From 0a2c63de3c508b90d168604f2a5bc1345a12f4c9 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Mon, 28 Jan 2019 13:10:22 +0200
Subject: Fix race in QEMU shutdown

---
 bbot/agent/machine.cxx | 18 ++++++++++++++----
 bbot/agent/machine.hxx |  8 ++++----
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/bbot/agent/machine.cxx b/bbot/agent/machine.cxx
index 69ef3c7..fdc11c0 100644
--- a/bbot/agent/machine.cxx
+++ b/bbot/agent/machine.cxx
@@ -378,8 +378,16 @@ namespace bbot
     }
     catch (const system_error& e)
     {
-      size_t t (0);
-      if (wait (t))
+      // There is a window between QEMU closing the monitor socket and exiting
+      // so we wait but only briefly.
+      //
+      size_t t (seconds > 0 ? 1 : 0);
+
+      seconds -= t;
+      bool r (wait (t));
+      seconds += t;
+
+      if (r)
         return true;
 
       fail << "unable to communicate with qemu monitor: " << e;
@@ -391,13 +399,15 @@ namespace bbot
   void kvm_machine::
   forcedown (bool fh)
   {
+    // Similar logic to shutdown().
+    //
     try
     {
       monitor_command ("system_reset");
     }
     catch (const system_error& e)
     {
-      size_t t (0);
+      size_t t (1);
       if (wait (t, fh))
         return;
 
@@ -450,7 +460,7 @@ namespace bbot
     }
     catch (const process_error& e)
     {
-      fail (fh) << "unable to execute " << kvm << ": " << e << endf;
+      fail (fh) << "unable to wait for " << kvm << ": " << e << endf;
     }
   }
 
diff --git a/bbot/agent/machine.hxx b/bbot/agent/machine.hxx
index b1ad874..04da80e 100644
--- a/bbot/agent/machine.hxx
+++ b/bbot/agent/machine.hxx
@@ -38,10 +38,10 @@ namespace bbot
     virtual void
     suspend (bool fail_hard = true) = 0;
 
-    // Wait for the machine to terminate up to the specified number of
-    // seconds. Update the timeout and return false if the machine is still
-    // running, true if the machine exited successfully, and throw failed
-    // otherwise.
+    // Wait for the machine to terminate up to the specified number of seconds
+    // (with 0 meaning don't wait). Update the timeout and return false if the
+    // machine is still running, true if the machine exited successfully, and
+    // throw failed otherwise.
     //
     virtual bool
     wait (size_t& seconds, bool fail_hard = true) = 0;
-- 
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