Allow multiple messages to be scheduled with the same ID if the interval is set to 0

README.md

@@ -37,7 +37,8 @@ new call with different data is sent before the previous
 interval is up. Sending a frame with an interval of -1
 will cancel the repeat, and not send the frame. Sending with
 an interval of 0 will schedule the new frame once, then stop
-repeating.
+repeating. Unlike with a positive interval, an interval of 0 
+guarantees that each new message will be sent.
 
 ## Build Requirements
 

src/main/native/include/rev/Drivers/DriverDeviceThread.h

@@ -75,9 +75,9 @@ class DriverDeviceThread {
         }
     }
 
-    detail::CANThreadSendQueueElement* findFirstMatchingId(int targetId) {
+    detail::CANThreadSendQueueElement* findFirstMatchingIdWithNonZeroInterval(int targetId) {
         for (auto& element : m_sendQueue) {
-            if (element.m_msg.GetMessageId() == targetId) {
+            if (element.m_msg.GetMessageId() == targetId && element.m_intervalMs > 0) {
                 return &element;
             }
         }
@@ -91,13 +91,25 @@ class DriverDeviceThread {
     bool EnqueueMessage(const CANMessage& msg, int32_t timeIntervalMs) {
         std::lock_guard<std::mutex> lock(m_writeMutex);
 
-        detail::CANThreadSendQueueElement* existing = findFirstMatchingId(msg.GetMessageId());
+        if(timeIntervalMs == 0) {
+            // If the time interval is 0, we want to allow duplicates.
+            m_sendQueue.push_back(detail::CANThreadSendQueueElement(msg, timeIntervalMs));
 
-        if(existing) {
-            existing->m_intervalMs = timeIntervalMs;
-            existing->m_msg = msg;
+            // Cancel existing repeating frame with same id
+            detail::CANThreadSendQueueElement* existing = findFirstMatchingIdWithNonZeroInterval(msg.GetMessageId());
+            if(existing) {
+                existing->m_intervalMs = -1;
+            }
         } else {
-            m_sendQueue.push_back(detail::CANThreadSendQueueElement(msg, timeIntervalMs));
+            // We don't want to replace elements with zero as the interval. Those should be guaranteed to be sent
+            detail::CANThreadSendQueueElement* existing = findFirstMatchingIdWithNonZeroInterval(msg.GetMessageId());
+
+            if(existing) {
+                existing->m_intervalMs = timeIntervalMs;
+                existing->m_msg = msg;
+            } else {
+                m_sendQueue.push_back(detail::CANThreadSendQueueElement(msg, timeIntervalMs));
+            }
         }
 
         // TODO: Limit the max queue size