 synctl                    | 19 ++++++++++++++++---
 2 files changed, 17 insertions(+), 3 deletions(-)
 create mode 100644 changelog.d/11490.feature

diff --git a/changelog.d/11490.feature b/changelog.d/11490.feature
new file mode 100644
index 0000000000..4cb97dc1d0
--- /dev/null
+++ b/changelog.d/11490.feature
@@ -0,0 +1 @@
+`synctl stop` will now wait for Synapse to exit before returning.
diff --git a/synctl b/synctl
index 08709f21ab..0e54f4847b 100755
--- a/synctl
+++ b/synctl
@@ -41,11 +41,24 @@ NORMAL = "\x1b[m"
 def pid_running(pid):
     try:
         os.kill(pid, 0)
-        return True
     except OSError as err:
         if err.errno == errno.EPERM:
-            return True
-        return False
+            pass  # process exists
+        else:
+            return False
+
+    # When running in a container, orphan processes may not get reaped and their
+    # PIDs may remain valid. Try to work around the issue.
+    try:
+        with open(f"/proc/{pid}/status") as status_file:
+            if "zombie" in status_file.read():
+                return False
+    except Exception:
+        # This isn't Linux or `/proc/` is unavailable.
+        # Assume that the process is still running.
+        pass
+
+    return True
 
 
 def write(message, colour=NORMAL, stream=sys.stdout):