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Copy memory to buffer when saving files on wasm with threading on

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wasm heap uses a shared array buffer, which cannot be fed to
FileSystemWritableFileStream.write due to security limitations.
Heap memory has to be copied to a temporary buffer for the operation to
succeed.
This is only done if __EMSCRIPTEN_SHARED_MEMORY__ is on to optimize the
non-threading path.

Fixes: QTBUG-112881
Pick-to: 6.5
Change-Id: I0d117a8703caf4c17abc67b30df5248a53406d5f
Reviewed-by: Aleksandr Reviakin <aleksandr.reviakin@qt.io>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>
This commit is contained in:
Mikolaj Boc 2023-04-21 13:42:57 +02:00
parent 5ebb9a8bf3
commit d09855ae7b
1 changed files with 28 additions and 4 deletions
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32
src/gui/platform/wasm/qwasmlocalfileaccess.cpp
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@ -258,6 +258,11 @@ void saveDataToFileInChunks(emscripten::val fileHandle, const QByteArray &data)
std::function<void(val result)> continuation;
};
static constexpr size_t desiredChunkSize = 1024u;
#if defined(__EMSCRIPTEN_SHARED_MEMORY__)
qstdweb::Uint8Array chunkArray(desiredChunkSize);
#endif
auto state = std::make_shared<State>();
state->written = 0u;
state->continuation = [=](val) mutable {
@ -267,11 +272,30 @@ void saveDataToFileInChunks(emscripten::val fileHandle, const QByteArray &data)
state.reset();
return;
}
static constexpr size_t desiredChunkSize = 1024u;
const auto currentChunkSize = std::min(remaining, desiredChunkSize);
Promise::make(writable, QStringLiteral("write"), {
.thenFunc = state->continuation,
}, val(typed_memory_view(currentChunkSize, data.constData() + state->written)));
#if defined(__EMSCRIPTEN_SHARED_MEMORY__)
// If shared memory is used, WebAssembly.Memory is instantiated with the 'shared'
// option on. Passing a typed_memory_view to SharedArrayBuffer to
// FileSystemWritableFileStream.write is disallowed by security policies, so we
// need to make a copy of the data to a chunk array buffer.
Promise::make(
writable, QStringLiteral("write"),
{
.thenFunc = state->continuation,
},
chunkArray.copyFrom(data.constData() + state->written, currentChunkSize)
.val()
.call<emscripten::val>("subarray", emscripten::val(0),
emscripten::val(currentChunkSize)));
#else
Promise::make(writable, QStringLiteral("write"),
{
.thenFunc = state->continuation,
},
val(typed_memory_view(currentChunkSize, data.constData() + state->written)));
#endif
state->written += currentChunkSize;
};