PhpFileCacheEngine

Each entry is a PHP file (<?php return [...];), read with include. With OPcache, an entry is read from memory, not from the disk: a value of scalars and arrays is written as PHP code, which OPcache keeps in shared memory with nothing to decode, and any other value (an object) is written serialized.

<?php
$cache = new \ByJG\Cache\Psr16\PhpFileCacheEngine(
    'config',      // The start of the file names (default: 'cache')
    '/var/cache'   // The directory (default: the system temp dir); it must exist
);
$cache->set('key', ['a' => 1]);

When to use it

For entries written once and read on every request: a DI container (byjg/config's withCache()), compiled data, a configuration. A web request (PHP-FPM) reads them from OPcache instead of opening and unserializing a file.

Not for values that change often (sessions, query results, counters): each write compiles the file again, and OPcache keeps the previous version as wasted memory until it restarts (opcache.max_wasted_percentage), which empties the whole OPcache at once. Use FileSystemCacheEngine, RedisCacheEngine or MemcachedEngine for those.

Details

• Files readable by their owner only (0600): an entry can hold secrets (a cached configuration has the passwords). The user that reads the cache (PHP-FPM) must be the one that writes it.
• Never read half written: a file is written to a temporary file and renamed, then invalidated in OPcache (opcache_invalidate()), so a change is seen even with opcache.validate_timestamps=0.
• TTL: an expired entry is removed when it is read. There is no garbage collector nor atomic operation.
• A null value removes the entry, as FileSystemCacheEngine does.
• isAvailable() is false when the directory does not exist or cannot be written.