Merge pull request #33 from mathieucarbou/coalescedq

Coalesce poll events on queue eviction

src/AsyncTCP.cpp

@@ -61,6 +61,12 @@ extern "C" {
 
 #define INVALID_CLOSED_SLOT -1
 
+/*
+  TCP poll interval is specified in terms of the TCP coarse timer interval, which is called twice a second
+  https://github.com/espressif/esp-lwip/blob/2acf959a2bb559313cd2bf9306c24612ba3d0e19/src/core/tcp.c#L1895
+*/
+#define CONFIG_ASYNC_TCP_POLL_TIMER 1
+
 /*
  * TCP/IP Event Task
  * */
@@ -139,16 +145,67 @@ static inline bool _init_async_event_queue() {
   return true;
 }
 
-static inline bool _send_async_event(lwip_event_packet_t** e) {
-  return _async_queue && xQueueSend(_async_queue, e, portMAX_DELAY) == pdPASS;
+static inline bool _send_async_event(lwip_event_packet_t** e, TickType_t wait = portMAX_DELAY) {
+  return _async_queue && xQueueSend(_async_queue, e, wait) == pdPASS;
 }
 
-static inline bool _prepend_async_event(lwip_event_packet_t** e) {
-  return _async_queue && xQueueSendToFront(_async_queue, e, portMAX_DELAY) == pdPASS;
+static inline bool _prepend_async_event(lwip_event_packet_t** e, TickType_t wait = portMAX_DELAY) {
+  return _async_queue && xQueueSendToFront(_async_queue, e, wait) == pdPASS;
 }
 
 static inline bool _get_async_event(lwip_event_packet_t** e) {
-  return _async_queue && xQueueReceive(_async_queue, e, portMAX_DELAY) == pdPASS;
+  if (!_async_queue) {
+    return false;
+  }
+
+#if CONFIG_ASYNC_TCP_USE_WDT
+  // need to return periodically to feed the dog
+  if (xQueueReceive(_async_queue, e, pdMS_TO_TICKS(1000)) != pdPASS)
+    return false;
+#else
+  if (xQueueReceive(_async_queue, e, portMAX_DELAY) != pdPASS)
+    return false;
+#endif
+
+  if ((*e)->event != LWIP_TCP_POLL)
+    return true;
+
+  /*
+    Let's try to coalesce two (or more) consecutive poll events into one
+    this usually happens with poor implemented user-callbacks that are runs too long and makes poll events to stack in the queue
+    if consecutive user callback for a same connection runs longer that poll time then it will fill the queue with events until it deadlocks.
+    This is a workaround to mitigate such poor designs and won't let other events/connections to starve the task time.
+    It won't be effective if user would run multiple simultaneous long running callbacks due to message interleaving.
+    todo: implement some kind of fair dequeing or (better) simply punish user for a bad designed callbacks by resetting hog connections
+  */
+  lwip_event_packet_t* next_pkt = NULL;
+  while (xQueuePeek(_async_queue, &next_pkt, 0) == pdPASS) {
+    if (next_pkt->arg == (*e)->arg && next_pkt->event == LWIP_TCP_POLL) {
+      if (xQueueReceive(_async_queue, &next_pkt, 0) == pdPASS) {
+        free(next_pkt);
+        next_pkt = NULL;
+        log_d("coalescing polls, network congestion or async callbacks might be too slow!");
+        continue;
+      }
+    } else {
+      /*
+        poor designed apps using asynctcp without proper dataflow control could flood the queue with interleaved pool/ack events.
+        We can try to mitigate it by discarding poll events when queue grows too much.
+        Let's discard poll events using linear probability curve starting from 3/4 of queue length
+        Poll events are periodic and connection could get another chance next time
+      */
+      if (uxQueueMessagesWaiting(_async_queue) > (rand() % CONFIG_ASYNC_TCP_QUEUE_SIZE / 4 + CONFIG_ASYNC_TCP_QUEUE_SIZE * 3 / 4)) {
+        free(next_pkt);
+        next_pkt = NULL;
+        log_d("discarding poll due to queue congestion");
+        // evict next event from a queue
+        return _get_async_event(e);
+      }
+    }
+    return true;
+  }
+  // last resort return
+  return true;
 }
 
 static bool _remove_events_with_arg(void* arg) {
@@ -167,8 +224,11 @@ static bool _remove_events_with_arg(void* arg) {
     if ((int)first_packet->arg == (int)arg) {
       free(first_packet);
       first_packet = NULL;
-      // return first packet to the back of the queue
-    } else if (xQueueSend(_async_queue, &first_packet, portMAX_DELAY) != pdPASS) {
+
+      // try to return first packet to the back of the queue
+    } else if (xQueueSend(_async_queue, &first_packet, 0) != pdPASS) {
+      // we can't wait here if queue is full, because this call has been done from the only consumer task of this queue
+      // otherwise it would deadlock, we have to discard the event
       return false;
     }
   }
@@ -180,7 +240,9 @@ static bool _remove_events_with_arg(void* arg) {
     if ((int)packet->arg == (int)arg) {
       free(packet);
       packet = NULL;
-    } else if (xQueueSend(_async_queue, &packet, portMAX_DELAY) != pdPASS) {
+    } else if (xQueueSend(_async_queue, &packet, 0) != pdPASS) {
+      // we can't wait here if queue is full, because this call has been done from the only consumer task of this queue
+      // otherwise it would deadlock, we have to discard the event
       return false;
     }
   }
@@ -222,22 +284,23 @@ static void _handle_async_event(lwip_event_packet_t* e) {
 }
 
 static void _async_service_task(void* pvParameters) {
+#if CONFIG_ASYNC_TCP_USE_WDT
+  if (esp_task_wdt_add(NULL) != ESP_OK) {
+    log_w("Failed to add async task to WDT");
+  }
+#endif
   lwip_event_packet_t* packet = NULL;
   for (;;) {
     if (_get_async_event(&packet)) {
-#if CONFIG_ASYNC_TCP_USE_WDT
-      if (esp_task_wdt_add(NULL) != ESP_OK) {
-        log_e("Failed to add async task to WDT");
-      }
-#endif
       _handle_async_event(packet);
-#if CONFIG_ASYNC_TCP_USE_WDT
-      if (esp_task_wdt_delete(NULL) != ESP_OK) {
-        log_e("Failed to remove loop task from WDT");
     }
+#if CONFIG_ASYNC_TCP_USE_WDT
+    esp_task_wdt_reset();
 #endif
   }
-  }
+#if CONFIG_ASYNC_TCP_USE_WDT
+  esp_task_wdt_delete(NULL);
+#endif
   vTaskDelete(NULL);
   _async_service_task_handle = NULL;
 }
@@ -311,6 +374,7 @@ static int8_t _tcp_connected(void* arg, tcp_pcb* pcb, int8_t err) {
 
 static int8_t _tcp_poll(void* arg, struct tcp_pcb* pcb) {
   // throttle polling events queing when event queue is getting filled up, let it handle _onack's
+  // log_d("qs:%u", uxQueueMessagesWaiting(_async_queue));
   if (uxQueueMessagesWaiting(_async_queue) > (rand() % CONFIG_ASYNC_TCP_QUEUE_SIZE / 2 + CONFIG_ASYNC_TCP_QUEUE_SIZE / 4)) {
     log_d("throttling");
     return ERR_OK;
@@ -321,7 +385,8 @@ static int8_t _tcp_poll(void* arg, struct tcp_pcb* pcb) {
   e->event = LWIP_TCP_POLL;
   e->arg = arg;
   e->poll.pcb = pcb;
-  if (!_send_async_event(&e)) {
+  // poll events are not critical 'cause those are repetitive, so we may not wait the queue in any case
+  if (!_send_async_event(&e, 0)) {
     free((void*)(e));
   }
   return ERR_OK;
@@ -612,7 +677,7 @@ AsyncClient::AsyncClient(tcp_pcb* pcb)
     tcp_recv(_pcb, &_tcp_recv);
     tcp_sent(_pcb, &_tcp_sent);
     tcp_err(_pcb, &_tcp_error);
-    tcp_poll(_pcb, &_tcp_poll, 1);
+    tcp_poll(_pcb, &_tcp_poll, CONFIG_ASYNC_TCP_POLL_TIMER);
     if (!_allocate_closed_slot()) {
       _close();
     }
@@ -643,7 +708,7 @@ AsyncClient& AsyncClient::operator=(const AsyncClient& other) {
     tcp_recv(_pcb, &_tcp_recv);
     tcp_sent(_pcb, &_tcp_sent);
     tcp_err(_pcb, &_tcp_error);
-    tcp_poll(_pcb, &_tcp_poll, 1);
+    tcp_poll(_pcb, &_tcp_poll, CONFIG_ASYNC_TCP_POLL_TIMER);
   }
   return *this;
 }
@@ -741,7 +806,7 @@ bool AsyncClient::_connect(ip_addr_t addr, uint16_t port) {
   tcp_err(pcb, &_tcp_error);
   tcp_recv(pcb, &_tcp_recv);
   tcp_sent(pcb, &_tcp_sent);
-  tcp_poll(pcb, &_tcp_poll, 1);
+  tcp_poll(pcb, &_tcp_poll, CONFIG_ASYNC_TCP_POLL_TIMER);
   TCP_MUTEX_UNLOCK();
 
   esp_err_t err = _tcp_connect(pcb, _closed_slot, &addr, port, (tcp_connected_fn)&_tcp_connected);
@@ -1090,10 +1155,6 @@ void AsyncClient::_dns_found(struct ip_addr* ipaddr) {
  * Public Helper Methods
  * */
 
-void AsyncClient::stop() {
-  close(false);
-}
-
 bool AsyncClient::free() {
   if (!_pcb) {
     return true;
@@ -1104,13 +1165,6 @@ bool AsyncClient::free() {
   return false;
 }
 
-size_t AsyncClient::write(const char* data) {
-  if (data == NULL) {
-    return 0;
-  }
-  return write(data, strlen(data));
-}
-
 size_t AsyncClient::write(const char* data, size_t size, uint8_t apiflags) {
   size_t will_send = add(data, size, apiflags);
   if (!will_send || !send()) {

src/AsyncTCP.h

@@ -48,13 +48,16 @@ extern "C" {
   #include <semphr.h>
 }
   #define CONFIG_ASYNC_TCP_RUNNING_CORE -1 // any available core
-  #define CONFIG_ASYNC_TCP_USE_WDT      0
 #endif
 
 // If core is not defined, then we are running in Arduino or PIO
 #ifndef CONFIG_ASYNC_TCP_RUNNING_CORE
   #define CONFIG_ASYNC_TCP_RUNNING_CORE -1 // any available core
-  #define CONFIG_ASYNC_TCP_USE_WDT      1  // if enabled, adds between 33us and 200us per event
+#endif
+
+// guard AsyncTCP task with watchdog
+#ifndef CONFIG_ASYNC_TCP_USE_WDT
+  #define CONFIG_ASYNC_TCP_USE_WDT 1
 #endif
 
 #ifndef CONFIG_ASYNC_TCP_STACK_SIZE
@@ -106,34 +109,86 @@ class AsyncClient {
     bool connect(const IPv6Address& ip, uint16_t port);
 #endif
     bool connect(const char* host, uint16_t port);
+    /**
+     * @brief close connection
+     *
+     * @param now - ignored
+     */
     void close(bool now = false);
-    void stop();
+    // same as close()
+    void stop() { close(false); };
     int8_t abort();
     bool free();
 
-    bool canSend();                                                                      // ack is not pending
-    size_t space();                                                                      // space available in the TCP window
-    size_t add(const char* data, size_t size, uint8_t apiflags = ASYNC_WRITE_FLAG_COPY); // add for sending
-    bool send();                                                                         // send all data added with the method above
+    // ack is not pending
+    bool canSend();
+    // TCP buffer space available
+    size_t space();
 
-    // write equals add()+send()
-    size_t write(const char* data);
-    size_t write(const char* data, size_t size, uint8_t apiflags = ASYNC_WRITE_FLAG_COPY); // only when canSend() == true
+    /**
+     * @brief add data to be send (but do not send yet)
+     * @note add() would call lwip's tcp_write()
+        By default apiflags=ASYNC_WRITE_FLAG_COPY
+        You could try to use apiflags with this flag unset to pass data by reference and avoid copy to socket buffer,
+        but looks like it does not work for Arduino's lwip in ESP32/IDF at least
+        it is enforced in https://github.com/espressif/esp-lwip/blob/0606eed9d8b98a797514fdf6eabb4daf1c8c8cd9/src/core/tcp_out.c#L422C5-L422C30
+        if LWIP_NETIF_TX_SINGLE_PBUF is set, and it is set indeed in IDF
+        https://github.com/espressif/esp-idf/blob/a0f798cfc4bbd624aab52b2c194d219e242d80c1/components/lwip/port/include/lwipopts.h#L744
+     *
+     * @param data
+     * @param size
+     * @param apiflags
+     * @return size_t amount of data that has been copied
+     */
+    size_t add(const char* data, size_t size, uint8_t apiflags = ASYNC_WRITE_FLAG_COPY);
+
+    /**
+     * @brief send data previously add()'ed
+     *
+     * @return true on success
+     * @return false on error
+     */
+    bool send();
+
+    /**
+     * @brief add and enqueue data for sending
+     * @note it is same as add() + send()
+     * @note only make sense when canSend() == true
+     *
+     * @param data
+     * @param size
+     * @param apiflags
+     * @return size_t
+     */
+    size_t write(const char* data, size_t size, uint8_t apiflags = ASYNC_WRITE_FLAG_COPY);
+
+    /**
+     * @brief add and enque data for sending
+     * @note treats data as null-terminated string
+     *
+     * @param data
+     * @return size_t
+     */
+    size_t write(const char* data) { return data == NULL ? 0 : write(data, strlen(data)); };
 
     uint8_t state();
     bool connecting();
     bool connected();
     bool disconnecting();
     bool disconnected();
-    bool freeable(); // disconnected or disconnecting
+
+    // disconnected or disconnecting
+    bool freeable();
 
     uint16_t getMss();
 
     uint32_t getRxTimeout();
-    void setRxTimeout(uint32_t timeout); // no RX data timeout for the connection in seconds
+    // no RX data timeout for the connection in seconds
+    void setRxTimeout(uint32_t timeout);
 
     uint32_t getAckTimeout();
-    void setAckTimeout(uint32_t timeout); // no ACK timeout for the last sent packet in milliseconds
+    // no ACK timeout for the last sent packet in milliseconds
+    void setAckTimeout(uint32_t timeout);
 
     void setNoDelay(bool nodelay);
     bool getNoDelay();
@@ -162,23 +217,34 @@ class AsyncClient {
     IPAddress localIP();
     uint16_t localPort();
 
-    void onConnect(AcConnectHandler cb, void* arg = 0);    // on successful connect
-    void onDisconnect(AcConnectHandler cb, void* arg = 0); // disconnected
-    void onAck(AcAckHandler cb, void* arg = 0);            // ack received
-    void onError(AcErrorHandler cb, void* arg = 0);        // unsuccessful connect or error
-    void onData(AcDataHandler cb, void* arg = 0);          // data received (called if onPacket is not used)
-    void onPacket(AcPacketHandler cb, void* arg = 0);      // data received
-    void onTimeout(AcTimeoutHandler cb, void* arg = 0);    // ack timeout
-    void onPoll(AcConnectHandler cb, void* arg = 0);       // every 125ms when connected
+    // set callback - on successful connect
+    void onConnect(AcConnectHandler cb, void* arg = 0);
+    // set callback - disconnected
+    void onDisconnect(AcConnectHandler cb, void* arg = 0);
+    // set callback - ack received
+    void onAck(AcAckHandler cb, void* arg = 0);
+    // set callback - unsuccessful connect or error
+    void onError(AcErrorHandler cb, void* arg = 0);
+    // set callback - data received (called if onPacket is not used)
+    void onData(AcDataHandler cb, void* arg = 0);
+    // set callback - data received
+    void onPacket(AcPacketHandler cb, void* arg = 0);
+    // set callback - ack timeout
+    void onTimeout(AcTimeoutHandler cb, void* arg = 0);
+    // set callback - every 125ms when connected
+    void onPoll(AcConnectHandler cb, void* arg = 0);
 
-    void ackPacket(struct pbuf* pb);      // ack pbuf from onPacket
-    size_t ack(size_t len);               // ack data that you have not acked using the method below
-    void ackLater() { _ack_pcb = false; } // will not ack the current packet. Call from onData
+    // ack pbuf from onPacket
+    void ackPacket(struct pbuf* pb);
+    // ack data that you have not acked using the method below
+    size_t ack(size_t len);
+    // will not ack the current packet. Call from onData
+    void ackLater() { _ack_pcb = false; }
 
     const char* errorToString(int8_t error);
     const char* stateToString();
 
-    // Do not use any of the functions below!
+    // internal callbacks - Do NOT call any of the functions below in user code!
     static int8_t _s_poll(void* arg, struct tcp_pcb* tpcb);
     static int8_t _s_recv(void* arg, struct tcp_pcb* tpcb, struct pbuf* pb, int8_t err);
     static int8_t _s_fin(void* arg, struct tcp_pcb* tpcb, int8_t err);