servlet: disable RECYCLE_FACADES to reduce flaky tests (1.76.x backport) #12633
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Set discardFacades=false in Tomcat 10 Embedded to avoid premature OutputBuffer recycling. This works around flaky tests in gRPC servlet transport by ensuring facades are not discarded too early. Fixes grpc#12524
kannanjgithub
approved these changes
Jan 27, 2026
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Background
In the gRPC servlet transport with Tomcat 10 Embedded,
we observed occasional flaky tests in
grpc-servlet-jakarta:tomcat10Test.The issue is related to a race condition where the OutputBuffer is prematurely recycled during asynchronous writes.
Changes
Reference: spring-projects/spring-boot#36763 (comment)
This PR explicitly calls
.setDiscardFacades(false)on the Tomcat 10 Embedded Connector.The intention is to prevent outputBuffer reuse, so that the above race condition does not occur during tests.
Purpose
grpc-servlet-jakarta:tomcat10TestNote
This change aligns Tomcat 10 Embedded behavior with Tomcat 9 (where
RECYCLE_FACADESdefaults tofalse), and is known to prevent prematureOutputBufferrecycling during async writes.Based on the investigation and prior reports (e.g., Spring Boot discussion),
this is currently the correct and safe configuration for servlet-based asynchronous responses in Tomcat 10.
Fixes #12524
Backport of #12530