fix(profiling): Cancel a pending stop when the profiler is started again

A stop request only sets shouldStop, and the profiler stops when the
current chunk ends. A start call before that was ignored because the
profiler was still running, and shouldStop stayed set. So the profiler
stopped at the end of the chunk, even in TRACE mode while sampled spans
were active. The legacy profiler also never reset shouldStop, so after
the first stop every later profile ended after one chunk.

Reset shouldStop on every sampled start call in AndroidContinuousProfiler
and PerfettoContinuousProfiler. A manual start while the profiler runs
is now an expected call, so the Perfetto profiler logs it at DEBUG
level like the legacy profiler.

Author: alwx

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 ### Fixes
 
+- Keep UI profiling running when `startProfiler` is called before a requested stop takes effect at the end of the current chunk ([#XXXX](https://github.com/getsentry/sentry-java/pull/XXXX))
+  - Before, the start call was ignored and the profiler still stopped at the end of the chunk, even in `TRACE` mode while sampled spans were active. On API 34 and lower, every later profile also stopped after one chunk.
 - Keep sending events from Android 7.1.0 and older devices after Sentry changes its TLS certificate authority ([#6227](https://github.com/getsentry/sentry-java/pull/6227))
   - In February 2027, Sentry moves its TLS certificates from DigiCert to Let's Encrypt and Google Trust Services ([announcement](https://sentry.io/changelog/were-changing-our-tls-certificate-authority-in-february-2027)).
   - Android 7.1.0 (API 25) and older don't trust the Let's Encrypt root certificate (ISRG Root X1), so without this fix, the SDK on those devices can no longer send events to Sentry after the switch.

sentry-android-core/src/main/java/io/sentry/android/core/AndroidContinuousProfiler.java

@@ -131,6 +131,8 @@ public void startProfiler(
         logger.log(SentryLevel.DEBUG, "Profiler was not started due to sampling decision.");
         return;
       }
+      // A stop only takes effect when the current chunk ends, so a start before then cancels it.
+      shouldStop = false;
       switch (profileLifecycle) {
         case TRACE:
           // rootSpanCounter should never be negative, unless the user changed profile lifecycle

sentry-android-core/src/main/java/io/sentry/android/core/PerfettoContinuousProfiler.java

@@ -141,23 +141,22 @@ public void startProfiler(
         logger.log(SentryLevel.DEBUG, "Profiler was not started due to sampling decision.");
         return;
       }
+      // A stop only takes effect when the current chunk ends, so a start before then cancels it.
+      shouldStop = false;
       switch (profileLifecycle) {
         case TRACE:
           activeTraceCount = Math.max(0, activeTraceCount); // safety check.
           activeTraceCount++;
           break;
         case MANUAL:
           if (isRunning()) {
-            logger.log(
-                SentryLevel.WARNING,
-                "Unexpected call to startProfiler(MANUAL) while profiler already running. Skipping.");
+            logger.log(SentryLevel.DEBUG, "Profiler is already running.");
             return;
           }
           break;
       }
       if (!isRunning()) {
         logger.log(SentryLevel.DEBUG, "Started Profiler.");
-        shouldStop = false;
         startInternal();
       }
     }

sentry-android-core/src/test/java/io/sentry/android/core/AndroidContinuousProfilerTest.kt

@@ -278,6 +278,18 @@ class AndroidContinuousProfilerTest {
       }
       .testDoesNotStartWhenOffline(mocks)
 
+  @Test
+  fun `manual start cancels a pending stop`() =
+    fixture.getSut().testManualStartCancelsPendingStop(mocks)
+
+  @Test
+  fun `trace start cancels a pending stop`() =
+    fixture.getSut().testTraceStartCancelsPendingStop(mocks)
+
+  @Test
+  fun `manual profiler can be started again after a full start-stop cycle`() =
+    fixture.getSut().testCanBeStartedAgainAfterStopCycle(mocks)
+
   // -- Legacy-specific tests (AndroidContinuousProfiler only) --
 
   @Test

sentry-android-core/src/test/java/io/sentry/android/core/ContinuousProfilerTestCases.kt

@@ -192,3 +192,23 @@ fun IContinuousProfiler.testCanBeStartedAgainAfterStopCycle(mocks: ProfilerMocks
   mocks.executor.runAll()
   assertTrue(isRunning, "shouldStop must be reset on start")
 }
+
+fun IContinuousProfiler.testManualStartCancelsPendingStop(mocks: ProfilerMocks) {
+  startProfiler(ProfileLifecycle.MANUAL, mocks.tracesSampler)
+  val profilerIdBeforeStop = profilerId
+  stopProfiler(ProfileLifecycle.MANUAL)
+  startProfiler(ProfileLifecycle.MANUAL, mocks.tracesSampler)
+  mocks.executor.runAll()
+  assertTrue(isRunning, "a start before the chunk ends must cancel the pending stop")
+  assertEquals(profilerIdBeforeStop, profilerId)
+}
+
+fun IContinuousProfiler.testTraceStartCancelsPendingStop(mocks: ProfilerMocks) {
+  startProfiler(ProfileLifecycle.TRACE, mocks.tracesSampler)
+  val profilerIdBeforeStop = profilerId
+  stopProfiler(ProfileLifecycle.TRACE)
+  startProfiler(ProfileLifecycle.TRACE, mocks.tracesSampler)
+  mocks.executor.runAll()
+  assertTrue(isRunning, "a start before the chunk ends must cancel the pending stop")
+  assertEquals(profilerIdBeforeStop, profilerId)
+}

sentry-android-core/src/test/java/io/sentry/android/core/PerfettoContinuousProfilerTest.kt

@@ -178,6 +178,14 @@ class PerfettoContinuousProfilerTest {
   fun `manual profiler can be started again after a full start-stop cycle`() =
     fixture.getSut().testCanBeStartedAgainAfterStopCycle(mocks)
 
+  @Test
+  fun `manual start cancels a pending stop`() =
+    fixture.getSut().testManualStartCancelsPendingStop(mocks)
+
+  @Test
+  fun `trace start cancels a pending stop`() =
+    fixture.getSut().testTraceStartCancelsPendingStop(mocks)
+
   // -- Perfetto-specific tests --
 
   @Test
@@ -503,10 +511,6 @@ class PerfettoContinuousProfilerTest {
     assertTrue(profiler.isRunning)
     profiler.startProfiler(ProfileLifecycle.MANUAL, fixture.mockTracesSampler)
     assertTrue(profiler.isRunning)
-    verify(fixture.mockLogger)
-      .log(
-        eq(SentryLevel.WARNING),
-        eq("Unexpected call to startProfiler(MANUAL) while profiler already running. Skipping."),
-      )
+    verify(fixture.mockLogger).log(eq(SentryLevel.DEBUG), eq("Profiler is already running."))
   }
 }