Real-time threads: periodic SCHED_FIFO loops the collector never stops

.github/workflows/embedded-linux.yml

@@ -26,6 +26,7 @@ on:
       - 'vm/JavaAPI/src/**'
       - 'maven/linux/**'
       - 'scripts/embedded/**'
+      - 'vm/backend/**'
       - '.github/workflows/embedded-linux.yml'
   pull_request:
     paths:
@@ -35,6 +36,7 @@ on:
       - 'vm/JavaAPI/src/**'
       - 'maven/linux/**'
       - 'scripts/embedded/**'
+      - 'vm/backend/**'
       - '.github/workflows/embedded-linux.yml'
 
 concurrency:
@@ -70,7 +72,7 @@ jobs:
           RETRY_DELAY_SECONDS: '60'
         run: |
           cd maven
-          bash ../scripts/ci/retry.sh mvn -B -pl core,linux -am install \
+          bash ../scripts/ci/retry.sh mvn -B -pl core,linux,backend,codenameone-maven-plugin -am install \
             -DskipTests -Dmaven.javadoc.skip=true -Plocal-dev-javase \
             -Dspotbugs.skip=true -Dpmd.skip=true -Dcheckstyle.skip=true \
             -Dmaven.repo.local="$GITHUB_WORKSPACE/.m2-repo"
@@ -119,6 +121,24 @@ jobs:
             --reference "$B/result/frame60.png" "$B/result/gpu/demo.log" "$B/result/gpu/frame60.png" \
             "$GITHUB_STEP_SUMMARY"
 
+      # The real-time check (vm/backend/demo/rtcheck): a 1 kHz loop beside a thread
+      # that keeps the collector busy, a cycle that allocates where the build cannot
+      # see it, and the memory limit. Run as root so SCHED_FIFO and mlockall apply.
+      # The runner's kernel is not PREEMPT_RT and its cores are shared, so the
+      # latency is reported and bounded loosely (20ms): what this gates is that the
+      # collector never stops the loop, which shows up as a missed run of periods,
+      # not as tens of microseconds.
+      - name: Real-time threads under collector load
+        run: |
+          bash scripts/ci/apt-get-update.sh
+          sudo apt-get install -y clang libssl-dev libnghttp2-dev libcurl4-openssl-dev
+          export JDK_8_HOME="$JAVA_HOME"
+          (cd vm/backend && CN1_BACKEND_DEMO=demo/rtcheck \
+            ./build.sh RtCheck com.demo "$RUNNER_TEMP/rtcheck")
+          sudo timeout 120 "$RUNNER_TEMP/rtcheck" 10 20000 | tee "$RUNNER_TEMP/rtcheck.log"
+          grep '^RTCHECK' "$RUNNER_TEMP/rtcheck.log" >> "$GITHUB_STEP_SUMMARY"
+          grep -q '^RTCHECK OK' "$RUNNER_TEMP/rtcheck.log"
+
       - name: Upload the run
         if: always()
         uses: actions/upload-artifact@v4

.github/workflows/parparvm-tests.yml

@@ -44,6 +44,7 @@ on:
       - 'CodenameOne/src/com/codename1/impl/SharedWithBackend.java'
       - 'CodenameOne/src/com/codename1/impl/orm/**'
       - 'CodenameOne/src/com/codename1/hardware/**'
+      - 'CodenameOne/src/com/codename1/realtime/**'
       - 'CodenameOne/src/com/codename1/qrcode/QrCode.java'
       - 'CodenameOne/src/com/codename1/impl/MdnsEngine.java'
       - 'CodenameOne/src/com/codename1/orm/session/**'
@@ -130,6 +131,7 @@ on:
       - 'CodenameOne/src/com/codename1/impl/SharedWithBackend.java'
       - 'CodenameOne/src/com/codename1/impl/orm/**'
       - 'CodenameOne/src/com/codename1/hardware/**'
+      - 'CodenameOne/src/com/codename1/realtime/**'
       - 'CodenameOne/src/com/codename1/qrcode/QrCode.java'
       - 'CodenameOne/src/com/codename1/impl/MdnsEngine.java'
       - 'CodenameOne/src/com/codename1/orm/session/**'

CodenameOne/src/com/codename1/impl/CodenameOneImplementation.java

@@ -8703,6 +8703,13 @@ public com.codename1.hardware.Hardware getHardware() {
         return null;
     }
 
+    /// Returns the port's real-time entry point. Default implementation returns
+    /// `null`, which leaves [com.codename1.realtime.Realtime#getInstance()] on its
+    /// best-effort Java default; ports with real-time scheduling override this.
+    public com.codename1.realtime.Realtime getRealtime() {
+        return null;
+    }
+
     /// Returns the port-specific local calendar source, or null when the port
     /// has no device calendar integration.
     public com.codename1.calendar.LocalCalendarSource getLocalCalendarSource() {

CodenameOne/src/com/codename1/realtime/AllocationAllowed.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2026, Codename One and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Codename One designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Codename One through http://www.codenameone.com/ if you
+ * need additional information or have any questions.
+ */
+package com.codename1.realtime;
+
+/// Marks a method that a [RealtimeTask]'s `cycle()` may call although it allocates.
+///
+/// The build checks every method that `cycle()` and `periodsMissed(int)` reach and
+/// fails on an allocation. This annotation tells the check to stop at the marked method
+/// instead, for a path that allocates only in a case the application has accounted for,
+/// such as a rare event that is logged. At run time such a path still counts against the
+/// thread's allocation budget ([RealtimeParameters#setAllocationBudget(int)]); with the
+/// default budget of zero it ends the steady state with a [RealtimeAllocationError].
+@java.lang.annotation.Retention(java.lang.annotation.RetentionPolicy.CLASS)
+@java.lang.annotation.Target({java.lang.annotation.ElementType.METHOD, java.lang.annotation.ElementType.CONSTRUCTOR})
+@com.codename1.impl.SharedWithBackend
+public @interface AllocationAllowed {
+}