Parallel Worker Pool for VlConverter + V8 Platform Init Safety

.github/workflows/CI.yml

@@ -485,6 +485,12 @@ jobs:
         run: pixi run dev-py
       - name: Run tests
         run: pixi run test-py
+      - name: Upload failed images
+        uses: actions/upload-artifact@v6
+        if: failure()
+        with:
+          name: failed-images-python-${{ matrix.options[0] }}
+          path: vl-convert-python/tests/failed/
 
   # Build and test aarch64 Linux wheel using manylinux container
   vl-convert-python-tests-linux-aarch64:

Cargo.toml

@@ -20,6 +20,7 @@ codegen-units = 1
 [workspace.dependencies]
 anyhow = "1.0"
 assert_cmd = "2.0"
+backon = { version = "1", default-features = false, features = ["tokio-sleep", "std"] }
 clap = { version = "4.5", features = ["derive"] }
 
 # Deno dependencies - versions correspond to Deno v2.6.6

vl-convert-python/README.md

@@ -91,6 +91,22 @@ vg_spec = vlc.vegalite_to_vega(chart.to_json(), vl_version="4.17")
 with open("altair_chart.vg.json", "wt") as f:
     json.dump(vg_spec, f)
 ```
+
+## Configure Worker Parallelism
+By default, `vl-convert-python` uses `1` converter worker. You can configure this globally:
+
+```python
+import vl_convert as vlc
+
+vlc.get_num_workers()   # 1
+vlc.set_num_workers(4)  # enable parallel worker pool
+vlc.warm_up_workers()   # optional: pre-initialize workers before first conversion
+```
+
+This setting applies to subsequent conversions and enables parallel work across Python threads.
+Calling `warm_up_workers()` is optional and only needed if you want to avoid first-request
+worker startup latency.
+
 # How it works
 This crate uses [PyO3](https://pyo3.rs/) to wrap the [`vl-convert-rs`](https://crates.io/crates/vl-convert-rs) Rust crate as a Python library. The `vl-convert-rs` crate is a self-contained Rust library for converting [Vega-Lite](https://vega.github.io/vega-lite/) visualization specifications into various formats.  The conversions are performed using the Vega-Lite and Vega JavaScript libraries running in a v8 JavaScript runtime provided by the [`deno_runtime`](https://crates.io/crates/deno_runtime) crate.  Font metrics and SVG-to-PNG conversions are provided by the [`resvg`](https://crates.io/crates/resvg) crate.