Switch from heap/stack to just a heap #1069
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fitzgen
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This commit switches strategies for storing `JsValue` from a heap/stack to just one heap. This mirrors the new strategy for `JsValue` storage in rustwasm#1002 and should make multiplexing those strategies at `wasm-bindgen`-time much easier. Instead of having one array which acts as a stack for borrowed values and one array for a heap of borrowed values, only one JS array is used for storage of JS values now. This makes `getObject` far simpler by simply being an array access, but it means that cloning an object now reserves a new slot instead of reference counting it. If the old reference counting behavior is needed it's thought that `Rc<JsValue>` can be used in Rust. The new "heap" has an initial stack pointer which grows downwards, and a heap which grows upwards. The heap is a singly-linked-list which is allocated/deallocated from. The stack grows downwards to zero and presumably starts generating errors once it underflows. An initial stack size of 32 is chosen as that should encompass all use cases today, but we can eventually probably add configuration for this! Note that the heap is initialized to all `null` for the stack and then the initial JS values (`undefined`, `null`, `true`, `false`) are pushed onto the heap in reserved locations.
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Oops right! I've updated the internal contributing documentation to reflect this change |
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This commit switches strategies for storing
JsValuefrom a heap/stackto just one heap. This mirrors the new strategy for
JsValuestoragein #1002 and should make multiplexing those strategies at
wasm-bindgen-time much easier.Instead of having one array which acts as a stack for borrowed values
and one array for a heap of borrowed values, only one JS array is used
for storage of JS values now. This makes
getObjectfar simpler bysimply being an array access, but it means that cloning an object now
reserves a new slot instead of reference counting it. If the old
reference counting behavior is needed it's thought that
Rc<JsValue>can be used in Rust.
The new "heap" has an initial stack pointer which grows downwards, and a
heap which grows upwards. The heap is a singly-linked-list which is
allocated/deallocated from. The stack grows downwards to zero and
presumably starts generating errors once it underflows. An initial stack
size of 32 is chosen as that should encompass all use cases today, but
we can eventually probably add configuration for this!
Note that the heap is initialized to all
nullfor the stack and thenthe initial JS values (
undefined,null,true,false) are pushedonto the heap in reserved locations.