atomics-sync/es/once.js

JavaScript multithreading synchronization library

const { compareExchange, store } = Atomics;
/**
 * A synchronization primitive that ensures a function is executed only once,
 * even when called from multiple threads.
 * Uses atomic operations for thread-safe execution tracking.
 */
export class Once {
    /**
     * Initializes a new Once primitive in shared memory
     * @returns A new Int32Array backed by SharedArrayBuffer initialized to NOT_EXECUTED
     */
    static init() {
        const once = new Int32Array(new SharedArrayBuffer(Int32Array.BYTES_PER_ELEMENT));
        store(once, Once.INDEX_EXECUTED, Once.EXECUTED_NO);
        return once;
    }
    /**
     * Executes the provided function exactly once, even if called from multiple threads
     * @param once The Once primitive to use for synchronization
     * @param fn The function to execute (will be called at most once)
     * @remarks The function will be called by whichever thread wins the atomic race
     */
    static execute(once, fn) {
        if (compareExchange(once, Once.INDEX_EXECUTED, Once.EXECUTED_NO, Once.EXECUTED_YES) === Once.EXECUTED_NO) {
            fn();
        }
    }
    /**
     * Checks if the function has been executed
     * @param once The Once primitive to check
     * @returns true if the function has been executed, false otherwise
     */
    static isExecuted(once) {
        return Atomics.load(once, Once.INDEX_EXECUTED) === Once.EXECUTED_YES;
    }
}
// Index for the execution state in the shared array
Once.INDEX_EXECUTED = 0;
// Possible execution states
Once.EXECUTED_NO = 0; // Function has not been executed
Once.EXECUTED_YES = 1; // Function has been executed
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