PHP opcache_jit_blacklist() Function: Usage and Examples

Marks a callable to be excluded from future tracing-JIT compilation.

What It Does and When to Use It

Blacklist a first-class callable before exercising it. OPcache caches compiled opcodes, JIT may optimize CPU-intensive PHP, while APCu caches application-owned values.

Requirements, Inputs and Expected Behavior

Confirm the runtime, extension, environment variables, and permissions before running the examples in production. PHP 8.4+; already JIT-compiled sections are not retroactively deoptimized.

Example 1: Basic Operation

Blacklist a first-class callable before exercising it.

<?php
function sumNumbers(int $n): int {
     return array_sum(range(1, $n));
 }
 opcache_jit_blacklist(sumNumbers(...));
 echo sumNumbers(6);

Example 2: Behavior and Validation

An anonymous Closure can also be excluded from future tracing JIT.

<?php
$callback = static function (int $value): int { return $value * 2; };
 opcache_jit_blacklist($callback);
 echo $callback(7);

Practical Example: Application Use

Guard a feature introduced in PHP 8.4 when maintaining multi-version code.

<?php
if (function_exists('opcache_jit_blacklist')) {
     $transform = static fn (string $s): string => trim($s);
     opcache_jit_blacklist($transform);
     echo $transform(' checked ');
 }

Important Behavior and Edge Cases

The second example highlights: An anonymous Closure can also be excluded from future tracing JIT. The practical example adds: Guard a feature introduced in PHP 8.4 when maintaining multi-version code.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Marks a callable to be excluded from future tracing-JIT compilation.
• Guard a feature introduced in PHP 8.4 when maintaining multi-version code.
• Profile application response times and memory under representative traffic before tuning.