robobun
e7672b2d04
Add string fast path for postMessage and structuredClone ( #21926 )
...
## Summary
Implements a string fast path optimization for `postMessage` and
`structuredClone` operations that provides significant performance
improvements for string-only data transfer, along with various bug fixes
and infrastructure improvements.
## Key Performance Improvements
**postMessage with Workers:**
- **Small strings (11 chars):** ~5% faster (572ns vs 599ns)
- **Medium strings (14KB):** **~2.7x faster** (528ns vs 1.40μs)
- **Large strings (3MB):** **~660x faster** (540ns vs 356μs)
**Compared to Node.js postMessage:**
- Similar performance for small strings
- Competitive for medium strings
- **~455x faster** for large strings (540ns vs 245μs)
## Implementation Details
The optimization adds a **string fast path** that bypasses full
structured cloning serialization when:
- Input is a pure string (`value.isString()`)
- No transfer list or message ports are involved
- Not being stored persistently
### Core Changes
**String Thread-Safety Utilities (`BunString.cpp/h`):**
- `isCrossThreadShareable()` - Checks if string can be safely shared
across threads
- `toCrossThreadShareable()` - Converts strings to thread-safe form via
`isolatedCopy()`
- Handles edge cases: atoms, symbols, substring slices, external buffers
**Serialization Fast Path (`SerializedScriptValue.cpp`):**
- New `m_fastPathString` field stores string data directly
- Bypasses full object serialization machinery for pure strings
- Creates isolated copies for cross-thread safety
**Deserialization Fast Path:**
- Directly returns JSString from stored string data
- Avoids parsing serialized byte streams
**Updated Flags System (`JSValue.zig`, `Serialization.cpp`):**
- Replaces boolean `forTransfer` with structured `SerializedFlags`
- Supports `forCrossProcessTransfer` and `forStorage` distinctions
**Structured Clone Infrastructure:**
- Moved `structuredClone` implementation to dedicated
`StructuredClone.cpp`
- Added `jsFunctionStructuredCloneAdvanced` for testing with custom
flags
- Improved class serialization compatibility checks (`isForTransfer`,
`isForStorage`)
**IPC Improvements (`ipc.zig`):**
- Fixed race conditions in `SendQueue` by deferring cleanup to next tick
- Proper fd ownership handling with `bun.take()`
- Cached IPC serialize/parse functions for better performance
**BlockList Thread Safety Fixes (`BlockList.zig`):**
- Fixed potential deadlocks by moving mutex locking inside methods
- Added atomic `estimated_size` counter to avoid lock during GC
- Corrected pointer handling in comparison functions
- Improved GC safety in `rules()` method
## Benchmark Results
```
❯ bun-21926 bench/string-postmessage.mjs # This branch
postMessage(11 chars string) 572.24 ns/iter
postMessage(14 KB string) 527.55 ns/iter ← ~2.7x faster
postMessage(3 MB string) 539.70 ns/iter ← ~660x faster
❯ bun-1.2.20 bench/string-postmessage.mjs # Previous
postMessage(11 chars string) 598.76 ns/iter
postMessage(14 KB string) 1.40 µs/iter
postMessage(3 MB string) 356.38 µs/iter
❯ node bench/string-postmessage.mjs # Node.js comparison
postMessage(11 chars string) 569.63 ns/iter
postMessage(14 KB string) 1.46 µs/iter
postMessage(3 MB string) 245.46 µs/iter
```
**Key insight:** The fast path achieves **constant time performance**
regardless of string size (~540ns), while traditional serialization
scales linearly with data size.
## Test Coverage
**New Tests:**
- `test/js/web/structured-clone-fastpath.test.ts` - Fast path memory
usage validation
- `test/js/web/workers/structuredClone-classes.test.ts` - Comprehensive
class serialization tests
- Tests ArrayBuffer transferability
- Tests BunFile cloning with storage/transfer restrictions
- Tests net.BlockList cloning behavior
- Validates different serialization contexts (default, worker, window)
**Enhanced Tests:**
- `test/js/web/workers/structured-clone.test.ts` - Multi-function
testing
- Tests `structuredClone`, `jscSerializeRoundtrip`, and cross-process
serialization
- Validates consistency across different serialization paths
- `test/js/node/cluster.test.ts` - Better error handling and debugging
**Benchmarks:**
- `bench/string-postmessage.mjs` - Worker postMessage performance
comparison
- `bench/string-fastpath.mjs` - Fast path vs traditional serialization
comparison
## Bug Fixes
**BlockList Threading Issues:**
- Fixed potential deadlocks when multiple threads access BlockList
simultaneously
- Moved mutex locks inside methods rather than holding across entire
function calls
- Added atomic size tracking for GC compatibility
- Fixed comparison function pointer handling
**IPC Race Conditions:**
- Fixed race condition where `SendQueue._onAfterIPCClosed()` could be
called on wrong thread
- Deferred cleanup operations to next tick using task queue
- Improved file descriptor ownership with proper `bun.take()` usage
**Structured Clone Compatibility:**
- Enhanced class serialization with proper transfer/storage mode
checking
- Fixed edge cases where non-transferable objects were incorrectly
handled
- Added better error reporting for unsupported clone operations
## Technical Notes
- Thread safety ensured via `String.isolatedCopy()` for cross-VM
transfers
- Memory cost calculation updated to account for string references
- Maintains full compatibility with existing structured clone semantics
- Does not affect object serialization or transfer lists
- Proper cleanup and error handling throughout IPC pipeline
---------
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com >
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Meghan Denny <meghan@bun.sh >
2025-08-20 00:25:00 -07:00
