artemlivshits commented on code in PR #14629:
URL: https://github.com/apache/kafka/pull/14629#discussion_r1375078778
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core/src/main/scala/kafka/server/KafkaRequestHandler.scala:
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@@ -53,25 +53,27 @@ object KafkaRequestHandler {
* Wrap callback to schedule it on a request thread.
* NOTE: this function must be called on a request thread.
* @param fun Callback function to execute
+ * @param requestLocal The RequestLocal for the current request handler
thread in case we need to call
+ * the callback function without queueing the callback
request
* @return Wrapped callback that would execute `fun` on a request thread
*/
- def wrap[T](fun: T => Unit): T => Unit = {
+ def wrap[T](fun: (RequestLocal, T) => Unit, requestLocal: RequestLocal): T
=> Unit = {
val requestChannel = threadRequestChannel.get()
val currentRequest = threadCurrentRequest.get()
if (requestChannel == null || currentRequest == null) {
if (!bypassThreadCheck)
throw new IllegalStateException("Attempted to reschedule to request
handler thread from non-request handler thread.")
- T => fun(T)
+ T => fun(requestLocal, T)
} else {
T => {
- if (threadCurrentRequest.get() != null) {
- // If the callback is actually executed on a request thread, we can
directly execute
+ if (threadCurrentRequest.get() == currentRequest) {
Review Comment:
Yeah, the hope is that we'd see more async patterns as we evolve Kafka, and
the way it's currently implemented, we just say "execute callback on the
_current_ thread pool", which is why the thread local is used -- this way we
can implement a non-blocking wait-and-continue-on-current-thread-pool from any
level without passing additional arguments through the whole stack. The same
functionality could be implemented on other thread pools, e.g. if the group
coordinator has its own thread pool, we could implement the same primitive
there as well.
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