Concurrency

A Manager owns one pkl server process and multiplexes every evaluator over it. Starting the server is the slowest step of an evaluation, so create one manager and share it.

What is thread-safe

• Any thread may call createEvaluator, evaluate, and close on a shared manager at any time.
• Any thread may evaluate through any evaluator, including several threads through the same evaluator at once. Requests carry ids and their responses are matched independently, so a slow evaluation does not hold up a fast one.
• Evaluator.close is idempotent. It waits for the evaluator's reader and logger callbacks, then tells the server.
• Manager.deinit must run once, after your threads stop starting requests. It cancels requests still pending and waits for callbacks to finish.

const shared = try manager.createEvaluator(zig_pkl.Options.restricted(), &rejected);
defer shared.close();

var workers: [4]std.Thread = undefined;
for (&workers, 0..) |*worker, index| {
    worker.* = try std.Thread.spawn(.{}, work, .{ shared, index });
}
for (workers) |worker| worker.join();

See examples/concurrency.

Inside the manager

One response thread reads frames from the server and wakes the request each one answers. Log messages are delivered on that thread. Reader callbacks go to a bounded pool of worker threads that start on demand; see Readers.

Failure

A broken pipe, a server exit, or a malformed frame is terminal for the manager. Every pending request fails with that error, later requests fail immediately with it, and Manager.failure() returns it. Create a new manager to recover. See Errors.