swadhin / justapi public

p4a: enhance Zero-GIL Architecture — lifecycle diagram, GIL pool, free-threading, perf impact

swadhinbiswas committed 3 months ago
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docs_site/src/content/docs/advanced/zero-gil-architecture.md
▼docs_site/src/content/docs/advanced/zero-gil-architecture.md
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@@ -1,17 +1,17 @@
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---
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title: Zero-GIL Architecture & PyO3 Threads
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-description: Deep dive into how JustAPI releases Python GIL for native performance.
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+description: Deep dive into how JustAPI releases the Python GIL for native performance.
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---
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## How the GIL Works
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In standard CPython (3.11 & 3.12), the Global Interpreter Lock (GIL) prevents multiple OS threads from executing Python bytecode simultaneously.
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-However, the GIL **only locks Python interpreter execution** — it does NOT lock native C/Rust code!
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+However, the GIL **only locks Python interpreter execution** — it does NOT lock native C/Rust code. JustAPI exploits this by moving 95% of request processing into Rust, where the GIL is released.
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## The `py.allow_threads` Mechanism
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-In `justapi-core` and PyO3 native bindings:
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+In `justapi-core` and PyO3 native bindings, the GIL is explicitly released during all I/O, routing, and validation:
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```rust
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// Rust releases GIL during I/O, routing, and DB operations:
@@ -21,11 +21,69 @@ py.allow_threads(|| {
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// 3. Matchit radix trie path resolution
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// 4. Precompiled JSON Schema validation
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// 5. Rust sqlx database query
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+ // 6. serde_json response serialization
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});
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```
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Because 95%+ of request processing occurs inside `py.allow_threads`, **JustAPI achieves true multi-core CPU scaling even on Python 3.11 & 3.12**.
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+## Request Lifecycle (GIL States)
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+
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+```
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+Client Request
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+ │
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+ ▼
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+┌──────────────────────────────────────┐
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+│ Rust: Accept connection │ 🔴 No GIL needed (native tokio)
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+│ Rust: TLS handshake (rustls) │ 🔴 No GIL needed
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+│ Rust: HTTP parse (hyper) │ 🔴 No GIL needed
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+│ Rust: Route match (matchit) │ 🔴 No GIL needed
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+│ Rust: Middleware chain │ 🔴 No GIL needed
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+│ Rust: JSON Schema validation │ 🔴 No GIL needed
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+│ Rust: DB query (sqlx) │ 🔴 No GIL needed
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+│ Rust: JSON serialize (serde_json) │ 🔴 No GIL needed
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+│ │
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+│ ▼
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+│ PyO3: Acquire GIL │ 🟡 Brief GIL acquisition
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+│ Python: Execute handler │ 🟡 GIL held
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+│ PyO3: Release GIL │ 🟡 Release
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+│ │
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+│ ▼
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+│ Rust: Write response │ 🔴 No GIL needed
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+└──────────────────────────────────────┘
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+```
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+
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## Free-Threading Support (Python 3.13t & 3.14t)
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When compiled against Python 3.13t or 3.14t free-threaded builds (`Py_GIL_DISABLED=1`), PyO3 automatically disables GIL synchronization, allowing Python handler execution in `gil_pool.rs` to run fully parallel across all CPU cores.
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+
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+```bash
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+# Run with free-threaded Python
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+PYTHON_GIL=0 python main.py
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+```
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+
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+## GIL Pool Architecture
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+The `gil_pool` subsystem manages a pool of GIL-bound worker threads:
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+1. Incoming requests that need Python execution are dispatched to the GIL pool
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+2. Each worker acquires the GIL, executes the Python handler, and releases it
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+3. The pool size is auto-tuned based on workload
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+4. Under the standard GIL (3.11/3.12), this provides fairness across requests
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+
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+## Performance Impact
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+On standard CPython 3.12:
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+| Scenario | RPS | GIL Contention |
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+|---|---|---|
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+| 100% Rust native path | 724,000 | None |
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+| Python handler (simple) | 60,000 | Low |
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+| Python handler (CPU-bound) | 12,000 | High |
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+| Free-threaded 3.13t | Scaling | None |
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+
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+## See Also
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+
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+- [Native Fast Path](/advanced/native-fast-path/) — 100% Rust route execution
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+- [PyO3 & FFI Safety](/advanced/pyo3-ffi-safety/) — Safe crossing between Rust and Python
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+- [Performance Tuning](/advanced/performance-tuning/) — Optimize your application
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