harden attach sponsor process (#14)

- Improvement: Delay exiting due to no sponsor processes by one second to handle race conditions
- Improvement: Safer IsProcessRunning check
- Improvement: make sure we can RequestApplicationExit safely from any thread

1 files changed, 31 insertions, 14 deletions

diff --git a/src/zenserver/zenserver.cpp b/src/zenserver/zenserver.cpp
index daec743a0..d1faeb8b6 100644
--- a/src/zenserver/zenserver.cpp
+++ b/src/zenserver/zenserver.cpp
@@ -693,7 +693,6 @@ ZenServer::Run()
 	if (m_IsPowerCycle)
 	{
 		ZEN_INFO("Power cycle mode enabled -- shutting down");
-
 		RequestExit(0);
 	}
 
@@ -707,10 +706,12 @@ ZenServer::Run()
 void
 ZenServer::RequestExit(int ExitCode)
 {
-	RequestApplicationExit(ExitCode);
-	if (m_Http)
+	if (RequestApplicationExit(ExitCode))
 	{
-		m_Http->RequestExit();
+		if (m_Http)
+		{
+			m_Http->RequestExit();
+		}
 	}
 }
 
@@ -779,7 +780,7 @@ ZenServer::EnsureIoRunner()
 }
 
 void
-ZenServer::EnqueueTimer()
+ZenServer::EnqueueProcessMonitorTimer()
 {
 	m_PidCheckTimer.expires_after(std::chrono::seconds(1));
 	m_PidCheckTimer.async_wait([this](const asio::error_code&) { CheckOwnerPid(); });
@@ -857,11 +858,10 @@ ZenServer::CheckSigInt()
 	EnqueueSigIntTimer();
 }
 
-void
-ZenServer::CheckOwnerPid()
+bool
+ZenServer::UpdateProcessMonitor()
 {
 	// Pick up any new "owner" processes
-
 	std::set<uint32_t> AddedPids;
 
 	for (auto& PidEntry : m_ServerEntry->SponsorPids)
@@ -874,21 +874,38 @@ ZenServer::CheckOwnerPid()
 				{
 					m_ProcessMonitor.AddPid(ThisPid);
 
-					ZEN_INFO("added process with pid #{} as a sponsor process", ThisPid);
+					ZEN_INFO("added process with pid {} as a sponsor process", ThisPid);
 				}
 			}
 		}
 	}
+	return m_ProcessMonitor.IsRunning();
+}
 
-	if (m_ProcessMonitor.IsRunning())
+void
+ZenServer::CheckOwnerPid()
+{
+	bool IsRunning = UpdateProcessMonitor();
+
+	if (IsRunning)
 	{
-		EnqueueTimer();
+		m_FoundNoActiveSponsors = false;
+		EnqueueProcessMonitorTimer();
 	}
 	else
 	{
-		ZEN_INFO(ZEN_APP_NAME " exiting since sponsor processes are all gone");
-
-		RequestExit(0);
+		// Delay exit one iteration to avoid race conditions where one process detaches
+		// and another attaches
+		if (m_FoundNoActiveSponsors)
+		{
+			ZEN_INFO(ZEN_APP_NAME " exiting since sponsor processes are all gone");
+			RequestExit(0);
+		}
+		else
+		{
+			m_FoundNoActiveSponsors = true;
+			EnqueueProcessMonitorTimer();
+		}
 	}
 }