perf(android): Parse app start profiling config without JsonSerializer (#5867)

* perf(android): Parse app start profiling config without JsonSerializer (JAVA-621)

SentryPerformanceProvider.launchAppStartProfiler ran in ContentProvider.onCreate
— main thread, before Application.onCreate, on every cold start — and built a
full JsonSerializer(SentryOptions.empty()) to read one small config file.

That path only ever reads options.getLogger(), but JsonSerializer's constructor
registers every known deserializer to use exactly one of them. Calling the
deserializer directly cuts the parse from 221 to 33 allocations and ~7.5us to
~3.7us (Pixel 10, androidx Microbenchmark, allocationCount is deterministic).

Malformed input still yields null so callers keep reporting it as a
deserialization failure rather than a read error.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

* changelog

* ref(android): Catch only expected exceptions when parsing profiling config

Narrow the deserialization catch from Throwable to Exception. The vendored JSON
reader signals bad input with IOException (MalformedJsonException, EOFException),
IllegalStateException on token type mismatch, and NumberFormatException on an
unparseable number — all Exception subclasses. Catching Throwable additionally
swallowed Error, which is never a recoverable "config file is bad" signal.

This also restores parity with JsonSerializer.deserialize, which catches
Exception, so the replaced behaviour is matched exactly rather than widened.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

* ref(android): Trim javadoc on deserializeProfilingConfig

Drop the paragraph enumerating which exception types the vendored JSON reader
throws. That catch (Exception) does not swallow Error is a language-level
given, and listing the reader's internal exception types invites the comment
to drift as that code changes. The rationale a reader cannot infer from the
code — why the deserializer is called directly, and why null is returned
instead of rethrowing — stays.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: runningcode

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Performance
 
 - Remove an unused lock from `SentryPerformanceProvider`, which was allocated on every cold start in `ContentProvider.onCreate` without ever being acquired ([#5871](https://github.com/getsentry/sentry-java/pull/5871))
+- Parse the app start profiling config with only the deserializer it needs instead of building a full `JsonSerializer` and `SentryOptions`, cutting 188 of 221 allocations on the main thread before `Application.onCreate` ([#5867](https://github.com/getsentry/sentry-java/pull/5867))
 
 ## 8.51.0
 

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

@@ -13,7 +13,7 @@
 import io.sentry.ILogger;
 import io.sentry.ISentryLifecycleToken;
 import io.sentry.ITransactionProfiler;
-import io.sentry.JsonSerializer;
+import io.sentry.JsonObjectReader;
 import io.sentry.SentryAppStartProfilingOptions;
 import io.sentry.SentryExecutorService;
 import io.sentry.SentryLevel;
@@ -117,8 +117,7 @@ private void launchAppStartProfiler(final @NotNull AppStartMetrics appStartMetri
     try (final @NotNull Reader reader =
             new BufferedReader(new InputStreamReader(new FileInputStream(configFile)))) {
       final @Nullable SentryAppStartProfilingOptions profilingOptions =
-          new JsonSerializer(SentryOptions.empty())
-              .deserialize(reader, SentryAppStartProfilingOptions.class);
+          deserializeProfilingConfig(reader);
 
       if (profilingOptions == null) {
         logger.log(
@@ -166,6 +165,25 @@ private void launchAppStartProfiler(final @NotNull AppStartMetrics appStartMetri
     }
   }
 
+  /**
+   * Parses the app start profiling config with only the deserializer it needs. Going through {@link
+   * io.sentry.JsonSerializer} would allocate a full {@link SentryOptions} plus every registered
+   * deserializer on the main thread before {@code Application.onCreate}, to use exactly one of
+   * them.
+   *
+   * <p>Returns null on malformed input, matching what {@code JsonSerializer.deserialize} did, so
+   * callers keep reporting it as a deserialization failure rather than a read error.
+   */
+  private @Nullable SentryAppStartProfilingOptions deserializeProfilingConfig(
+      final @NotNull Reader reader) {
+    try (final @NotNull JsonObjectReader jsonReader = new JsonObjectReader(reader)) {
+      return new SentryAppStartProfilingOptions.Deserializer().deserialize(jsonReader, logger);
+    } catch (Exception e) {
+      logger.log(SentryLevel.ERROR, "Error when deserializing", e);
+      return null;
+    }
+  }
+
   private void createAndStartContinuousProfiler(
       final @NotNull Context context,
       final @NotNull SentryAppStartProfilingOptions profilingOptions,

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

@@ -153,6 +153,21 @@ class SentryPerformanceProviderTest {
       )
   }
 
+  @Test
+  fun `when config file is malformed, profiler is not started`() {
+    fixture.getSut { config -> config.writeText("{\"profile_sampled\": tru") }
+    assertNull(AppStartMetrics.getInstance().appStartProfiler)
+    assertNull(AppStartMetrics.getInstance().appStartContinuousProfiler)
+    verify(fixture.logger).log(eq(SentryLevel.ERROR), eq("Error when deserializing"), any())
+    verify(fixture.logger)
+      .log(
+        eq(SentryLevel.WARNING),
+        eq(
+          "Unable to deserialize the SentryAppStartProfilingOptions. App start profiling will not start."
+        ),
+      )
+  }
+
   @Test
   fun `when profiling is disabled, profiler is not started`() {
     fixture.getSut { config ->