Add support for low latency mode

X-Ryl669 · Mar 28, 2024 · 986a7f8 · 986a7f8
1 parent 5d45929
commit 986a7f8
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Showing 4 changed files with 41 additions and 11 deletions.
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -12,6 +12,7 @@ project(eMQTT5)
 option(REDUCED_FOOTPRINT "Whether to enable reduced footprint for the client code" ON)
 option(CROSSPLATFORM_SOCKET "Whether to use cross plaftform socket code (this disable SSL)" OFF)
 option(ENABLE_TLS "Whether to enable TLS/SSL code (you'll need MBedTLS available)" OFF)
+option(LOW_LATENCY "Whether to enable low latency code (at the cost of higher CPU usage)" OFF)
 
 if (CROSSPLATFORM_SOCKET STREQUAL OFF AND ENABLE_TLS STREQUAL ON)
    message(WARNING "As of 06/28/2020, MBedTLS is not correctly CMake compatible and does not generate a mbedtls-config.cmake file. You'll need to apply the patch from my branch found in pull request #3465")  

diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
@@ -20,7 +20,8 @@ ENDIF()
 target_compile_definitions(eMQTT5 PUBLIC _DEBUG=$<CONFIG:Debug> 
                                         MinimalFootPrint=$<STREQUAL:${REDUCED_FOOTPRINT},ON>
                                         MQTTOnlyBSDSocket=$<STREQUAL:${CROSSPLATFORM_SOCKET},OFF> 
-                                        MQTTUseTLS=$<AND:$<STREQUAL:${CROSSPLATFORM_SOCKET},OFF>,$<STREQUAL:${ENABLE_TLS},ON>>)
+                                        MQTTUseTLS=$<AND:$<STREQUAL:${CROSSPLATFORM_SOCKET},OFF>,$<STREQUAL:${ENABLE_TLS},ON>>
+					MQTTLowLatency=$<STREQUAL:${LOW_LATENCY},ON>)
 
 IF (WIN32)
 ELSE()

diff --git a/lib/include/Network/Clients/MQTTConfig.hpp b/lib/include/Network/Clients/MQTTConfig.hpp
@@ -62,6 +62,19 @@
   #define MQTTOnlyBSDSocket   1
 #endif
 
+/** Low latency mode
+    If set to 1, this will only wait on the receiving socket in a non blocking fashion.
+    You'll use this if you need to do other processing in your main application loop. It reduces latency for your
+    other application code at the cost of increased CPU usage since the loop time will decrease from the default
+    timeout set to mainly the duration of a system call.
+
+    This allow implies you provide a BSD compatible select function for the socket implementation.
+
+    Default: 0 */
+#ifndef MQTTLowLatency
+  #define MQTTLowLatency  0
+#endif
+
 // The part below is for building only, it's made to generate a message so the configuration is visible at build time
 #if _DEBUG == 1
   #if MQTTUseAuth == 1
@@ -95,13 +108,21 @@
     #define CONF_TLS "_"
   #endif
 
+  #if MQTTLowLatency == 1
+    #define CONF_LL "LL_"
+  #else
+    #define CONF_LL "_"
+  #endif
+
   #if MQTTOnlyBSDSocket == 1
     #define CONF_SOCKET "BSD"
   #else
     #define CONF_SOCKET "CP"
   #endif
 
-  #pragma message("Building eMQTT5 with flags: " CONF_AUTH CONF_UNSUB CONF_DUMP CONF_VALID CONF_TLS CONF_SOCKET)
+
+
+  #pragma message("Building eMQTT5 with flags: " CONF_AUTH CONF_UNSUB CONF_DUMP CONF_VALID CONF_TLS CONF_LL CONF_SOCKET)
 #endif
 
 #endif
diff --git a/lib/src/Network/Clients/MQTTClient.cpp b/lib/src/Network/Clients/MQTTClient.cpp
@@ -175,7 +175,7 @@ namespace Network { namespace Client {
             @retval 0           Protocol error, you should close the socket
             @retval -1          Socket error
             @retval -2          Timeout */
-        int receiveControlPacket()
+        int receiveControlPacket(const bool lowLatency = false)
         {
             if (!socket) return -1;
             // Depending on the current state, we need to fetch as many bytes as possible within the given timeoutMs
@@ -192,6 +192,11 @@ namespace Network { namespace Client {
             int ret = 0;
             Protocol::MQTT::Common::VBInt len;
 
+#if MQTTLowLatency == 1
+            // In low latency mode, return as early as possible
+            if (lowLatency && !socket->select(true, false, 0)) return -2;
+#endif
+
             // We want to keep track of complete timeout time over multiple operations
             Time::TimeOut timeout(timeoutMs);
             switch (recvState)
@@ -618,15 +623,12 @@ namespace Network { namespace Client {
         }
 
         // Useful socket helpers functions here
-        MQTTVirtual int select(bool reading, bool writing)
+        MQTTVirtual int select(bool reading, bool writing, bool instantaneous = false)
         {
-#if (_LINUX == 1)
             // Linux modifies the timeout when calling select
             struct timeval v = timeoutMs;
-#else
-            // Other system don't
-            struct timeval & v = timeoutMs;
-#endif
+            if (instantaneous) memset(&v, 0, sizeof(v));
+
             fd_set set;
             FD_ZERO(&set);
             FD_SET(socket, &set);
@@ -866,7 +868,7 @@ namespace Network { namespace Client {
             @retval 0           Protocol error, you should close the socket
             @retval -1          Socket error
             @retval -2          Timeout */
-        int receiveControlPacket()
+        int receiveControlPacket(const bool lowLatency = false)
         {
             if (!socket) return -1;
             // Depending on the current state, we need to fetch as many bytes as possible within the given timeoutMs
@@ -883,6 +885,11 @@ namespace Network { namespace Client {
             int ret = 0;
             Protocol::MQTT::Common::VBInt len;
 
+#if MQTTLowLatency == 1
+            // In low latency mode, return as early as possible
+            if (lowLatency && !socket->select(true, false, true)) return -2;
+#endif
+
             // We want to keep track of complete timeout time over multiple operations
             switch (recvState)
             {
@@ -1551,7 +1558,7 @@ namespace Network { namespace Client {
                     return ret;
             }
             // Check the server for any packet...
-            int ret = impl->receiveControlPacket();
+            int ret = impl->receiveControlPacket(true);
             if (ret == 0)
             {
                 impl->close();