Here are a few question-based article titles that fit the content you provided: * Why Are My Parallel AJAX Requests Stalling, and How Can I Fix It? * Parallel AJAX Requests: How to Avoid Session Blo

Parallel AJAX Requests: Unlocking Concurrent Operation

Simultaneous AJAX requests are crucial for enhancing user experience and data flow within web applications. However, facing issues where these requests stall or interfere with each other can be frustrating. In this scenario, the challenge lies in two AJAX requests not running concurrently, leading to a noticeable delay in progress updates.

Identifying the Cause

The root of the problem often lies in server-side settings or specific implementation details. In this case, the culprit appears to be a session blocking issue. By default, PHP employs file-based sessions, which introduces a lock mechanism to prevent simultaneous access to session data during writes.

This locking mechanism ensures data integrity, but it also creates a bottleneck. When multiple AJAX requests originating from the same page try to modify the session, they encounter the lock and must wait for the first request to complete its operation. Consequently, the progress updates are delayed until the initial export script finishes.

Solution: Disable File-Based Sessions or Use session_write_close()

To overcome this issue and enable true parallelism, two approaches can be taken:

1. Disable File-Based Sessions: Configure PHP to store session data in a different backend, such as a database or Memcached, which supports concurrent access.
2. Use session_write_close(): If file-based sessions are a requirement, use the session_write_close() function explicitly to release the lock after writing to the session. This allows subsequent requests to proceed without waiting for the session file to be re-opened and unlocked.

By implementing either of these solutions, the concurrent AJAX requests will be freed from the blocking behavior, allowing them to update progress independently and provide a smoother user experience.

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