Interceptors for threads (start, exit)

doc/KafkaConsumerQuickStart.md

@@ -191,15 +191,11 @@ About `Error`'s `value()`s, there are 2 cases
 
 * How many threads would be created by a KafkaConsumer?
 
-    Excluding the user's main thread, if `enable.auto.commit` is `false`, the `KafkaConsumer` would start another (N + 2) threads in the background; otherwise, the `KafkaConsumer` would start (N + 3) background threads. (N means the number of BOOTSTRAP_SERVERS)
-
     1. Each broker (in the list of BOOTSTRAP_SERVERS) would take a seperate thread to transmit messages towards a kafka cluster server.
 
     2. Another 3 threads will handle internal operations, consumer group operations, and kinds of timers, etc.
 
-    3. To enable the auto commit, one more thread would be create, which keeps polling/processing the offset-commit callback event.
-
-    E.g, if a KafkaConsumer was created with property of `BOOTSTRAP_SERVERS=127.0.0.1:8888,127.0.0.1:8889,127.0.0.1:8890`, it would take 6 threads in total (including the main thread).
+    3. To enable the auto events-polling, one more background thread would be created, which keeps polling/processing the offset-commit callback event.
 
 * Which one of these threads will handle the callbacks?
 

doc/KafkaProducerQuickStart.md

@@ -199,19 +199,15 @@ Larger `QUEUE_BUFFERING_MAX_MESSAGES`/`QUEUE_BUFFERING_MAX_KBYTES` might help to
 
 ### How many threads would be created by a KafkaProducer?
 
-Excluding the user's main thread, `KafkaProducer` would start (N + 3) background threads. (N means the number of BOOTSTRAP_SERVERS)
-
 Most of these background threads are started internally by librdkafka.
 
 Here is a brief introduction what they're used for,
 
 1. Each broker (in the list of BOOTSTRAP_SERVERS) would take a separate thread to transmit messages towards a kafka cluster server.
 
-2. Another 2 background threads would handle internal operations and kinds of timers, etc.
-
-3. One more background thread to keep polling the delivery callback event.
+2. Another 2 threads would handle internal operations and kinds of timers, etc.
 
-E.g, if a `KafkaProducer` was created with property of `BOOTSTRAP_SERVERS=127.0.0.1:8888,127.0.0.1:8889,127.0.0.1:8890`, it would take 7 threads in total (including the main thread).
+3. To enale the auto events-polling, one more background thread would be created, which keeps polling the delivery callback event.
 
 ### Which one of these threads will handle the callbacks
 

include/kafka/AdminClient.h

@@ -28,7 +28,10 @@ class AdminClient: public KafkaClient
 public:
     explicit AdminClient(const Properties& properties)
         : KafkaClient(ClientType::AdminClient,
-                      KafkaClient::validateAndReformProperties(properties))
+                      KafkaClient::validateAndReformProperties(properties),
+                      ConfigCallbacksRegister{},
+                      EventsPollingOption::Auto,
+                      Interceptors{})
     {
     }
 

include/kafka/Interceptors.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <kafka/Project.h>
+
+#include <functional>
+
+
+namespace KAFKA_API { namespace clients {
+
+class Interceptors
+{
+public:
+    using ThreadStartCallback = std::function<void(const std::string&, const std::string&)>;
+    using ThreadExitCallback  = std::function<void(const std::string&, const std::string&)>;
+
+    Interceptors& onThreadStart(ThreadStartCallback cb) { _valid = true; _threadStartCb = std::move(cb); return *this; }
+    Interceptors& onThreadExit(ThreadExitCallback cb)   { _valid = true; _threadExitCb = std::move(cb);  return *this; }
+
+    ThreadStartCallback onThreadStart() const { return _threadStartCb; }
+    ThreadExitCallback  onThreadExit()  const { return _threadExitCb; }
+
+    bool empty() const { return !_valid; }
+
+private:
+    ThreadStartCallback _threadStartCb;
+    ThreadExitCallback  _threadExitCb;
+    bool                _valid  = false;
+};
+
+} } // end of KAFKA_API::clients
+

include/kafka/KafkaClient.h

@@ -4,6 +4,7 @@
 
 #include <kafka/BrokerMetadata.h>
 #include <kafka/Error.h>
+#include <kafka/Interceptors.h>
 #include <kafka/KafkaException.h>
 #include <kafka/Log.h>
 #include <kafka/Properties.h>
@@ -20,6 +21,7 @@
 #include <mutex>
 #include <string>
 #include <thread>
+#include <vector>
 
 
 namespace KAFKA_API { namespace clients {
@@ -168,10 +170,11 @@ class KafkaClient
 
     using ConfigCallbacksRegister = std::function<void(rd_kafka_conf_t*)>;
 
-    KafkaClient(ClientType                     clientType,
-                const Properties&              properties,
-                const ConfigCallbacksRegister& extraConfigRegister = ConfigCallbacksRegister{},
-                EventsPollingOption            eventsPollingOption = EventsPollingOption::Auto);
+    KafkaClient(ClientType                      clientType,
+                const Properties&               properties,
+                const ConfigCallbacksRegister&  extraConfigRegister,
+                EventsPollingOption             eventsPollingOption,
+                Interceptors                    interceptors);
 
     rd_kafka_t* getClientHandle() const { return _rk.get(); }
 
@@ -221,8 +224,11 @@ class KafkaClient
     Logger              _logger;
     StatsCallback       _statsCb;
     ErrorCallback       _errorCb;
-    rd_kafka_unique_ptr _rk;
+
     EventsPollingOption _eventsPollingOption;
+    Interceptors        _interceptors;
+
+    rd_kafka_unique_ptr _rk;
 
     static std::string getClientTypeString(ClientType type)
     {
@@ -239,6 +245,11 @@ class KafkaClient
     // Error callback (for librdkafka)
     static void errorCallback(rd_kafka_t* rk, int err, const char* reason, void* opaque);
 
+    // Interceptor callback (for librdkafka)
+    static rd_kafka_resp_err_t configInterceptorOnNew(rd_kafka_t* rk, const rd_kafka_conf_t* conf, void* opaque, char* errStr, std::size_t maxErrStrSize);
+    static rd_kafka_resp_err_t interceptorOnThreadStart(rd_kafka_t* rk, rd_kafka_thread_type_t threadType, const char* threadName, void* opaque);
+    static rd_kafka_resp_err_t interceptorOnThreadExit(rd_kafka_t* rk, rd_kafka_thread_type_t threadType, const char* threadName, void* opaque);
+
     // Log callback (for class instance)
     void onLog(int level, const char* fac, const char* buf) const;
 
@@ -248,6 +259,10 @@ class KafkaClient
     // Error callback (for class instance)
     void onError(const Error& error);
 
+    // Interceptor callback (for class instance)
+    void interceptThreadStart(const std::string& threadName, const std::string& threadType);
+    void interceptThreadExit(const std::string& threadName, const std::string& threadType);
+
     static const constexpr char* BOOTSTRAP_SERVERS = "bootstrap.servers";
     static const constexpr char* CLIENT_ID         = "client.id";
     static const constexpr char* LOG_LEVEL         = "log_level";
@@ -275,8 +290,9 @@ class KafkaClient
     class PollThread
     {
     public:
-        explicit PollThread(Pollable& pollable)
-            : _running(true), _thread(keepPolling, std::ref(_running), std::ref(pollable))
+        using InterceptorCb = std::function<void()>;
+        explicit PollThread(const InterceptorCb& entryCb, const InterceptorCb& exitCb, Pollable& pollable)
+            : _running(true), _thread(keepPolling, std::ref(_running), entryCb, exitCb, std::ref(pollable))
         {
         }
 
@@ -288,12 +304,19 @@ class KafkaClient
         }
 
     private:
-        static void keepPolling(std::atomic_bool& running, Pollable& pollable)
+        static void keepPolling(std::atomic_bool&       running,
+                                const InterceptorCb&    entryCb,
+                                const InterceptorCb&    exitCb,
+                                Pollable&               pollable)
         {
+            entryCb();
+
             while (running.load())
             {
                 pollable.poll(CALLBACK_POLLING_INTERVAL_MS);
             }
+
+            exitCb();
         }
 
         static constexpr int CALLBACK_POLLING_INTERVAL_MS = 10;
@@ -306,7 +329,10 @@ class KafkaClient
     {
         _pollable = std::make_unique<KafkaClient::PollableCallback>(pollableCallback);
 
-        if (isWithAutoEventsPolling()) _pollThread = std::make_unique<PollThread>(*_pollable);
+        auto entryCb = [this]() { interceptThreadStart("events-polling", "background"); };
+        auto exitCb =  [this]() { interceptThreadExit("events-polling", "background"); };
+
+        if (isWithAutoEventsPolling()) _pollThread = std::make_unique<PollThread>(entryCb, exitCb, *_pollable);
     }
 
     void stopBackgroundPollingIfNecessary()
@@ -331,8 +357,10 @@ inline
 KafkaClient::KafkaClient(ClientType                     clientType,
                          const Properties&              properties,
                          const ConfigCallbacksRegister& extraConfigRegister,
-                         EventsPollingOption            eventsPollingOption)
-    : _eventsPollingOption(eventsPollingOption)
+                         EventsPollingOption            eventsPollingOption,
+                         Interceptors                   interceptors)
+    : _eventsPollingOption(eventsPollingOption),
+      _interceptors(std::move(interceptors))
 {
     static const std::set<std::string> PRIVATE_PROPERTY_KEYS = { "max.poll.records" };
 
@@ -403,6 +431,13 @@ KafkaClient::KafkaClient(ClientType                     clientType,
     // Other Callbacks
     if (extraConfigRegister) extraConfigRegister(rk_conf.get());
 
+    // Interceptor
+    if (!_interceptors.empty())
+    {
+        Error result{ rd_kafka_conf_interceptor_add_on_new(rk_conf.get(), "on_new", KafkaClient::configInterceptorOnNew, nullptr) };
+        KAFKA_THROW_IF_WITH_ERROR(result);
+    }
+
     // Set client handler
     _rk.reset(rd_kafka_new((clientType == ClientType::KafkaConsumer ? RD_KAFKA_CONSUMER : RD_KAFKA_PRODUCER),
                            rk_conf.release(),  // rk_conf's ownship would be transferred to rk, after the "rd_kafka_new()" call
@@ -534,6 +569,50 @@ KafkaClient::errorCallback(rd_kafka_t* rk, int err, const char* reason, void* /*
     kafkaClient(rk).onError(error);
 }
 
+inline void
+KafkaClient::interceptThreadStart(const std::string& threadName, const std::string& threadType)
+{
+    if (const auto& cb = _interceptors.onThreadStart()) cb(threadName, threadType);
+}
+
+inline void
+KafkaClient::interceptThreadExit(const std::string& threadName, const std::string& threadType)
+{
+    if (const auto& cb = _interceptors.onThreadExit()) cb(threadName, threadType);
+}
+
+inline rd_kafka_resp_err_t
+KafkaClient::configInterceptorOnNew(rd_kafka_t* rk, const rd_kafka_conf_t* /*conf*/, void* opaque, char* /*errStr*/, std::size_t /*maxErrStrSize*/)
+{
+    if (auto result = rd_kafka_interceptor_add_on_thread_start(rk, "on_thread_start", KafkaClient::interceptorOnThreadStart, opaque))
+    {
+        return result;
+    }
+
+    if (auto result = rd_kafka_interceptor_add_on_thread_exit(rk, "on_thread_exit", KafkaClient::interceptorOnThreadExit, opaque))
+    {
+        return result;
+    }
+
+    return RD_KAFKA_RESP_ERR_NO_ERROR;
+}
+
+inline rd_kafka_resp_err_t
+KafkaClient::interceptorOnThreadStart(rd_kafka_t* rk, rd_kafka_thread_type_t threadType, const char* threadName, void* /*opaque*/)
+{
+    kafkaClient(rk).interceptThreadStart(threadName, toString(threadType));
+
+    return RD_KAFKA_RESP_ERR_NO_ERROR;
+}
+
+inline rd_kafka_resp_err_t
+KafkaClient::interceptorOnThreadExit(rd_kafka_t* rk, rd_kafka_thread_type_t threadType, const char* threadName, void* /*opaque*/)
+{
+    kafkaClient(rk).interceptThreadExit(threadName, toString(threadType));
+
+    return RD_KAFKA_RESP_ERR_NO_ERROR;
+}
+
 inline Optional<BrokerMetadata>
 KafkaClient::fetchBrokerMetadata(const std::string& topic, std::chrono::milliseconds timeout, bool disableErrorLogging)
 {

include/kafka/KafkaConsumer.h

@@ -39,8 +39,9 @@ class KafkaConsumer: public KafkaClient
      *   - RD_KAFKA_RESP_ERR__INVALID_ARG      : Invalid BOOTSTRAP_SERVERS property
      *   - RD_KAFKA_RESP_ERR__CRIT_SYS_RESOURCE: Fail to create internal threads
      */
-    explicit KafkaConsumer(const Properties&   properties,
-                           EventsPollingOption eventsPollingOption = EventsPollingOption::Auto);
+    explicit KafkaConsumer(const Properties&    properties,
+                           EventsPollingOption  eventsPollingOption = EventsPollingOption::Auto,
+                           const Interceptors&  interceptors        = Interceptors{});
 
     /**
      * The destructor for KafkaConsumer.
@@ -373,11 +374,14 @@ KafkaConsumer::registerConfigCallbacks(rd_kafka_conf_t* conf)
 }
 
 inline
-KafkaConsumer::KafkaConsumer(const Properties &properties, EventsPollingOption eventsPollingOption)
+KafkaConsumer::KafkaConsumer(const Properties&      properties,
+                             EventsPollingOption    eventsPollingOption,
+                             const Interceptors&    interceptors)
     : KafkaClient(ClientType::KafkaConsumer,
                   validateAndReformProperties(properties),
                   registerConfigCallbacks,
-                  eventsPollingOption)
+                  eventsPollingOption,
+                  interceptors)
 {
     // Pick up the "max.poll.records" property
     if (auto maxPollRecordsProperty = properties.getProperty(consumer::Config::MAX_POLL_RECORDS))

include/kafka/KafkaProducer.h

@@ -39,8 +39,9 @@ class KafkaProducer: public KafkaClient
      *   - RD_KAFKA_RESP_ERR__INVALID_ARG      : Invalid BOOTSTRAP_SERVERS property
      *   - RD_KAFKA_RESP_ERR__CRIT_SYS_RESOURCE: Fail to create internal threads
      */
-    explicit KafkaProducer(const Properties&   properties,
-                           EventsPollingOption eventsPollingOption = EventsPollingOption::Auto);
+    explicit KafkaProducer(const Properties&    properties,
+                           EventsPollingOption  eventsPollingOption = EventsPollingOption::Auto,
+                           const Interceptors&  interceptors        = Interceptors{});
 
     /**
      * The destructor for KafkaProducer.
@@ -221,11 +222,14 @@ class KafkaProducer: public KafkaClient
 };
 
 inline
-KafkaProducer::KafkaProducer(const Properties& properties, EventsPollingOption eventsPollingOption)
+KafkaProducer::KafkaProducer(const Properties&      properties,
+                             EventsPollingOption    eventsPollingOption,
+                             const Interceptors&    interceptors)
     : KafkaClient(ClientType::KafkaProducer,
                   validateAndReformProperties(properties),
                   registerConfigCallbacks,
-                  eventsPollingOption)
+                  eventsPollingOption,
+                  interceptors)
 {
     // Start background polling (if needed)
     startBackgroundPollingIfNecessary([this](int timeoutMs){ pollCallbacks(timeoutMs); });

include/kafka/RdKafkaHelper.h

@@ -6,6 +6,7 @@
 
 #include <librdkafka/rdkafka.h>
 
+#include <cassert>
 #include <memory>
 
 namespace KAFKA_API {
@@ -48,6 +49,23 @@ using rd_kafka_consumer_group_metadata_unique_ptr = std::unique_ptr<rd_kafka_con
 inline void RkErrorDeleter(rd_kafka_error_t* p) { rd_kafka_error_destroy(p); }
 using rd_kafka_error_shared_ptr = std::shared_ptr<rd_kafka_error_t>;
 
+
+inline std::string toString(rd_kafka_thread_type_t threadType)
+{
+    switch (threadType)
+    {
+        case RD_KAFKA_THREAD_MAIN:
+            return "main";
+        case RD_KAFKA_THREAD_BACKGROUND:
+            return "background";
+        case RD_KAFKA_THREAD_BROKER:
+            return "broker";
+        default:
+            assert(false);
+            return "NA";
+    }
+}
+
 // Convert from rd_kafka_xxx datatypes
 inline TopicPartitionOffsets getTopicPartitionOffsets(const rd_kafka_topic_partition_list_t* rk_tpos)
 {