From d4d73addfeafbc1869d8a0252885483af2d9c7a8 Mon Sep 17 00:00:00 2001
From: Martin Ridgers <martin.ridgers@epicgames.com>
Date: Thu, 11 Nov 2021 14:17:18 +0100
Subject: Implement NamedEvent on POSIX using Unix-domain sockets

---
 zencore/thread.cpp | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 80 insertions(+), 3 deletions(-)

(limited to 'zencore/thread.cpp')

diff --git a/zencore/thread.cpp b/zencore/thread.cpp
index df8b0301f..0b9534c39 100644
--- a/zencore/thread.cpp
+++ b/zencore/thread.cpp
@@ -13,8 +13,11 @@
 #	include <condition_variable>
 #	include <mutex>
 
+#	include <poll.h>
 #	include <pthread.h>
 #	include <signal.h>
+#	include <sys/socket.h>
+#	include <sys/un.h>
 #	include <time.h>
 #	include <unistd.h>
 #endif
@@ -226,10 +229,18 @@ Event::Wait(int TimeoutMs)
 
 //////////////////////////////////////////////////////////////////////////
 
-#if ZEN_PLATFORM_WINDOWS
+#if ZEN_PLATFORM_LINUX || ZEN_PLATFORM_MACOS
+struct NamedEventPosix
+{
+	int			SocketFd	= 0;
+	sockaddr_un	SocketAddr	= {};
+	bool		bBound		= false;
+};
+#endif
 
 NamedEvent::NamedEvent(std::string_view EventName)
 {
+#if ZEN_PLATFORM_WINDOWS
 	using namespace std::literals;
 
 	ExtendableStringBuilder<64> Name;
@@ -237,6 +248,27 @@ NamedEvent::NamedEvent(std::string_view EventName)
 	Name << EventName;
 
 	m_EventHandle = CreateEventA(nullptr, true, false, Name.c_str());
+#else
+    int SocketFd = socket(AF_UNIX, SOCK_DGRAM, SOCK_CLOEXEC);
+	if (SocketFd < 0)
+	{
+		ThrowLastError("Failed to create IPC socket");
+	}
+
+	auto* Inner = new NamedEventPosix();
+	Inner->SocketFd = SocketFd;
+
+    char* PathPtr = Inner->SocketAddr.sun_path;
+    size_t PathLen = sizeof(Inner->SocketAddr.sun_path) - 1; // -1 for null-term
+#	if ZEN_PLATFORM_LINUX
+    PathPtr[0] = '\0';  // make the domain socket...
+    PathPtr += 1;       // ...use the abstract namespace
+	PathLen -= 1;
+#	endif
+	EventName.copy(PathPtr, PathLen);
+#endif
+
+	m_EventHandle = Inner;
 }
 
 NamedEvent::~NamedEvent()
@@ -251,18 +283,37 @@ void NamedEvent::Close()
 		return;
 	}
 
+#if ZEN_PLATFORM_WINDOWS
 	CloseHandle(m_EventHandle);
+#else
+	auto* Inner = (NamedEventPosix*)m_EventHandle;
+	close(Inner->SocketFd);
+	delete Inner;
+#endif
 
 	m_EventHandle = nullptr;
 }
 
+
 void NamedEvent::Set()
 {
+#if ZEN_PLATFORM_WINDOWS
 	SetEvent(m_EventHandle);
+#else
+	auto* Inner = (NamedEventPosix*)m_EventHandle;
+
+	uint8_t OneByte = 0x49;
+	sendto(
+		Inner->SocketFd,
+		&OneByte, sizeof(OneByte),
+		0, (sockaddr*)&Inner->SocketAddr, sizeof(Inner->SocketAddr)
+	);
+#endif
 }
 
 bool NamedEvent::Wait(int TimeoutMs)
 {
+#if ZEN_PLATFORM_WINDOWS
 	const DWORD Timeout = (TimeoutMs < 0) ? INFINITE : TimeoutMs;
 
 	DWORD Result = WaitForSingleObject(m_EventHandle, Timeout);
@@ -274,9 +325,35 @@ bool NamedEvent::Wait(int TimeoutMs)
 	}
 
 	return (Result == WAIT_OBJECT_0);
-}
+#else
+	auto* Inner = (NamedEventPosix*)m_EventHandle;
+	int SocketFd = Inner->SocketFd;
 
-#endif // ZEN_PLATFORM_WINDOWS
+	int Result;
+
+	if (!Inner->bBound)
+	{
+		Result = bind(SocketFd, (sockaddr*)&(Inner->SocketAddr), sizeof(Inner->SocketAddr));
+		if (!Result)
+		{
+			zen::ThrowLastError("Bind IPC socket failed");
+		}
+		Inner->bBound = true;
+	}
+
+	pollfd PollFd = { SocketFd, POLLIN };
+	Result = poll(&PollFd, 1, TimeoutMs);
+	if (Result > 0)
+	{
+		uint8_t OneByte;
+		Result = recv(SocketFd, &OneByte, sizeof(OneByte), 0);
+
+		return true;
+	}
+
+	return false;
+#endif
+}
 
 //////////////////////////////////////////////////////////////////////////
 
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