Case study: Debug an ANR

This page walks through how to debug an Application Not Responding (ANR) error using ProfilingManager with an example system trace.

Set up app to collect ANRs

Start by setting up an ANR trigger in your app:

Kotlin

fun addANRTrigger() {
    val profilingManager =
        applicationContext.getSystemService(ProfilingManager::class.java) ?: return
    val triggers = ArrayList<ProfilingTrigger>()
    val triggerBuilder = ProfilingTrigger.Builder(ProfilingTrigger.TRIGGER_TYPE_ANR)
    triggers.add(triggerBuilder.build())
    val callbackExecutor: Executor = Executors.newSingleThreadExecutor()
    val resultCallback = Consumer<ProfilingResult> { profilingResult ->
        // Handle uploading trace to your back-end
    }
    profilingManager.registerForAllProfilingResults(callbackExecutor, resultCallback)
    profilingManager.addProfilingTriggers(triggers)
}

Java

public void addANRTrigger() {
  ProfilingManager profilingManager = getApplicationContext().getSystemService(
      ProfilingManager.class);
  List<ProfilingTrigger> triggers = new ArrayList<>();
  ProfilingTrigger.Builder triggerBuilder = new ProfilingTrigger.Builder(
      ProfilingTrigger.TRIGGER_TYPE_ANR);
  triggers.add(triggerBuilder.build());
  Executor callbackExecutor = Executors.newSingleThreadExecutor();
  Consumer<ProfilingResult> resultCallback =
      profilingResult -> {
        // Handle uploading trace to your back-end
      };
  profilingManager.registerForAllProfilingResults(callbackExecutor, resultCallback);
  profilingManager.addProfilingTriggers(triggers);
}

After capturing and uploading an ANR trace, you can inspect it manually in the Perfetto UI as shown in the following steps, or automate the ANR investigation with an AI agent.

Analyze the trace

Because the ANR triggered the trace, you know the trace ended when the system detected unresponsiveness in your app's main thread (or when another timeout occurred). Figure 1 shows how to navigate to your app's main thread, which is tagged accordingly within the UI.

Perfetto UI navigation to app main thread.
Figure 1. Navigation to app's main thread.

The end of the trace matches the ANR's timestamp, as shown in Figure 2.

Perfetto UI showing the end of a trace, highlighting the ANR trigger location.
Figure 2. ANR trigger location.

When the ANR occurred, the main thread was executing the handleNetworkResponse slice inside MyApp:SubmitButton, which consumed 1.48 seconds of CPU time (Figure 3).

Perfetto UI showing the CPU time consumed by the handleNetworkResponse execution at the time of the ANR.
Figure 3. Execution at the time of ANR.

Relying only on a stack dump taken at the moment of the ANR might misattribute the freeze entirely to handleNetworkResponse. However, 1.48 seconds isn't long enough on its own to trigger an ANR, so you need to inspect what blocked the main thread earlier.

Start by locating the last UI frame rendered before the freeze (Choreographer#doFrame 551275), which immediately precedes the MyApp:SubmitButton slice (Figure 4).

Perfetto UI showing last frame rendered by UI thread prior the ANR.
Figure 4. Last app frame generated before the ANR.

To understand the blockage, zoom out to inspect the full MyApp:SubmitButton slice. You will notice a critical detail in the thread states for the manually selected range in Figure 5: the thread spent roughly 75% of the time (6.7 seconds) in Sleeping state and only 24% of the time in Running state.

Perfetto UI showing thread states during an operation, highlighting 75% sleeping and 24% running time.
Figure 5. Thread states during MyApp:SubmitButton operation.

This indicates that the primary cause of the ANR was waiting, not computation. Examine the individual sleep occurrences to find a pattern.

Perfetto UI showing the first sleeping interval within the MyAppSubmitButton trace slice.
Figure 6. First sleeping time within MyApp:SubmitButton.
Perfetto UI showing the second sleeping interval within the MyAppSubmitButton trace slice.
Figure 7. Second sleeping time within MyApp:SubmitButton.
Perfetto UI showing the third sleeping interval within the MyAppSubmitButton trace slice.
Figure 8. Third sleeping time within MyApp:SubmitButton.
Perfetto UI showing the fourth sleeping interval within the MyAppSubmitButton trace slice.
Figure 9. Fourth sleeping time within MyApp:SubmitButton.

The first three sleep intervals (Figures 6–8) are approximately 2 seconds each, and the fourth interval (Figure 9) is 0.7 seconds. Repeated 2-second pauses strongly suggest a programmed timeout that retried three times before succeeding on the fourth attempt—accumulating enough delay to trigger an ANR (Figure 10).

Perfetto UI showing a summary of delays during the MyApp:SubmitButton trace slice, indicating multiple 2-second sleep intervals.
Figure 10. Summary of delays during MyApp:SubmitButton slice.

Identify the root cause in code

To verify this hypothesis, inspect the code associated with the MyApp:SubmitButton trace section:

Kotlin

fun setupButtonCallback() {
    findViewById<View>(R.id.submit).setOnClickListener {
        trace("MyApp:SubmitButton") {
            onClickSubmit()
        }
    }
}

fun onClickSubmit() {
    prepareNetworkRequest()

    var networkRequestSuccess = false
    var maxAttempts = 10
    while (!networkRequestSuccess && maxAttempts > 0) {
        networkRequestSuccess = performNetworkRequest(NETWORK_TIMEOUT_MILLISECS)
        maxAttempts--
    }

    if (networkRequestSuccess) {
        handleNetworkResponse()
    }
}

fun performNetworkRequest(timeoutMilliseconds: Int): Boolean {
    // ...
}

fun prepareNetworkRequest() {
    // ...
}

fun handleNetworkResponse() {
    trace("handleNetworkResponse") {
        // ...
    }
}

companion object {
    private const val NETWORK_TIMEOUT_MILLISECS = 2000
}

Java

private static final int NETWORK_TIMEOUT_MILLISECS = 2000;
public void setupButtonCallback() {
  findViewById(R.id.submit).setOnClickListener(submitButtonView -> {
    Trace.beginSection("MyApp:SubmitButton");
    onClickSubmit();
    Trace.endSection();
  });
}

public void onClickSubmit() {
  prepareNetworkRequest();

  boolean networkRequestSuccess = false;
  int maxAttempts = 10;
  while (!networkRequestSuccess && maxAttempts > 0) {
    networkRequestSuccess = performNetworkRequest(NETWORK_TIMEOUT_MILLISECS);
    maxAttempts--;
  }

  if (networkRequestSuccess) {
    handleNetworkResponse();
  }
}

boolean performNetworkRequest(int timeoutMiliseconds) {
  // ...
}


void prepareNetworkRequest() {
  // ...
}

public void handleNetworkResponse() {
  Trace.beginSection("handleNetworkResponse");
  // ...
  Trace.endSection();
}

The code confirms this hypothesis. The onClickSubmit method executes a network request on the UI thread with a hardcoded NETWORK_TIMEOUT_MILLISECS of 2000ms. Crucially, it runs inside a while loop that retries up to 10 times.

In this specific trace, the user likely had poor network connectivity. The first three attempts failed, causing three 2-second timeouts (a total of 6 seconds). The fourth attempt succeeded after 0.7 seconds, allowing the code to proceed to handleNetworkResponse. However, the accumulated wait time already triggered the ANR.

Fix the ANR

Avoid this type of ANR by moving network-related operations that have varying latencies to a background thread instead of executing them on the main thread. This keeps the UI responsive even with poor connectivity, eliminating this class of ANRs.

Automate the ANR investigation with an AI agent

Instead of manually inspecting timelines and sleep intervals in the Perfetto UI, you can use an AI coding agent configured with the Perfetto AI skill to query the ANR trace and correlate it with your codebase:

Analyze the Perfetto system trace at </path/to/trace.perfetto-trace>, which
corresponds to an ANR trace, and find the root cause of the ANR using the
Perfetto AI skill. The codebase is located at </path/to/codebase>.

The agent queries the trace with trace_processor and reaches the same conclusion as the manual investigation—without getting misled by the unfinished handleNetworkResponse slice at the end of the trace. It identifies that MyApp:SubmitButton blocked the main thread for over 9.2 seconds, reconstructs the three 2-second network timeouts and 0.7-second fourth attempt in performNetworkRequest alongside the CPU busy-wait loops in prepareNetworkRequest and handleNetworkResponse, and maps each phase to ProfilingManagerJavaSnippets.java with a recommendation to move onClickSubmit off the UI thread:

# Perfetto ANR Root-Cause Analysis Report

* **Source Code:** `ProfilingManagerJavaSnippets.java`
* **Target Process:** `com.example.sampleapp` (`pid = 32579`, `upid = 27`)
* **Blocked Thread:** Main UI thread `ample.sampleapp` (`tid = 32579`, `utid = 760`)
* **Collection Mechanism:** Android `ProfilingManager` (`ProfilingTrigger.TRIGGER_TYPE_ANR`)

---

## 1. Executive Summary

> **Important:** The ANR in `com.example.sampleapp` is caused by executing **synchronous, blocking network retry logic (`Thread.sleep`) and heavy CPU busy-wait loops (`cpuIntensiveComputation`) directly on the main UI thread** inside the submit button click listener (`MyApp:SubmitButton` -> `onClickSubmit()`).

When the user taps the submit button at `7,967.78 ms` into the trace (`ts = 80459171444519`), the main UI thread is blocked continuously for **more than `9,281.30 ms`** (still unfinished when the trace ends at `17,249.08 ms`):

1. **`prepareNetworkRequest()`** runs a CPU busy-wait loop on the main thread for **`~1,019 ms`**.
2. **`performNetworkRequest(2000)`** executes in a synchronous `while` retry loop on the main thread. Each attempt begins with **`20 ms`** of CPU busy-waiting followed by a `Thread.sleep()`. The request times out (`2,000 ms` sleep) **3 times in a row** and succeeds on the **4th attempt** (`~701 ms` sleep), blocking the main thread for **`~6,764 ms`** across the 4 attempts (`6,703.18 ms` sleeping + `~60 ms` CPU).
3. **`handleNetworkResponse()`** begins at **`+7,783.44 ms`** after the button click and runs another `2,000 ms` CPU busy-wait loop on the main thread (`1,497.86 ms` captured before the trace ends).

    [Touch UP & Click (t = +0 ms)]
      -> prepareNetworkRequest() (~1,000 ms CPU Busy-Wait)
      -> Attempt #1 (Timeout: 20 ms CPU + 2,001 ms Sleep)
      -> Attempt #2 (Timeout: 20 ms CPU + 2,001 ms Sleep)
      -> Attempt #3 (Timeout: 20 ms CPU + 2,001 ms Sleep, crosses 5s ANR threshold)
      -> Attempt #4 (Success: 20 ms CPU + 701 ms Sleep)
      -> handleNetworkResponse() (1,498 ms CPU, unfinished at trace end)

## 2. PerfettoSQL Trace Analysis

### 2.1 Open Main-Thread Slices at Trace End

Querying `thread_or_process_slice` on the main thread (`utid = 760`) around and after the touch event shows that `MyApp:SubmitButton` and its nested slice `handleNetworkResponse` both have `dur = -1` (still open when the trace completed):

```sql
INCLUDE PERFETTO MODULE slices.with_context;

SELECT
  id,
  ts,
  (ts - trace_start()) / 1e6 AS rel_ts_ms,
  dur,
  IIF(dur = -1, trace_end() - ts, dur) / 1e6 AS effective_dur_ms,
  depth,
  name
FROM thread_or_process_slice
WHERE utid = 760 AND ts >= 80459169800000
ORDER BY ts;
```

| Slice ID | Slice Name | Start (`ts` ns) | Offset from Trace Start | Raw `dur` | Effective Duration (to trace end) | Depth |
| :--- | :--- | :--- | :--- | :--- | :--- | :--- |
| `40070` | `dispatchInputEvent MotionEvent UP` | `80459169801575` | `7,966.14 ms` | `190,633 ns` | `0.19 ms` | `0` |
| `40156` | **`MyApp:SubmitButton`** | `80459171444519` | `7,967.78 ms` | `-1` | **`9,281.30 ms`** | `0` |
| `97500` | **`handleNetworkResponse`** | `80466954886580` | `15,751.23 ms` | `-1` | **`1,497.86 ms`** | `1` |

---

### 2.2 Aggregate Main-Thread State (`thread_state`) During `MyApp:SubmitButton`

Aggregating `thread_state` for `utid = 760` from the start of `MyApp:SubmitButton` (`ts >= 80459171444519`) to the end of the trace reveals that the main thread spent **72.3%** of the time sleeping (`S`) and **27.6%** actively spinning on CPU (`Running`):

```sql
SELECT
  state,
  COUNT(*) AS cnt,
  SUM(dur) / 1e6 AS total_dur_ms,
  MIN(dur) / 1e6 AS min_dur_ms,
  MAX(dur) / 1e6 AS max_dur_ms
FROM thread_state
WHERE utid = 760 AND ts >= 80459171444519
GROUP BY state
ORDER BY total_dur_ms DESC;
```

| Thread State | Interval Count | Total Duration | Min Duration | Max Duration | Cause in Code |
| :--- | :--- | :--- | :--- | :--- | :--- |
| **`S` (Sleeping)** | `4` | **`6,703.18 ms`** | `700.78 ms` | `2,000.82 ms` | 4 `Thread.sleep()` calls in `performNetworkRequest()` |
| **`Running` (On CPU)** | `20` | **`2,559.81 ms`** | `0.00 ms` | `578.77 ms` | Busy-wait `while` loops in `cpuIntensiveComputation()` |
| **`R` (Runnable)** | `20` | **`2.11 ms`** | `0.01 ms` | `1.21 ms` | Scheduler wakeups and brief preemptions |

---

### 2.3 Phase-by-Phase Reconstruction (`thread_state` Intervals)

Querying individual `thread_state` intervals (`dur > 2 ms`) shows the exact sequence of CPU bursts and sleeps on the main thread:

```sql
SELECT
  ts,
  (ts - 80459171444519) / 1e6 AS ms_since_submit,
  dur / 1e6 AS dur_ms,
  state
FROM thread_state
WHERE utid = 760 AND ts >= 80459171444519 AND dur > 2e6
ORDER BY ts;
```

| Phase | Offset from Submit (`ms_since_submit`) | State | Duration (`dur_ms`) | Corresponding Code Execution |
| :--- | :--- | :--- | :--- | :--- |
| **1. Request Prep + Attempt #1 CPU** | `+0.63 ms` -> `+1,019.36 ms` | `Running` | **`1,018.68 ms`** *(across 5 slices)* | `prepareNetworkRequest()` (`1,000 ms` CPU) + Attempt #1 `cpuIntensiveComputation(20)` |
| **2. Network Attempt #1 (Timeout)** | `+1,019.36 ms` -> `+3,020.18 ms` | `S` (Sleep) | **`2,000.82 ms`** | `performNetworkRequest(2000)` -> `Thread.sleep(2000)` (`return false`) |
| **3. Network Attempt #2 (CPU)** | `+3,020.23 ms` -> `+3,040.24 ms` | `Running` | **`20.00 ms`** | Attempt #2 `cpuIntensiveComputation(20)` |
| **4. Network Attempt #2 (Timeout)** | `+3,040.24 ms` -> `+5,041.01 ms` | `S` (Sleep) | **`2,000.78 ms`** | `performNetworkRequest(2000)` -> `Thread.sleep(2000)` (`return false`) -- **5s input ANR threshold crossed** |
| **5. Network Attempt #3 (CPU)** | `+5,041.06 ms` -> `+5,061.30 ms` | `Running` | **`20.11 ms`** *(8.05 + 7.93 + 4.14 ms)* | Attempt #3 `cpuIntensiveComputation(20)` |
| **6. Network Attempt #3 (Timeout)** | `+5,061.30 ms` -> `+7,062.09 ms` | `S` (Sleep) | **`2,000.80 ms`** | `performNetworkRequest(2000)` -> `Thread.sleep(2000)` (`return false`) |
| **7. Network Attempt #4 (CPU)** | `+7,062.15 ms` -> `+7,082.38 ms` | `Running` | **`20.22 ms`** | Attempt #4 `cpuIntensiveComputation(20)` |
| **8. Network Attempt #4 (Success)** | `+7,082.38 ms` -> `+7,783.16 ms` | `S` (Sleep) | **`700.78 ms`** | `performNetworkRequest(2000)` hits `Math.random() < 0.2`, sleeps `~700 ms`, `return true` |
| **9. Handle Response (CPU)** | `+7,783.21 ms` -> `+9,281.30 ms` | `Running` | **`1,479.68 ms`** *(across 6 slices)* | `handleNetworkResponse()` (`Trace.beginSection("handleNetworkResponse")` at `+7,783.44 ms`) runs `cpuIntensiveComputation(2000)` until trace ends |

---

## 3. Code Mapping (`ProfilingManagerJavaSnippets.java`)

In `ProfilingManagerJavaSnippets.java` (lines `38` and `158-221`), the `OnClickListener` for `R.id.submit` runs `onClickSubmit()` directly on the main UI thread:

```java
private static final int NETWORK_TIMEOUT_MILLISECS = 2000;

public void setupButtonCallback() {
  findViewById(R.id.submit).setOnClickListener(submitButtonView -> {
    Trace.beginSection("MyApp:SubmitButton");
    onClickSubmit();
    Trace.endSection();
  });
}

public void onClickSubmit() {
  // 1. Blocks main thread on CPU for 1,000 ms
  prepareNetworkRequest();

  // 2. Synchronous retry loop on main thread (up to 10 attempts * 2,020 ms = 20.2 seconds!)
  boolean networkRequestSuccess = false;
  int maxAttempts = 10;
  while (!networkRequestSuccess && maxAttempts > 0) {
    networkRequestSuccess = performNetworkRequest(NETWORK_TIMEOUT_MILLISECS);
    maxAttempts--;
  }

  // 3. Blocks main thread on CPU for another 2,000 ms
  if (networkRequestSuccess) {
    handleNetworkResponse();
  }
}

boolean performNetworkRequest(int timeoutMilliseconds) {
  cpuIntensiveComputation(20);
  try {
    if (Math.random() < 0.2) {
      // Simulate performing a network request by waiting a random period of time
      int networkRequestTimeMs = (int) (Math.random() * timeoutMilliseconds);
      Thread.sleep(networkRequestTimeMs);
      return true;
    } else {
      // Simulate a timeout
      Thread.sleep(timeoutMilliseconds);
    }
  } catch (InterruptedException e) {
  }
  return false;
}

void cpuIntensiveComputation(int durationMs) {
  long start = System.currentTimeMillis();
  while (System.currentTimeMillis() - start < durationMs) {
  }
}

void prepareNetworkRequest() {
  cpuIntensiveComputation(1000);
}

public void handleNetworkResponse() {
  Trace.beginSection("handleNetworkResponse");
  cpuIntensiveComputation(2000);
  Trace.endSection();
}
```

---

## 4. Recommended Remediation

> **Tip:** Never perform network I/O, `Thread.sleep()`, or multi-hundred-millisecond CPU computations on the Android main UI thread.

1. **Offload `onClickSubmit()` to a Background Thread / Coroutine:**
   * In Java, dispatch `prepareNetworkRequest()`, the `performNetworkRequest()` retry loop, and heavy response processing in `handleNetworkResponse()` to a background `ExecutorService` (e.g., `Executors.newSingleThreadExecutor()`), then marshal only lightweight UI updates back to the main thread via `runOnUiThread(...)` or `View.post(...)`.
   * In Kotlin, use `lifecycleScope.launch(Dispatchers.IO)` (for network waiting) and `withContext(Dispatchers.Default)` (for CPU-intensive preparation/parsing).
2. **Use Non-Blocking / Asynchronous Retries with Backoff:**
   * Avoid holding threads with `Thread.sleep()` inside tight retry loops; use asynchronous HTTP client timeouts/retries or `WorkManager` for deferrable background network tasks.