Add atomic cache-based mutex lock to prevent concurrent import cron execution by Claude · Pull Request #1198 · Codeinwp/feedzy-rss-feeds

Claude · 2026-03-23T14:55:19Z

WordPress pseudo-cron can fire the same scheduled event multiple times during overlapping page loads. Without synchronization, concurrent execution of the same import job causes duplicate posts (TOCTOU race in duplicate detection) and resource waste.

Changes

Added per-job mutex locking in run_cron() at includes/admin/feedzy-rss-feeds-import.php:1545-1608:

Atomic lock acquisition

Uses wp_cache_add() for atomic lock acquisition (returns false if lock already exists)
Prevents race condition where two processes could both acquire the lock
Lock stored in feedzy_import_locks cache group with key feedzy_import_lock_{job_id}

Dynamic lock TTL

TTL calculated from feedzy_max_execution_time filter (default 500s) + 60s buffer
Prevents lock expiration while import is still running
Filterable via feedzy_import_lock_ttl hook for customization
Falls back to 300s (5 minutes) if max execution time is unlimited or not set

Lock cleanup

Release in finally block via wp_cache_delete() to guarantee cleanup on both success and error paths
Auto-expires based on dynamic TTL as safety net

Error handling

Catches Throwable instead of Exception to handle PHP 8+ TypeError/Error
Makes cron execution more resilient

Logging

Skipped jobs logged at INFO level with job title, ID, and skip reason
Uses non-translatable strings for internal logging

Example

foreach ( $feedzy_imports as $job ) {
    $lock_key = 'feedzy_import_lock_' . $job->ID;
    
    // Calculate dynamic TTL
    $max_execution_time = (int) apply_filters( 'feedzy_max_execution_time', 500 );
    if ( $max_execution_time <= 0 ) {
        $max_execution_time = 300;
    }
    $lock_ttl = (int) apply_filters( 'feedzy_import_lock_ttl', $max_execution_time + 60, $job );
    
    // Atomic lock acquisition
    if ( ! wp_cache_add( $lock_key, time(), 'feedzy_import_locks', $lock_ttl ) ) {
        // Log skip and continue
        continue;
    }
    
    try {
        $this->run_job( $job, $max );
        // ... existing logic
    } catch ( Throwable $e ) {
        // Handle all errors
    } finally {
        wp_cache_delete( $lock_key, 'feedzy_import_locks' );
    }
}

Behavior

Same job cannot run concurrently (atomic lock prevents race conditions)
Different jobs run in parallel (job-specific locks)
Lock always released via finally block
Dynamic TTL prevents lock expiration during long-running imports
Catches all PHP errors including TypeError for PHP 8+ compatibility

[!WARNING]

Original prompt

This section details on the original issue you should resolve

<filter_complete></filter_complete>

<issue_title>Add transient-based mutex lock to prevent concurrent import cron execution</issue_title>
<issue_description>## Problem

WordPress pseudo-cron can fire the same scheduled event multiple times if page loads overlap. Without a lock, the same import job can run concurrently, causing duplicate posts (TOCTOU race condition in duplicate detection) and wasted server resources.

Solution

import.php — In run_cron(), add a per-job transient lock:

Before each job: check get_transient('feedzy_import_lock_' . $job->ID), skip if active
Set transient with 10-minute TTL before running the job
Use finally { delete_transient($lock_key); } to ensure cleanup on both success and error
Log skipped jobs for debugging

Files Affected

includes/admin/feedzy-rss-feeds-import.php

Acceptance Criteria

Same import job cannot run concurrently
Lock is always released after job completes (success or error)
Skipped jobs are logged with job title and ID
Different import jobs can still run in parallel
Lock expires after 10 minutes even if cleanup fails (safety net)

Priority: High — prevents duplicate imported posts
Regression risk: Low — worst case a job is skipped once, retries on next cron cycle</issue_description>

Comments on the Issue (you are @claude[agent] in this section)

Original prompt

This section details on the original issue you should resolve

<issue_title>Add transient-based mutex lock to prevent concurrent import cron execution</issue_title>
<issue_description>## Problem

WordPress pseudo-cron can fire the same scheduled event multiple times if page loads overlap. Without a lock, the same import job can run concurrently, causing duplicate posts (TOCTOU race condition in duplicate detection) and wasted server resources.

Solution

import.php — In run_cron(), add a per-job transient lock:

Before each job: check get_transient('feedzy_import_lock_' . $job->ID), skip if active

Set transient with 10-minute TTL before running the job

Use finally { delete_transient($lock_key); } to ensure cleanup on both success and error

Log skipped jobs for debugging

Files Affected

includes/admin/feedzy-rss-feeds-import.php

Acceptance Criteria

Same import job cannot run concurrently

Lock is always released after job completes (success or error)

Skipped jobs are logged with job title and ID

Different import jobs can still run in parallel

Lock expires after 10 minutes even if cleanup fails (safety net)

Priority: High — prevents duplicate imported posts
Regression risk: Low — worst case a job is skipped once, retries on next cron cycle</issue_description>

Comments on the Issue (you are @claude[agent] in this section)

Fixes Add transient-based mutex lock to prevent concurrent import cron execution #1197

…ution Co-authored-by: ineagu <1849868+ineagu@users.noreply.github.com> Agent-Logs-Url: https://github.com/Codeinwp/feedzy-rss-feeds/sessions/e881eaf6-2715-40de-8539-35fc0bd118cf

pirate-bot · 2026-03-23T15:44:18Z

🌍 i18n String Review Report

📊 Summary

Category	Count
➕ Added	1
➖ Removed	0
🔄 Changed	0
Total	1

➕ Added Strings (1) - Click to expand

String	Location	Words	Suggested Match
Skipping job "%1$s" (ID: %2$d) - already run...	includes/admin/feedzy-rss...	8	No close match
Total		8

Copilot

Pull request overview

Adds a per-import-job mutex in the import cron runner to reduce duplicate imports caused by overlapping WP-Cron executions.

Changes:

Introduces a per-job transient lock key (feedzy_import_lock_{job_id}) to skip already-running jobs.
Adds INFO logging when a job is skipped due to an existing lock.
Ensures lock cleanup via a finally block after each job run.

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Copilot · 2026-03-23T15:45:20Z

+			// Set lock with 10-minute TTL
+			set_transient( $lock_key, time(), 10 * MINUTE_IN_SECONDS );


The lock TTL is hard-coded to 10 minutes. This can expire while an import is still running (run_job() increases max execution time via the feedzy_max_execution_time filter), which would allow a second cron execution to acquire the lock and run concurrently. Suggest basing the TTL on the configured max execution time (plus a buffer) and/or making it filterable so longer-running imports don’t lose the lock mid-run.

Suggested change

// Set lock with 10-minute TTL

set_transient( $lock_key, time(), 10 * MINUTE_IN_SECONDS );

// Determine lock TTL based on max execution time (plus buffer) and allow filtering.

$max_execution_time = (int) apply_filters( 'feedzy_max_execution_time', ini_get( 'max_execution_time' ) );

if ( $max_execution_time <= 0 ) {

$max_execution_time = 300; // Fallback to 5 minutes if unlimited or not set.

}

$lock_ttl = (int) apply_filters( 'feedzy_import_lock_ttl', $max_execution_time + 60, $job );

set_transient( $lock_key, time(), $lock_ttl );

Copilot · 2026-03-23T15:45:21Z

 						'error'  => $e->getMessage(),
 					)
 				);
+			} finally {
+				// Always release the lock, even on error
+				delete_transient( $lock_key );


This block still only catches Exception; PHP Errors/TypeErrors (Throwable) during imports would bypass the catch/logging and can abort cron processing. Consider switching the catch to Throwable (and logging it) to make cron execution more resilient and failures visible.

Copilot · 2026-03-23T15:45:21Z

+			// Check if job is already running
+			if ( get_transient( $lock_key ) ) {
+				Feedzy_Rss_Feeds_Log::info(
+					// translators: %1$s is the import job title, %2$d is the job ID.
+					sprintf( __( 'Skipping job "%1$s" (ID: %2$d) - already running', 'feedzy-rss-feeds' ), $job->post_title, $job->ID ),
+					array(
+						'job_id' => $job->ID,
+						'reason' => 'concurrent_execution_prevented',
+					)
+				);
+				continue;
+			}
+
+			// Set lock with 10-minute TTL
+			set_transient( $lock_key, time(), 10 * MINUTE_IN_SECONDS );


The lock acquisition uses a non-atomic check-then-set (get_transient() followed by set_transient()). Two overlapping requests can both see no transient and then both set it, so the same job can still run concurrently (the exact race this lock is meant to prevent). Consider switching to an atomic primitive for acquisition (e.g., add_option() with a unique option name, or a cache add/"add"-semantics call) and only proceed when acquisition succeeds.

ineagu · 2026-03-23T16:09:16Z

@claude[agent] can you fix the errors and avoid creating strings?

…able, remove i18n string Co-authored-by: ineagu <1849868+ineagu@users.noreply.github.com> Agent-Logs-Url: https://github.com/Codeinwp/feedzy-rss-feeds/sessions/0a2662a5-9f58-44a8-ad51-bd8821fe85d6

Claude · 2026-03-23T16:11:28Z

@claude[agent] can you fix the errors and avoid creating strings?

Fixed in dc5c7d1:

Removed i18n string - Changed from translatable string to simple concatenation for internal logging
Atomic lock acquisition - Replaced non-atomic get/set pattern with wp_cache_add() which returns false if lock exists
Dynamic TTL - Lock duration now based on feedzy_max_execution_time filter (500s default) + 60s buffer, filterable via feedzy_import_lock_ttl
Catch Throwable - Changed from Exception to Throwable for PHP 8+ TypeError/Error handling

Initial plan

da1934c

Claude AI assigned Claude and ineagu Mar 23, 2026

Claude started work on behalf of ineagu March 23, 2026 14:55 View session

Add transient-based mutex lock to prevent concurrent import cron exec…

4a64b3d

…ution Co-authored-by: ineagu <1849868+ineagu@users.noreply.github.com> Agent-Logs-Url: https://github.com/Codeinwp/feedzy-rss-feeds/sessions/e881eaf6-2715-40de-8539-35fc0bd118cf

Claude AI changed the title ~~[WIP] Add transient-based mutex lock to prevent concurrent import execution~~ Add transient-based mutex lock to prevent concurrent import cron execution Mar 23, 2026

Claude AI requested a review from ineagu March 23, 2026 15:10

Claude finished work on behalf of ineagu March 23, 2026 15:10

ineagu requested a review from Copilot March 23, 2026 15:41

Copilot started reviewing on behalf of ineagu March 23, 2026 15:42 View session

Copilot AI reviewed Mar 23, 2026

View reviewed changes

Claude started work on behalf of ineagu March 23, 2026 16:09 View session

Fix lock mechanism: use atomic wp_cache_add, dynamic TTL, catch Throw…

dc5c7d1

…able, remove i18n string Co-authored-by: ineagu <1849868+ineagu@users.noreply.github.com> Agent-Logs-Url: https://github.com/Codeinwp/feedzy-rss-feeds/sessions/0a2662a5-9f58-44a8-ad51-bd8821fe85d6

Claude AI changed the title ~~Add transient-based mutex lock to prevent concurrent import cron execution~~ Add atomic cache-based mutex lock to prevent concurrent import cron execution Mar 23, 2026

Claude finished work on behalf of ineagu March 23, 2026 16:12

ineagu closed this Mar 24, 2026

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Add atomic cache-based mutex lock to prevent concurrent import cron execution#1198

Add atomic cache-based mutex lock to prevent concurrent import cron execution#1198
Claude wants to merge 3 commits intomasterfrom
claude/add-transient-mutex-lock

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		// Set lock with 10-minute TTL
		set_transient( $lock_key, time(), 10 * MINUTE_IN_SECONDS );

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