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singleInstance

import { singleInstance } from "@tynd/core/client";

Cross-OS exclusive lock + argv/cwd forwarding.

acquire(id): Promise<SingleInstanceResult>

interface SingleInstanceResult {
  acquired: boolean;
  already:  boolean;   // true if another instance currently holds the lock
}
 
const { acquired, already } = await singleInstance.acquire("com.example.myapp");
if (!acquired) {
  // Duplicate launch. The primary has already been focused and notified.
  process.exit(0);
}
  • id — stable reverse-DNS identifier. Doubles as the OS lock name and the local socket name.
  • When acquired: false, already: true means a peer instance is running. Both fields coincide for the typical case; already exists to distinguish “lock unavailable for some other reason” when debugging.

isAcquired(): Promise<boolean>

Whether this process currently holds the lock.

if (await singleInstance.isAcquired()) { /* we're the primary */ }

onSecondLaunch(handler): () => void

Fires in the primary instance whenever a duplicate launch is detected.

interface SecondLaunchPayload {
  argv: string[];   // duplicate's argv (argv[0] is the exe path)
  cwd:  string;
}
 
singleInstance.onSecondLaunch(({ argv, cwd }) => {
  console.log("reopened with", argv.slice(1), "at", cwd);
});

onOpenUrl(handler): () => void

Fires when the app is opened via a registered URL scheme (declared in tynd.config.ts::protocols). Fires both on cold start (argv has the URL) and on duplicate launch.

singleInstance.onOpenUrl((url) => {
  // url = "myapp://invite/abc123"
  const parsed = new URL(url);
  router.navigate(parsed.pathname);
});

Backing mechanisms

  • Windows — named pipe (\\.\pipe\<id>) + the single-instance lock for the lock.
  • Linux — abstract socket + kernel-managed lock. Auto-released on process exit.
  • macOS — CFMessagePort + Mach-kernel-backed port.

Argv/cwd forwarding uses the local socket library for the local socket — one JSON line, then close.

Reserved schemes

When declaring protocols: ["myapp"] in tynd.config.ts, these schemes are rejected at config-validation time:

http, https, file, ftp, mailto, javascript, data, about, blob, tynd, tynd-bin

Notes

  • Use a stable id — don’t include the version. Users upgrading need the old version to auto-focus before it shuts down.
  • acquire() should be called before rendering any UI or starting background work. The return value determines the entire process lifecycle.
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