How do we resolve race conditions?
Published: 2024-06-25 09:42:55

When dealing with race conditions in saving drafts, the main challenge is ensuring that updates are applied in the correct order. This is especially important if multiple updates (like auto-saving drafts) are happening concurrently. Here’s how you can handle such situations:

### 1. **Using Versioning**
One effective approach is to use versioning to ensure that only the latest update is applied.

```javascript
let currentVersion = 0;

async function saveDraft(draft, version) {
  if (version < currentVersion) {
    console.log("Outdated version, ignoring the save");
    return;
  }

  // Simulate async save operation
  await new Promise(resolve => setTimeout(resolve, 100));

  if (version >= currentVersion) {
    // Update current version
    currentVersion = version;
    console.log("Draft saved:", draft);
  }
}

// Example usage
async function updateDraft(draft) {
  const version = ++currentVersion;
  await saveDraft(draft, version);
}

updateDraft("Draft 1");
updateDraft("Draft 2"); // Only "Draft 2" should be saved
```

### 2. **Queueing Updates**
Queue updates to ensure that only one update happens at a time.

```javascript
class UpdateQueue {
  constructor() {
    this.queue = [];
    this.processing = false;
  }

  async enqueue(updateFn) {
    this.queue.push(updateFn);
    if (!this.processing) {
      this.processing = true;
      while (this.queue.length > 0) {
        const fn = this.queue.shift();
        await fn();
      }
      this.processing = false;
    }
  }
}

const updateQueue = new UpdateQueue();

async function saveDraft(draft) {
  await new Promise(resolve => setTimeout(resolve, 100)); // Simulate async save
  console.log("Draft saved:", draft);
}

// Example usage
updateQueue.enqueue(() => saveDraft("Draft 1"));
updateQueue.enqueue(() => saveDraft("Draft 2")); // Ensures "Draft 2" is saved after "Draft 1"
```

### 3. **Debouncing Updates**
Debouncing can help by ensuring that updates are not too frequent, which can mitigate race conditions.

```javascript
function debounce(fn, delay) {
  let timeout;
  return (...args) => {
    clearTimeout(timeout);
    timeout = setTimeout(() => fn(...args), delay);
  };
}

async function saveDraft(draft) {
  await new Promise(resolve => setTimeout(resolve, 100)); // Simulate async save
  console.log("Draft saved:", draft);
}

const debouncedSaveDraft = debounce(saveDraft, 300);

// Example usage
debouncedSaveDraft("Draft 1");
debouncedSaveDraft("Draft 2"); // Only "Draft 2" will be saved
```

### 4. **Using a Mutex**
A mutex ensures that only one update can occur at a time.

```javascript
class Mutex {
  constructor() {
    this.queue = Promise.resolve();
  }

  lock() {
    let unlockNext;
    const willLock = new Promise(resolve => unlockNext = resolve);
    const willUnlock = this.queue.then(() => unlockNext);
    this.queue = willLock;
    return willUnlock;
  }
}

const mutex = new Mutex();

async function saveDraft(draft) {
  const unlock = await mutex.lock();
  try {
    await new Promise(resolve => setTimeout(resolve, 100)); // Simulate async save
    console.log("Draft saved:", draft);
  } finally {
    unlock();
  }
}

// Example usage
saveDraft("Draft 1");
saveDraft("Draft 2"); // Ensures only one draft is saved at a time
```

### 5. **Atomic Operations with IndexedDB (Advanced)**
For complex scenarios, using a client-side database like IndexedDB to manage drafts can ensure atomicity.

```javascript
// Initialize IndexedDB
let db;
const request = indexedDB.open("DraftDB", 1);

request.onupgradeneeded = event => {
  db = event.target.result;
  db.createObjectStore("drafts", { keyPath: "id" });
};

request.onsuccess = event => {
  db = event.target.result;
};

async function saveDraft(draft) {
  return new Promise((resolve, reject) => {
    const transaction = db.transaction(["drafts"], "readwrite");
    const store = transaction.objectStore("drafts");
    const request = store.put(draft);

    request.onsuccess = () => {
      console.log("Draft saved:", draft);
      resolve();
    };

    request.onerror = event => {
      console.error("Draft save failed", event);
      reject();
    };
  });
}

// Example usage
saveDraft({ id: 1, content: "Draft 1" });
saveDraft({ id: 1, content: "Draft 2" }); // Ensures the latest draft is saved
```

Each of these methods can help manage race conditions when saving drafts by ensuring that updates are applied in the correct order or frequency. The choice of method depends on the specific requirements and complexity of your application.