Core/Process: Add Exists function

src/Nazara/Core/Win32/ProcessImpl.cpp

@@ -6,6 +6,7 @@
 #include <Nazara/Core/Error.hpp>
 #include <Nazara/Core/StringExt.hpp>
 #include <Nazara/Core/Win32/Win32Utils.hpp>
+#include <NazaraUtils/CallOnExit.hpp>
 #include <Windows.h>
 #include <Nazara/Core/Debug.hpp>
 
@@ -85,6 +86,27 @@ namespace Nz::PlatformImpl
 		return commandLine;
 	}
 
+	Result<bool, std::string> CheckProcessExistence(Pid pid)
+	{
+		HANDLE processHandle = ::OpenProcess(PROCESS_QUERY_LIMITED_INFORMATION, FALSE, pid);
+		if (!processHandle)
+		{
+			DWORD lastErr = ::GetLastError();
+			if (lastErr == ERROR_INVALID_PARAMETER)
+				return Ok(false);
+
+			return Err("failed to open process handle: " + Error::GetLastSystemError());
+		}
+		CallOnExit releaseHandle([processHandle] { ::CloseHandle(processHandle); });
+
+		// Opening a handle doesn't mean the process hasn't exited (zombie processes), check if it has an exit code
+		DWORD exitCode;
+		if (!::GetExitCodeProcess(processHandle, &exitCode))
+			return Err("failed to get exit code: " + Error::GetLastSystemError());
+
+		return Ok(exitCode == STILL_ACTIVE);
+	}
+
 	Pid GetCurrentProcessId()
 	{
 		return ::GetCurrentProcessId();

src/Nazara/Core/Win32/ProcessImpl.hpp

@@ -12,6 +12,7 @@
 
 namespace Nz::PlatformImpl
 {
+	Result<bool, std::string> CheckProcessExistence(Pid pid);
 	Pid GetCurrentProcessId();
 	Result<Pid, std::string> SpawnDetachedProcess(const std::filesystem::path& program, std::span<const std::string> arguments = {}, const std::filesystem::path& workingDirectory = {});
 }