Implemented NamedEvents on Mac using System V semaphores

1 files changed, 95 insertions, 2 deletions

diff --git a/zencore/thread.cpp b/zencore/thread.cpp
index 249eee121..063b060c9 100644
--- a/zencore/thread.cpp
+++ b/zencore/thread.cpp
@@ -30,6 +30,10 @@
 #	include <mqueue.h>
 #endif
 
+#if ZEN_PLATFORM_MAC
+#	include <sys/sem.h>
+#endif
+
 #include <thread>
 
 ZEN_THIRD_PARTY_INCLUDES_START
@@ -292,8 +296,52 @@ NamedEvent::NamedEvent(std::string_view EventName)
 	}
 
 	m_EventHandle = (void*)intptr_t(Inner);
-#else
-#	error Implement NamedEvent for this platform
+#elif ZEN_PLATFORM_MAC
+	// Create a file to back the semaphore
+	ExtendableStringBuilder<64> EventPath;
+	EventPath << "/tmp/" << EventName;
+
+	int Fd = open(EventPath.c_str(), O_RDWR|O_CREAT, 0644);
+	if (Fd < 0)
+	{
+		using namespace fmt::literals;
+		ThrowLastError("Failed to create '{}' for named event"_format(EventPath));
+	}
+
+	// Use the file path to generate an IPC key
+	key_t IpcKey = ftok(EventPath.c_str(), 1);
+	if (IpcKey < 0)
+	{
+		close(Fd);
+		ThrowLastError("Failed to create an SysV IPC key");
+	}
+
+	// Use the key to create/open the semaphore
+	int Sem = semget(IpcKey, 1, 0600 | IPC_CREAT);
+	if (Sem < 0)
+	{
+		close(Fd);
+		ThrowLastError("Failed creating an SysV semaphore");
+	}
+
+	// Atomically claim ownership of the semaphore's key. The owner initialises
+	// the semaphore to 1 so we can use the wait-for-zero op as that does not
+	// modify the semaphore's value on a successful wait.
+	int LockResult = flock(Fd, LOCK_EX | LOCK_NB);
+	if (LockResult == 0)
+	{
+		// This isn't thread safe really. Another thread could open the same
+		// semaphore and successfully wait on it in the period of time where
+		// this comment is but before the semaphore's initialised.
+		semctl(Sem, 0, SETVAL, 1);
+	}
+
+	// Pack into the handle
+	static_assert(sizeof(Sem) + sizeof(Fd) <= sizeof(void*), "Semaphore packing assumptions not met");
+	intptr_t Packed;
+	Packed  = intptr_t(Sem) << 32;
+	Packed |= intptr_t(Fd)  &  0xffff'ffff;
+	m_EventHandle = (void*)Packed;
 #endif
 }
 
@@ -323,6 +371,20 @@ NamedEvent::Close()
 	}
 
 	close(Inner);
+#elif ZEN_PLATFORM_MAC
+	int Fd = int(intptr_t(m_EventHandle) & 0xffff'ffff);
+
+	if (flock(Fd, LOCK_EX | LOCK_NB) == 0)
+	{
+		std::filesystem::path Name = PathFromHandle((void*)(intptr_t(Fd)));
+		unlink(Name.c_str());
+
+		flock(Fd, LOCK_UN | LOCK_NB);
+		close(Fd);
+
+		int Sem = int(intptr_t(m_EventHandle) >> 32);
+		semctl(Sem, 0, IPC_RMID);
+	}
 #endif
 
 	m_EventHandle = nullptr;
@@ -346,6 +408,9 @@ NamedEvent::Set()
 	{
 		ThrowLastError("Unable to send set message to queue");
 	}
+#elif ZEN_PLATFORM_MAC
+	int Sem = int(intptr_t(m_EventHandle) >> 32);
+	semctl(Sem, 0, SETVAL, 0);
 #endif
 }
 
@@ -382,6 +447,34 @@ NamedEvent::Wait(int TimeoutMs)
 	FD_ZERO(&FdSet);
 	FD_SET(Inner, &FdSet);
 	return select(Inner + 1, &FdSet, nullptr, nullptr, TimeoutPtr) > 0;
+#elif ZEN_PLATFORM_MAC
+	int Sem = int(intptr_t(m_EventHandle) >> 32);
+
+	int Result;
+	struct sembuf SemOp = {};
+
+	if (TimeoutMs < 0)
+	{
+		Result = semop(Sem, &SemOp, 1);
+		return Result == 0;
+	}
+
+	const int SleepTimeMs = 10;
+	SemOp.sem_flg = IPC_NOWAIT;
+	do
+	{
+		Result = semop(Sem, &SemOp, 1);
+		if (Result == 0 || errno != EAGAIN)
+		{
+			break;
+		}
+
+		Sleep(SleepTimeMs);
+		TimeoutMs -= SleepTimeMs;
+	}
+	while (TimeoutMs > 0);
+
+	return Result == 0;
 #endif
 }