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PHP
Singleton Trait
A reusable trait that turns any class into a lazily-instantiated singleton with a single ::instance() accessor. Throws on clone/wakeup to prevent accidental duplication.
@admin
Bash
flock — Cron-Singleton Lock
Prevent two copies of a cron job from running simultaneously. flock takes an FD to a lock file; if the lock is held, the second invocation exits immediately.
Go
sync.Once — Lazy One-Time Initialization
Run a function exactly once, even from many goroutines. Standard pattern for lazy singletons, expensive setup, and one-time configuration.
Kotlin
object Declaration — Singleton
`object` declares a thread-safe lazy singleton. Built into the language — no `private constructor + getInstance()` boilerplate. Also: anonymous `object : Interface { … }` for one-shot instances.
Java
Singleton via enum
`enum` with a single value is the simplest correct singleton implementation: lazy, thread-safe, serialization-safe, reflection-safe. Joshua Bloch's recommendation in Effective Java.