Dozens of "HttpClient-N-SelectorManager" threads created

[Ruslan Ibragimov]

I encounter strange behavior of java.net.http.HttpClient in my application running in amazoncorretto:17.0.13, after some time instead of just one HttpClient-1-SelectorManager thread I'm starting observing dozens of such threads.

I'm creating only one instance of HttpClient in whole application, and confirming with logging that following snippet called only once:

val httpClient = HttpClient.newBuilder()
    .version(HttpClient.Version.*HTTP_2*)
    .followRedirects(HttpClient.Redirect.*NEVER*)
    .connectTimeout(Duration.ofSeconds(60))
    .build()

I also verified that no dependencies using HttpClient under the hood.

"HttpClient-18-SelectorManager" #20791 daemon prio=5 os_prio=0 cpu=31.77ms elapsed=3679.62s allocated=178K defined_classes=0 tid=0x00007f212c5dfce0 nid=0x541f runnable  [0x00007f21993ee000]
   java.lang.Thread.State: RUNNABLE
	at sun.nio.ch.EPoll.wait(java.base at 17.0.13/Native Method)
	at sun.nio.ch.EPollSelectorImpl.doSelect(java.base at 17.0.13/EPollSelectorImpl.java:118)
	at sun.nio.ch.SelectorImpl.lockAndDoSelect(java.base at 17.0.13/SelectorImpl.java:129)
	- locked <0x000000008c488e38> (a sun.nio.ch.Util$2)
	- locked <0x000000008c488de8> (a sun.nio.ch.EPollSelectorImpl)
	at sun.nio.ch.SelectorImpl.select(java.base at 17.0.13/SelectorImpl.java:141)
	at jdk.internal.net.http.HttpClientImpl$SelectorManager.run(java.net.http at 17.0.13/HttpClientImpl.java:894)

   Locked ownable synchronizers:
	- None


So now I'm in situation when I see a lot (a few times they grow to 150+ threads) of such threads created over time and stay alive. I believe it's also hurting application performance which lead even to timeouts on http stack (but this is unconfirmed).

Any hint to understand why this might happen and how to debug root cause would be appreciated.

--
Best regards,
Ruslan Ibragimov
https://heapy.io/
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.org/pipermail/net-dev/attachments/20250123/9b4c5b05/attachment.htm>