From 581675818b32d660bed6933102632e9f63292fde Mon Sep 17 00:00:00 2001
From: Norman Princen <nprincen@hotmail.com>
Date: Tue, 12 May 2020 09:57:38 -0700
Subject: [PATCH] Minimize sendUDP and readUDP Socket Timeout Delays

sendUDP and readUDP were using longer than necessary socket timeouts that may add to process time delay and stuttering.  They were also using different values between Window and Linux/Mac.  The timeouts are now standardized for all versions.
---
 C/src/xplaneConnect.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/C/src/xplaneConnect.c b/C/src/xplaneConnect.c
index d48ac02..11cc6a8 100755
--- a/C/src/xplaneConnect.c
+++ b/C/src/xplaneConnect.c
@@ -117,13 +117,16 @@ XPCSocket aopenUDP(const char *xpIP, unsigned short xpPort, unsigned short port)
 		exit(EXIT_FAILURE);
 	}
 
-	// Set timeout to 100ms
+	// Set socket timeout period for sendUDP to 1 millisecond
+	// Without this, playback may become choppy due to process blocking
 #ifdef _WIN32
-	DWORD timeout = 100;
+	// Minimum socket timeout in Windows is 1 millisecond (0 makes it blocking)
+	DWORD timeout = 1;
 #else
+	// Set socket timeout to 1 millisecond = 1,000 microseconds to make it the same as Windows (0 makes it blocking)
 	struct timeval timeout;
 	timeout.tv_sec = 0;
-	timeout.tv_usec = 250000;
+	timeout.tv_usec = 1000;
 #endif
 	if (setsockopt(sock.sock, SOL_SOCKET, SO_RCVTIMEO, (char*)&timeout, sizeof(timeout)) < 0)
 	{
@@ -188,13 +191,13 @@ int sendUDP(XPCSocket sock, char buffer[], int len)
 /// \returns      If an error occurs, a negative number. Otherwise, the number of bytes read.
 int readUDP(XPCSocket sock, char buffer[], int len)
 {
-#ifdef _WIN32
-	// Windows readUDP needs the select command- minimum timeout is 1ms.
-	// Without this playback becomes choppy
+	// For readUDP, use the select command - minimum timeout of 0 makes it polling.
+	// Without this, playback may become choppy due to process blocking
 
 	// Definitions
 	FD_SET stReadFDS;
 	FD_SET stExceptFDS;
+	struct timeval tv;
 
 	// Setup for Select
 	FD_ZERO(&stReadFDS);
@@ -202,9 +205,10 @@ int readUDP(XPCSocket sock, char buffer[], int len)
 	FD_ZERO(&stExceptFDS);
 	FD_SET(sock.sock, &stExceptFDS);
 
-	struct timeval tv;
+	// Set timeout period for select to 0.05 sec = 50 milliseconds = 50,000 microseconds (0 makes it polling)
+	// TO DO - This could be set to 0 if a message handling system were implemented, like in the plugin.
 	tv.tv_sec = 0;
-	tv.tv_usec = 100000;
+	tv.tv_usec = 50000;
 
 	// Select Command
 	int status = select(-1, &stReadFDS, (FD_SET*)0, &stExceptFDS, &tv);
@@ -218,11 +222,9 @@ int readUDP(XPCSocket sock, char buffer[], int len)
 		// No data
 		return 0;
 	}
+
+	// If no error: Read Data
 	status = recv(sock.sock, buffer, len, 0);
-#else
-	// For apple or linux-just read - will timeout in 0.5 ms
-	int status = (int)recv(sock.sock, buffer, len, 0);
-#endif
 	if (status < 0)
 	{
 		printError("readUDP", "Error reading socket");