Improve App Launch Speed: Defer Disk Scanning

by Alex Johnson 46 views

In today's fast-paced digital world, app launch speed is crucial for user satisfaction. A sluggish app can lead to frustration and abandonment. This article delves into a common problem: slow app launch times caused by disk scanning during initialization. We'll explore a practical solution – deferring disk scanning until the user initiates it – and discuss the implementation details, benefits, and considerations.

The Problem: Slow Launch Times Due to Disk Scanning

Many applications perform a full filesystem scan during the app's initialization phase. This process, often occurring within the __init__ method or a similar startup function, can significantly delay the app's launch. In the provided example, the Disk Sweeper Pro application suffers from this issue. The GUI performs a complete filesystem scan during initialization (__init__ → _rebuild_model() → collect()), causing the app to take several seconds to open. This creates a poor user experience characterized by:

  • Users seeing nothing while the app scans in the background.
  • Lack of feedback on the ongoing process.
  • The app appearing frozen or slow to launch.
  • Inability to cancel or control the initial scan.
# mainwindow.py:95-102
def __init__(self):
 super().__init__()
 self.setWindowTitle("Disk Sweeper Pro")
 self.setWindowIcon(QIcon(":/icons/logo"))
 QApplication.setStyle("Fusion")

 # This blocks startup while scanning filesystem
 self._rebuild_model() # ← BLOCKS HERE

# mainwindow.py:184-187
def _rebuild_model(self):
 rows = collect(rules_mod.RULES, include=set(rules_mod.SEVERITY_ORDER)) # ← SLOW
 rows.sort(key=lambda c: (rules_mod.SEVERITY_ORDER[c.rule.severity], -c.size))
 self.model = CandidateModel(rows)

This initial disk scanning process, while intended to prepare the app for use, can inadvertently create a negative first impression. Users are accustomed to near-instantaneous app launches, and any delay can lead to impatience and a perception of poor performance. Therefore, optimizing the launch speed by addressing this disk scanning bottleneck is paramount for a positive user experience.

The Solution: Defer Disk Scanning to User Initiation

The proposed solution is to launch the app immediately with an empty table and a prominent "Scan" button. This approach shifts the disk scanning process from the app's initialization to a user-initiated action. By deferring the scan, the app can launch quickly, providing users with immediate access to the interface. The user can then click the "Scan" button to start the analysis process when they are ready.

User Experience Flow

  1. Instant App Launch: The app window appears immediately, presenting an empty table.
  2. Prominent "Scan" Button: A clear and visible "Scan for Cleanup Candidates" button is displayed.
  3. User-Initiated Scan: The user clicks the "Scan" button to begin the scanning process.
  4. Progress Display: A progress dialog or indicator informs the user about the scanning progress.
  5. Results Population: Once the scan is complete, the results populate the table, allowing the user to review and clean.

This user-initiated approach provides a more controlled and transparent experience. Users are not kept waiting during the launch process and have a clear understanding of when and why the scanning is occurring.

Implementation Approaches

Several implementation options can be considered, each with its own trade-offs:

  • Option A: Simple Synchronous with Progress Dialog: This approach involves showing the window immediately with an empty model, adding a "Scan" button, displaying a progress dialog when the button is clicked, running the scan synchronously, and updating the table upon completion. This is the simplest approach to implement but can still block the UI thread during the scan.
  • Option B: Threaded Background Scan (Recommended): This option, which is the recommended approach, shows the window immediately, adds a "Scan" button, runs the scan in a background thread (using QThread in this example), displays a progress bar or spinner, allows for cancellation of the scan, and updates the table upon completion. This approach provides the best user experience by preventing the UI from freezing during the scan.
  • Option C: Auto-Scan with Delay: This approach shows the window immediately and starts the scan automatically after a short delay (e.g., 500ms). A progress indicator is displayed to inform the user about the ongoing scan. While this approach automates the scan, it might not be suitable for all users, as some may prefer to initiate the scan manually.

Option B (threaded) provides the best balance between performance and user experience, particularly the ability to cancel the scan if needed. This flexibility is crucial for handling large filesystems or situations where the user needs to interrupt the process.

Technical Changes Required

Implementing the deferred disk scanning solution requires several technical modifications to the application's code.

1. Modify __init__ to Skip Initial Scan

The __init__ method needs to be modified to initialize the app with an empty model instead of performing the scan during startup.

def __init__(self):
 super().__init__()
 self.setWindowTitle("Disk Sweeper Pro")
 self.setWindowIcon(QIcon(":/icons/logo"))
 QApplication.setStyle("Fusion")

 # Initialize with empty model instead of scanning
 self.model = CandidateModel([]) # Empty list

 # ... rest of UI setup ...

This change ensures that the app launches quickly without the initial delay caused by the disk scan.

2. Add "Scan" Button to UI

A "Scan" button needs to be added to the UI to allow users to initiate the scanning process manually. This button should be prominently displayed and clearly labeled.

# Add to button bar or make it prominent
btn_scan = QPushButton(" Scan for Cleanup Candidates")
btn_scan.setIcon(QIcon(":/icons/search")) # or appropriate icon
btn_scan.clicked.connect(self._start_scan)

The button's click event should be connected to a new function that handles the scanning logic.

3. Implement Scanning Logic

The scanning logic needs to be implemented in a separate function that is called when the "Scan" button is clicked. This function should handle the display of a progress dialog and the execution of the scan.

@Slot()
def _start_scan(self):
 # Option A: Simple synchronous
 progress = QProgressDialog("Scanning filesystem...", "Cancel", 0, 0, self)
 progress.setWindowModality(Qt.WindowModal)
 progress.show()
 QApplication.processEvents()

 self._rebuild_model()
 self.table.setModel(self.model)
 self._update()
 progress.close()

 # Option B: Threaded (requires QThread implementation)
 # self.scan_thread = ScanThread(rules_mod.RULES)
 # self.scan_thread.finished.connect(self._on_scan_complete)
 # self.scan_thread.start()

As shown in the code snippet, both synchronous (Option A) and threaded (Option B) approaches are possible. The threaded approach is recommended for a smoother user experience.

4. Update Existing "Reload Rules" to Use Same Pattern

The existing _reload_rules() function can be updated to reuse the same scanning mechanism, ensuring consistency and efficiency.

These technical changes, while requiring some effort, are crucial for achieving the desired improvement in app launch speed and user experience.

Benefits of Deferring Disk Scanning

Deferring disk scanning offers several significant benefits:

  • ✅ Instant app launch: The window appears immediately, providing a faster and more responsive experience.
  • ✅ User control: Users decide when to initiate the scan, giving them more control over the process.
  • ✅ Better feedback: A progress dialog shows what's happening during the scan, providing transparency and reassurance.
  • ✅ Cancellation: With threading, users can abort long scans if needed, preventing unnecessary delays.
  • ✅ Reduced perceived lag: The app feels much faster, even if the scan takes the same amount of time overall.
  • ✅ Better for repeated use: Users can re-scan on demand, allowing for more flexible usage.

These benefits collectively contribute to a more positive and efficient user experience.

Considerations for Implementation

While deferring disk scanning offers numerous advantages, there are several considerations to keep in mind during implementation.

Threading Safety

If using QThread, ensure the collect() function is thread-safe (the example uses pathlib and shutil, which are generally thread-safe). Use signals and slots for updating the UI from the thread and handle thread cleanup properly to avoid resource leaks.

State Management

Disable the "Clean" button until the scan completes to prevent unintended actions. Show a "Scanning..." state in the UI to provide clear feedback to the user. Also, handle the "Reload Rules" functionality during an active scan to avoid conflicts.

User Expectations

Some users may expect auto-scan on launch. Consider adding a "Scan automatically on launch" checkbox in the settings for future enhancement to cater to different user preferences.

Addressing these considerations ensures a robust and user-friendly implementation of the deferred disk scanning solution.

Testing Checklist

A thorough testing checklist is essential to ensure the solution works as expected.

  • [ ] App window opens instantly (< 500ms).
  • [ ] Scan button is prominent and clear.
  • [ ] Progress dialog appears during the scan.
  • [ ] Table populates correctly after the scan.
  • [ ] "Clean" button is disabled before the scan.
  • [ ] Can run multiple scans (re-scan).
  • [ ] "Reload Rules" triggers a new scan.
  • [ ] (If threaded) Can cancel scan mid-operation.

This checklist covers the key aspects of the implementation and helps identify any potential issues.

Priority and Effort Estimate

This improvement is considered High priority due to its significant impact on user experience. The effort estimate varies depending on the chosen implementation approach:

  • Option A (Simple): Low - 2-3 hours
  • Option B (Threaded): Medium - 4-6 hours including testing

The threaded approach, while requiring more effort, is recommended for its superior user experience.

Related Future Enhancements

This improvement also enables several future enhancements:

  • Auto-scan on launch setting
  • Scheduled/timed scans
  • Watch mode (continuous monitoring)
  • Incremental scanning

These enhancements can further improve the app's functionality and user experience.

Conclusion

Deferring disk scanning until user initiation is a practical solution to improve app launch speed and enhance user experience. By implementing this approach, applications can launch quickly, provide users with more control, and offer better feedback during the scanning process. The threaded implementation (Option B) is recommended for its ability to allow scan cancellation and prevent UI freezing. By addressing this issue, developers can create more responsive and user-friendly applications. For further reading on optimizing application performance, check out Performance Optimization on Android Developers.