SweepStore/dart/lib/concurrency.dart

import 'dart:io';
import 'dart:isolate';
import 'dart:math';

import 'package:sweepstore/header.dart';
import 'package:sweepstore/helpers.dart';
import 'package:sweepstore/structures.dart';

int _randomId() {
  // mix timestamp with random for better uniquness
  // keep it positive to avoid signed int issues when storing
  int time = DateTime.now().millisecondsSinceEpoch32();
  int random = Random().nextInt(0x80000000);
  return (time ^ random) & 0x7FFFFFFF;
}

// Spawn a ticket for a worker to perform an operation
void spawnTicket(RandomAccessFile file, {
  required SweepstoreTicketOperation operation,
  required int keyHash,
  required int writeSize,
  required void Function() onApproved,
  String? debugLabel,
}) {

  void log(String message) {

    String prefix = debugLabel != null ? "\x1B[38;5;208m[Ticket Spawner - $debugLabel]:\x1B[0m " : "\x1B[38;5;208m[Ticket Spawner]:\x1B[0m ";
    // print("$prefix$message");

  }
  void tickSleep([int microsecondVariance = 10]) {
    preciseSleep(Duration(microseconds: 100 + Random().nextInt(microsecondVariance)));
  }
  Map<String, int> expSleepTracker = {};
  void expSleep(String label) {
    int count = expSleepTracker[label] ?? 0;
    int sleepTime = (1 << count); // Exponential backoff
    // sleepTime = max(1, min(sleepTime, 1000)); // Clamp between 1ms and 1000ms
    preciseSleep(Duration(microseconds: sleepTime * 1000));
    expSleepTracker[label] = count + 1;
  }

  // Reduce the chance of race conditions by adding a small random delay
  tickSleep(100);

  SweepstoreHeader header = SweepstoreHeader(file);
  SweepstoreConcurrencyHeader concurrencyHeader = SweepstoreConcurrencyHeader(header);

  int? ticketIndex;
  int myIdentifier = _randomId();

  // Try to acquire a ticket - (Acquire loop)
  while (ticketIndex == null) {

    for (int i = 0; i < concurrencyHeader.numberOfWorkers; i++) {

      SweepstoreWorkerTicket ticket = concurrencyHeader[i];

      if (!ticket.writable()) {
        continue;
      }

      int identifier = ticket.identifier;

      bool identifier_unassigned = identifier == 0;
      bool stale_heartbeat = (DateTime.now().millisecondsSinceEpoch32() - ticket.workerHeartbeat) > 2000;
      bool is_free = ticket.ticketState == SweepstoreTicketState.FREE;

      if (identifier_unassigned && stale_heartbeat && is_free) {
        ticket.write(
          identifier: myIdentifier,
          ticketState: SweepstoreTicketState.WAITING,
        );
        ticketIndex = i;
        log("Acquired ticket $ticketIndex with identifier $myIdentifier.");
        break;

      }

    }

    expSleep("acquire_loop");


    // Ensure we still own the ticket - if not, reset and try again
    if (ticketIndex != null) {
      SweepstoreWorkerTicket ticket = concurrencyHeader[ticketIndex];
      if (ticket.identifier != myIdentifier) {
        log("Lost ticket $ticketIndex, retrying...");
        ticketIndex = null;
      }
    }
  }

  // We have a ticket, set it up
  SweepstoreWorkerTicket myTicket = concurrencyHeader[ticketIndex];
  myTicket.write(
    workerHeartbeat: DateTime.now().millisecondsSinceEpoch32(),
    ticketState: SweepstoreTicketState.WAITING,
    ticketOperation: operation,
    keyHash: keyHash,
    writeSize: writeSize,
  );

  // Wait for approval - (Approval loop)
  while (true) {

    // Check we still own the ticket
    if (myTicket.identifier != myIdentifier) {
      String exceptionMessage = "CRITICAL: Lost ownership of ticket $ticketIndex, was expecting identifier $myIdentifier but found ${myTicket.identifier}.";
      throw Exception(exceptionMessage);
    }

    if (myTicket.ticketState == SweepstoreTicketState.APPROVED) {
      myTicket.write(
        ticketState: SweepstoreTicketState.EXECUTING,
      );
      onApproved();
      myTicket.write(
        ticketState: SweepstoreTicketState.COMPLETED,
      );

      break;
    }

    // randomSleep(10);
    tickSleep();

    // Update heartbeat
    if (DateTime.now().millisecondsSinceEpoch32() != myTicket.workerHeartbeat) {
      myTicket.write(
        workerHeartbeat: myTicket.workerHeartbeat,
      );
    }
  }



}

// Master side
void initialiseMasterListener(RandomAccessFile file) async {
  String filePath = file.path;
  Isolate.spawn((_) {

    void log(String message) {
      // print("\x1B[38;5;82m[Master Listener]:\x1B[0m $message");
    }

    RandomAccessFile file = File(filePath).openSync(mode: FileMode.append);

    SweepstoreHeader header = SweepstoreHeader(file);
    SweepstoreConcurrencyHeader concurrencyHeader = SweepstoreConcurrencyHeader(header);

    while (true) {

      for (int i = 0; i < concurrencyHeader.numberOfWorkers; i++) {

        SweepstoreWorkerTicket ticket = concurrencyHeader[i];

        if (ticket.ticketState == SweepstoreTicketState.WAITING) {
          log("Found waiting ticket $i (Key Hash: ${ticket.keyHash})...");

          // Approve the ticket
          ticket.write(
            ticketState: SweepstoreTicketState.APPROVED,
          );
          log("Approved ticket $i.");
        } else if (ticket.ticketState == SweepstoreTicketState.COMPLETED) {
          log("Ticket $i completed. Resetting ticket...");
          // Reset the ticket
          ticket.write(
            identifier: 0,
            workerHeartbeat: 0,
            ticketState: SweepstoreTicketState.FREE,
            ticketOperation: SweepstoreTicketOperation.NONE,
            keyHash: 0,
            writeSize: 0,
          );
          log("Reset ticket $i.");
        }

      }

      preciseSleep(Duration(milliseconds: 1));

    }
  }, null);
}