From 389305ded99e9c6dc0827584d6e997151fb25cb6 Mon Sep 17 00:00:00 2001
From: Martin Ridgers <martin.ridgers@epicgames.com>
Date: Thu, 25 Nov 2021 14:31:44 +0100
Subject: Use file descriptor locks to claim global ownership of message queues

---
 zencore/thread.cpp | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

(limited to 'zencore/thread.cpp')

diff --git a/zencore/thread.cpp b/zencore/thread.cpp
index e009ccc41..3eeecbf4c 100644
--- a/zencore/thread.cpp
+++ b/zencore/thread.cpp
@@ -3,6 +3,7 @@
 #include <zencore/thread.h>
 
 #include <zencore/except.h>
+#include <zencore/filesystem.h>
 #include <zencore/scopeguard.h>
 #include <zencore/string.h>
 #include <zencore/testing.h>
@@ -20,6 +21,7 @@
 #	include <mqueue.h>
 #	include <pthread.h>
 #	include <signal.h>
+#	include <sys/file.h>
 #	include <time.h>
 #	include <unistd.h>
 #endif
@@ -267,13 +269,18 @@ NamedEvent::NamedEvent(std::string_view EventName)
 		0, // current messages
 	};
 
-    int Inner = mq_open(Name.c_str(), O_RDWR|O_CREAT|O_CLOEXEC, 0666, &Attributes);
+	int Inner = mq_open(Name.c_str(), O_RDWR|O_CREAT|O_CLOEXEC, 0644, &Attributes);
 	if (Inner < 0)
 	{
 		ThrowLastError("Failed to get message queue from mq_open()");
 	}
 
-	//mq_unlink(Name.c_str());
+	int LockResult = flock(Inner, LOCK_EX|LOCK_NB);
+	if (LockResult == 0)
+	{
+		ZEN_ASSERT( IsThereAMessageInQueue(Inner) == false,
+					"Ownership of a non-empty '{}' message queue occurred", Name.c_str());
+	}
 
 	m_EventHandle = (void*)intptr_t(Inner);
 #else
@@ -297,6 +304,14 @@ void NamedEvent::Close()
 	CloseHandle(m_EventHandle);
 #elif ZEN_PLATFORM_LINUX
 	int Inner = int(intptr_t(m_EventHandle));
+
+	if (flock(Inner, LOCK_EX|LOCK_NB) == 0)
+	{
+		flock(Inner, LOCK_UN|LOCK_NB);
+		std::filesystem::path Name = PathFromHandle((void*)(intptr_t(Inner)));
+		mq_unlink(Name.c_str());
+	}
+
 	close(Inner);
 #endif
 
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