From 61c370dfb7b98de2e4f29825a39bf7dba953434c Mon Sep 17 00:00:00 2001
From: Stefan Boberg <stefan@boberg.org>
Date: Thu, 5 Aug 2021 21:38:25 +0200
Subject: Added single instance (per port) logic to ZenServer class

---
 zenserver/zenserver.cpp | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/zenserver/zenserver.cpp b/zenserver/zenserver.cpp
index c55d3497e..646b6cf5c 100644
--- a/zenserver/zenserver.cpp
+++ b/zenserver/zenserver.cpp
@@ -12,6 +12,7 @@
 #include <zenstore/cas.h>
 #include <zenstore/cidstore.h>
 
+#include <exception>
 #include <fmt/format.h>
 #include <mimalloc-new-delete.h>
 #include <mimalloc.h>
@@ -78,6 +79,15 @@ public:
 			}
 		}
 
+		// Initialize/check mutex based on base port
+
+		std::string MutexName = "zen_{}"_format(BasePort);
+
+		if (zen::NamedMutex::Exists(MutexName) || (m_ServerMutex.Create(MutexName) == false))
+		{
+			throw std::exception("Failed to create mutex '{}' - is another instance already running?"_format(MutexName).c_str());
+		}
+
 		// Ok so now we're configured, let's kick things off
 
 		zen::CasStoreConfiguration Config;
@@ -231,6 +241,7 @@ private:
 	asio::io_context	  m_IoContext;
 	asio::steady_timer	  m_PidCheckTimer{m_IoContext};
 	zen::Process		  m_Process;
+	zen::NamedMutex		  m_ServerMutex;
 
 	zen::HttpServer									 m_Http;
 	std::unique_ptr<zen::CasStore>					 m_CasStore{zen::CreateCasStore()};
@@ -277,6 +288,9 @@ main(int argc, char* argv[])
 		Server.SetTestMode(GlobalOptions.IsTest);
 		Server.Initialize(ServiceConfig, GlobalOptions.BasePort, GlobalOptions.OwnerPid);
 
+		// If we have a parent process, establish the mechanisms we need
+		// to be able to communicate with the parent
+
 		if (!GlobalOptions.ChildId.empty())
 		{
 			zen::ExtendableStringBuilder<64> ShutdownEventName;
@@ -287,6 +301,7 @@ main(int argc, char* argv[])
 			ParentEvent.Set();
 
 			ShutdownThread.reset(new std::thread{[&] {
+				spdlog::info("shutdown monitor thread waiting for shutdown signal '{}'", ShutdownEventName);
 				ShutdownEvent->Wait();
 				spdlog::info("shutdown signal received");
 				Server.RequestExit(0);
-- 
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