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@bpcreech
bpcreech committed May 26, 2024
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139 changes: 74 additions & 65 deletions content/post/mini-racer-v0.12.2.md
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Expand Up @@ -177,77 +177,86 @@ such calls are ignored.

Here's roughly what the system looks like:

<center><div style="max-width: 300px;">

```goat
+----------------------------------------+
| |
| (Python) MiniRacer user code |
| MiniRacer user code |
| |
| +----------------------+ |
| | | |
| | my_callback_func | |
| | | |
| +------------+---------+ |
| 3 | ^ |
+----------------------------|---|-------+
1 | | |
v | |
+----------------------------|---|-------+
| | | |
| (Python) MiniRacer | | |
| | | |
| +--------------------------|---|-----+ |
| | | | | |
| | (Python) _Context | | | |
| | v | 10 | |
| +----------+-----------+ |
| 3 | ^ |
+--------------------------|-----|-------+
1 | | |
v | |
+--------------------------|-----|-------+
| | | |
| MiniRacer | | |
| | | |
| +------------------------|-----|-----+ |
| | | | | |
| | _Context | | | |
| | v | 10 | |
| | +----------------------------+---+ | |
| | | | | |
| | | _CallbackRegistry | | |
| | | | | |
| | +------------------------+-------+ | |
| | 4 | ^ | |
| +---------------+----------|---|-----+ |
| 2 | | | |
+-----------------|----------|---|-------+
| | |
v | |
+----------------------------|---|-----------------------------------------+
| (C++) MiniRacer::Context | | |
| | | |
| v | |
| +------------------------------|---+ +-------------------------------+ |
| | | | | 5 | |
| | (C++) MiniRacer | +-------+ (C++) v8::Isolate | |
| | ::JSCallbackMaker 9 | | | v | |
| | +----------------------------+-+ | | +---------------------------+ | |
| | | | | | | | | |
| | | (C++) | | | | v8::Function | | |
| | | MiniRacer::CallbackCaller | | | | | | |
| | | | | | | | | |
| | +------------------------------+ | | | | | |
| | ^ | | | | | |
| +------------------------------|---+ | | +----------------------+ | | |
| | 8 | | | | | | |
| +-----------------------+---+ | | | (data) | | | |
| | | | | | v8::Array | | | |
| | (C++) |<----+ | [callback_id, | | | |
| | MiniRacer | 7 | | | callback_caller_id] | | | |
| | ::JSCallbackMaker | | | | | | | |
| | ::OnCalledStatic | | | +----------------------+ | | |
| | | | | | | |
| +---------------------------+ | +---------------------------+ | |
| | ^ | |
| | | 6 | |
| | +------------+--------------+ | |
| | | | | |
| | | JavaScript code | | |
| | | | | |
| | +---------------------------+ | |
| | | |
| +-------------------------------+ |
| |
+--------------------------------------------------------------------------+
| | +----------------------+---------+ | |
| | 4 | ^ | |
| +---------------+--------|-----|-----+ |
| 2 | | | |
+-----------------|--------|-----|-------+
| | |
Python space | | |
··················|········|·····|································
C++ space | | |
v | |
+--------------------------|-----|-----+
| MiniRacer::Context | | |
| | | |
| v | |
| +------------------------------|---+ |
| | | | | +---------------------+
| | MiniRacer::JSCallbackMaker | | | | |
| | 9 | | | | (C++) |
| | +----------------------------+-+ | | | MiniRacer |
| | | | | | | ::JSCallbackMaker |
| | | MiniRacer::CallbackCaller |<------+ ::OnCalledStatic |
| | | | | | 8 | |
| | +------------------------------+ | | +---------------------+
| | | | ^
| +------------------------+---------+ +--------------|----------+
| 5 | | |
| +------------------------|--------------------------|--------+ |
| | | | | |
| | v8::Isolate | 7 | | |
| | | | | |
| | | +-----------------------+------+ | |
| | | | | | |
| | `->| v8::Function | | |
| | | | | |
| | | data: | | |
| | | +--------------------------+ | | |
| | +-----------------+ | | | | | |
| | | | 6 | | v8::Array | | | |
| | | JavaScript code |------>| | [callback_id, | | | |
| | | | | | callback_caller_id] | | | |
| | +-----------------+ | | | | | |
| | | +--------------------------+ | | |
| | | | | |
| | +------------------------------+ | |
| | | |
| +------------------------------------------------------------+ |
| |
+----------------------------------------------------------------+
```

</div></center>

1. MiniRacer Python user code instantiates a `py_mini_racer.MiniRacer` object
which contains a `py_mini_racer._Context` object.

Expand All @@ -259,9 +268,9 @@ Here's roughly what the system looks like:

3. MiniRacer Python user code passes Python function `my_callback_func` into
`MiniRacer.wrap_py_function`. `MiniRacer` stores a wrapper of
`my_callback_func` in its `_CallbackRegistry`, thus generating a callback ID.
`my_callback_func` in its `_CallbackRegistry`, thus generating a `callback_id`.

4. `MiniRacer.wrap_py_function` passes this callback ID down to the C++ side of
4. `MiniRacer.wrap_py_function` passes this `callback_id` down to the C++ side of
the house to generate a V8 callback function.

5. `MiniRacer::JSCallbackMaker` creates a `v8::Function` within the
Expand All @@ -279,14 +288,14 @@ Here's roughly what the system looks like:

8. `MiniRacer::JSCallbackMaker::OnCalledStatic` digs out the
`[callback_id, callback_caller_id]` array to find the
`MiniRacer::CallbackCaller`, and the context-specific callback ID to pass
`MiniRacer::CallbackCaller`, and the `callback_id` to pass
back to it.

9. `MiniRacer::CallbackCaller` converts the returned V8 value to a
`MiniRacer::BinaryValue`, and calls back to the Python C function pointer
with that and the callback ID.
with that and the `callback_id`.

10. The `MiniRacer._ContextRegistry` converts the callback ID to the destination
10. The `MiniRacer._ContextRegistry` converts the `callback_id` to the destination
Python function object (`my_callback_func`), and finally passes the function
parameters back to it.

Expand Down Expand Up @@ -348,12 +357,12 @@ This rule seems obvious in restrospect! But it's hard to implement. I:

### Breaking up the Python code

As of `v0.7.0` PyMiniRacer was basically a single file, 519 lines of code.
As of `v0.7.0` PyMiniRacer was basically a single Python file, 519 lines of code.

As of `v0.11.1` that file was up to 1,355 lines of code. This was quickly
As of `v0.11.1` that Python file was up to 1,355 lines of code. This was quickly
growing beyond manageability!

So I split it up. The largest file is now 473 LoC.
So I split it up. The largest Python file is now 473 LoC.

Splitting up code is always an exercise in breaking the code down into component
parts, drawing out a DAG (hopefully acyclic!), and lumping things back together
Expand Down

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