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Why does batch() cause nested signal deadlock and how to fix it?

March 18, 2026

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batch() defers signal reads during execution to batch change detection, causing nested computed() signals to miss updates and create deadlocks. Signals read inside batch don't trigger dependents until batch completes, leading to stale values or infinite loops.

Root Cause: Angular intentionally blocks signal propagation during batch() for performance, breaking nested reactivity patterns.

Solutions:

  1. untracked() for safe reads inside batch
  2. Multiple sequential batches for complex updates
  3. Restructure to top-level signals only

Step-by-Step Guide: Fix Batch() Nested Signal Deadlock:-

Step 1: Identify the Problem:-

Code

// PROBLEM: This creates deadlock
batch(() => {
  this.items.update(items => [...items, { price: 15 }]);     // Signal A
  this.discount.set(0.15);                                  // Signal B
  // total() computed signal MISSES discount update!
});

Step 2: Understand Root Cause:-

Code

batch() defers ALL signal reads → computed() caches stale values
Signal A update → Signal B update → computed() still sees OLD Signal B
Result: Infinite loop or frozen UI

Step 3:-Choose Your Fix (3 Options):-

Option A: untracked() - Quick Fix:-

Code

// Step 3A: Wrap nested reads
total = computed(() => {
  const subtotal = untracked(() => 
    this.items().reduce((sum, i) => sum + i.price, 0)  // Ignores batch deferral
  );
  return subtotal * (1 - this.discount());
});

Option B:-Sequential Batches - Recommended

Code

// Step 3B: Split into multiple batches
addItem() {
  // Batch 1: Items only
  batch(() => this.items.update(items => [...items, { price: 15 }]));
  
  // Batch 2: Discount (total() recomputes immediately)
  batch(() => this.discount.set(0.15));
}

Option C:-Restructure Signals - Best Long-term

Code

// Step 3C: Top-level signals only
items = signal([]);
discount = signal(0.1);
subtotal = computed(() => this.items().reduce((sum, i) => sum + i.price, 0));
total = computed(() => this.subtotal() * (1 - this.discount())); // No nesting!

Step 4: Test the Fix:-

Code

// Add this test
it('batch updates work correctly', () => {
  component.addItem();
  expect(component.total()).toBe(41.25); // 10+20+15 * 0.85
});

Step 5: Production Checklist:-

Code

No signal reads inside batch() computations
untracked() used for nested dependencies  
Sequential batches for complex updates
DevTools signal graph shows correct dependencies
Performance budget passes (no infinite loops)
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Why does batch() cause nested signal deadlock and how to fix it?

batch() defers signal reads during execution to batch change detection, causing nested computed() signals to miss updates and create deadlocks. Signals read inside batch don't trigger dependents until batch completes, leading to stale values or infinite loops.

Root Cause: Angular intentionally blocks signal propagation during batch() for performance, breaking nested reactivity patterns.

Solutions:

  1. untracked() for safe reads inside batch
  2. Multiple sequential batches for complex updates
  3. Restructure to top-level signals only

Step-by-Step Guide: Fix Batch() Nested Signal Deadlock:-

Step 1: Identify the Problem:-

Code

// PROBLEM: This creates deadlock
batch(() => {
  this.items.update(items => [...items, { price: 15 }]);     // Signal A
  this.discount.set(0.15);                                  // Signal B
  // total() computed signal MISSES discount update!
});

Step 2: Understand Root Cause:-

Code

batch() defers ALL signal reads → computed() caches stale values
Signal A update → Signal B update → computed() still sees OLD Signal B
Result: Infinite loop or frozen UI

Step 3:-Choose Your Fix (3 Options):-

Option A: untracked() - Quick Fix:-

Code

// Step 3A: Wrap nested reads
total = computed(() => {
  const subtotal = untracked(() => 
    this.items().reduce((sum, i) => sum + i.price, 0)  // Ignores batch deferral
  );
  return subtotal * (1 - this.discount());
});

Option B:-Sequential Batches - Recommended

Code

// Step 3B: Split into multiple batches
addItem() {
  // Batch 1: Items only
  batch(() => this.items.update(items => [...items, { price: 15 }]));
  
  // Batch 2: Discount (total() recomputes immediately)
  batch(() => this.discount.set(0.15));
}

Option C:-Restructure Signals - Best Long-term

Code

// Step 3C: Top-level signals only
items = signal([]);
discount = signal(0.1);
subtotal = computed(() => this.items().reduce((sum, i) => sum + i.price, 0));
total = computed(() => this.subtotal() * (1 - this.discount())); // No nesting!

Step 4: Test the Fix:-

Code

// Add this test
it('batch updates work correctly', () => {
  component.addItem();
  expect(component.total()).toBe(41.25); // 10+20+15 * 0.85
});

Step 5: Production Checklist:-

Code

No signal reads inside batch() computations
untracked() used for nested dependencies  
Sequential batches for complex updates
DevTools signal graph shows correct dependencies
Performance budget passes (no infinite loops)