mirror of
https://github.com/pocketpy/pocketpy
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42 lines
977 B
Markdown
42 lines
977 B
Markdown
---
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icon: dot
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label: 'Miscellaneous'
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order: 0
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---
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## The scope lock of gc
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Sometimes you need to use the following code to prevent the gc from collecting objects.
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```cpp
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auto _lock = vm->heap.gc_scope_lock();
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```
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The scope lock is required if you create a PyObject and then try to run python-level bytecodes.
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For example, you create a temporary object on the stack and then call `vm->py_next`.
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```cpp
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void some_func(VM* vm){
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PyObject* obj = VAR(List(5));
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// unsafe
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PyObject iter = vm->py_iter(obj);
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PyObject next = vm->py_next(iter);
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}
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```
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Because users can have an overload of `__next__`, this call is unsafe.
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When the vm is running python-level bytecodes, gc may start and delete your temporary object.
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The scope lock prevents this from happening.
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```cpp
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void some_func(VM* vm){
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PyObject* obj = VAR(List(5));
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// safe
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auto _lock = vm->heap.gc_scope_lock();
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PyObject iter = vm->py_iter(obj);
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PyObject next = vm->py_next(iter);
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}
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```
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