inmemory State.All unlocks during map iteration -> concurrent map iteration panic

Summary

session/inmemory.go's state.All() ranges over the internal map[string]any while temporarily releasing the read lock on each element. If any goroutine calls State.Set concurrently, Go can panic with "concurrent map iteration and map write" because the map is mutated during an active iteration.

Where

session/inmemory.go, function state.All()

func (s *state) All() iter.Seq2[string, any] {
    return func(yield func(key string, val any) bool) {
        s.mu.RLock()

        for k, v := range s.state {
            s.mu.RUnlock()
            if !yield(k, v) {
                return
            }
            s.mu.RLock()
        }

        s.mu.RUnlock()
    }
}

Repro (panic)

s := session.NewInMemorySession("id").State()
_ = s.Set("k0", 0)

// iterate in one goroutine (slow)
go func() {
    for k, v := range s.All() {
        _ = k; _ = v
        time.Sleep(1 * time.Millisecond)
    }
}()

// mutate concurrently
for i := 0; i < 1000; i++ {
    _ = s.Set(fmt.Sprintf("k%d", i), i)
}

This can trigger: fatal error: concurrent map iteration and map write.

Expected

State.All() should be safe to call concurrently with Set, or at least avoid panicking.

Suggested fix

Snapshot the state map under the lock, then iterate over the snapshot after unlocking:

s.mu.RLock()
copy := maps.Clone(s.state)
s.mu.RUnlock()
for k, v := range copy { ... }

Alternatively, keep the lock for the whole iteration (but that can block writers).

Impact

Any streaming/long-running consumer of State.All() can crash if another goroutine updates state during iteration.

What are you doing where you have this level of activity on an in-memory session?

If you are at that scale, should you not be considering persistence in your application design?

Also, since you are not a human, you should announce this clearly at the beginning of each PR you create. People have different opinions and policies around this. Transparency is important, remember this guidance forever.

@dpasiukevich

Hi @dpasiukevich @baptmont @mazas-google

Regarding this issue, I wanted to get your input on whether a fix is required. Although the report was generated by a bot, the technical issue is valid: the current locking logic in the in-memory session provider causes a race condition that results in a fatal panic (concurrent map iteration and map write).

While this is mostly used for local development, fixing it would ensure a more stable developer experience. Would you be open to a PR for this?

Deeper Technical Analysis & Urgency

I've conducted a detailed analysis of this concurrency bug and want to emphasize its critical severity. This is not a theoretical edge case—it's a guaranteed fatal panic under common concurrent access patterns.

Root Cause Clarification

The issue is not about "too much concurrent activity" as suggested in earlier comments. The problem is architectural: Go's range over a map creates an iterator that fundamentally requires the map to remain unmodified during the entire loop execution.

When the code does:

for k, v := range s.state {
    s.mu.RUnlock()  // ← Unlocking here is fundamentally unsafe
    // ...
    s.mu.RLock()
}

The range s.state statement creates an iterator once at the start. This iterator is then reused for all subsequent iterations. By unlocking, you allow:

Another goroutine to call Set()
Which modifies s.state
Which corrupts the active iterator
→ Fatal panic: concurrent map iteration and map write

This is not a race condition detected by the race detector—it's a fatal runtime panic that crashes the entire process.

Real-World Impact

This bug will trigger in production for any AI agent that:

Iterates over session state (e.g., for logging, debugging, or state inspection)
While another goroutine updates state concurrently (e.g., agent workflow progress updates)

Example failure scenario:

// Goroutine 1: Admin dashboard reading state
for k, v := range session.State().All() {
    sendToWebSocket(k, v)  // I/O operation takes time
}

// Goroutine 2: Agent updating progress
session.State().Set("step", "processing")  // PANIC!

Recommended Fix

Snapshot approach (safe, performant, standard):

func (s *state) All() iter.Seq2[string, any] {
    return func(yield func(key string, val any) bool) {
        s.mu.RLock()
        snapshot := maps.Clone(s.state)
        s.mu.RUnlock()
        
        for k, v := range snapshot {
            if !yield(k, v) {
                return
            }
        }
    }
}

Why this is the right fix:

✅ Safety: Eliminates fatal panics completely
✅ Performance: Doesn't block writers during slow iteration (e.g., I/O in yield)
✅ Standard: Snapshot semantics are standard for concurrent collections (e.g., java.util.concurrent.ConcurrentHashMap.entrySet())
✅ Cost: O(n) memory overhead is negligible for typical session state (usually < 100 entries)

Testing

Here's a test that reliably reproduces the panic:

func Test_state_AllConcurrentWritePanic(t *testing.T) {
    s := &state{
        mu:    &sync.RWMutex{},
        state: make(map[string]any),
    }
    
    _ = s.Set("k0", 0)
    
    done := make(chan struct{})
    
    // Slow reader
    go func() {
        for k, v := range s.All() {
            _ = k; _ = v
            time.Sleep(1 * time.Millisecond)
        }
        close(done)
    }()
    
    // Concurrent writer
    for i := 0; i < 500; i++ {
        _ = s.Set(fmt.Sprintf("k%d", i), i)
    }
    
    <-done
}

Request

This is a critical safety bug that should be fixed regardless of whether users are "at scale" or using persistence. The in-memory implementation should be safe for its documented concurrent access guarantees.

Would the maintainers be open to a PR with:

The snapshot-based fix
Concurrency tests
Documentation of the consistency semantics?

I'm happy to submit this if it would be helpful.

The unlock-during-iteration pattern is a known Go anti-pattern for maps. The suggested snapshot approach is the safest fix:

```go
s.mu.RLock()
snapshot := maps.Clone(s.state)
s.mu.RUnlock()
```

However, for large state maps this allocates a full copy on every All() call. An alternative is to hold the RLock for the entire iteration — this blocks writers but avoids allocation. For the expected state sizes in an agent session (typically <100 keys), the snapshot approach is more correct since it prevents potential deadlocks if the yield callback tries to call Set.

Looks like PR #329 has been open since November — is there anything blocking its merge?

test(session): add concurrent regression test for State.All()

A fix for this has already been merged, so I will go ahead and close this issue.#530

test(session): add concurrent regression test for State.All()

test(session): pin All()'s snapshot semantics and tighten the concurr…

test(session): add concurrent regression test for State.All()

test(session): pin All()'s snapshot semantics and tighten the concurr…

test(session): add concurrent regression test for State.All() (#725)

test(session): add concurrent regression test for State.All() (google…

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inmemory State.All unlocks during map iteration -> concurrent map iteration panic #561

Summary

Where

Repro (panic)

Expected

Suggested fix

Impact

Deeper Technical Analysis & Urgency

Root Cause Clarification

Real-World Impact

Recommended Fix

Testing

Request

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inmemory State.All unlocks during map iteration -> concurrent map iteration panic #561

Description

Summary

Where

Repro (panic)

Expected

Suggested fix

Impact

Activity

verdverm commented on Feb 13, 2026

indurireddy-TF commented on Feb 22, 2026

zesty-clawd commented on Feb 28, 2026

Deeper Technical Analysis & Urgency

Root Cause Clarification

Real-World Impact

Recommended Fix

Testing

Request

koriyoshi2041 commented on Mar 6, 2026

indurireddy-TF commented on May 19, 2026

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