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fix(shell): retry clipboard reads briefly before failing (#38) #191

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Merged
JavaZeroo merged 1 commit into from
Oct 29, 2026
Merged

fix(shell): retry clipboard reads briefly before failing (#38) #191

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18 changes: 15 additions & 3 deletions experiments/shell/clipboard.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13,16 +13,28 @@ class ClipboardError : public std::runtime_error {
};
class ClipboardAccess {
public:
explicit ClipboardAccess(HWND owner) {
if (!OpenClipboard(owner)) throw ClipboardError("OpenClipboard", GetLastError());
// A hosted desktop can hold the clipboard for a few milliseconds at a time
// (Explorer or a neighbouring test). Reads retry briefly so contention is
// not reported as a hard refusal; writes keep the immediate failure because
// the copy-failure contract asserts the first OpenClipboard result.
explicit ClipboardAccess(HWND owner, bool retry = false) {
constexpr int attempts = 5;
for (int attempt = 0; attempt < attempts; ++attempt) {
if (OpenClipboard(owner)) return;
const DWORD error = GetLastError();
if (!retry || error != ERROR_ACCESS_DENIED || attempt + 1 == attempts)
throw ClipboardError("OpenClipboard", error);
Sleep(static_cast<DWORD>(20 * (attempt + 1)));
}
throw ClipboardError("OpenClipboard", GetLastError());
}
~ClipboardAccess() { CloseClipboard(); }
ClipboardAccess(const ClipboardAccess&) = delete;
};
inline std::u16string read_unicode_clipboard(HWND owner, size_t max_units = PastePolicy::hard_utf16_units) {
static_assert(sizeof(wchar_t) == sizeof(char16_t), "Windows UTF-16 expected");
if (max_units > PastePolicy::hard_utf16_units) throw std::length_error("clipboard limit exceeds hard bound");
ClipboardAccess clipboard(owner);
ClipboardAccess clipboard(owner, true);
if (!IsClipboardFormatAvailable(CF_UNICODETEXT)) throw ClipboardError("Unicode text unavailable", ERROR_NOT_FOUND);
HANDLE memory = GetClipboardData(CF_UNICODETEXT);
if (!memory) throw ClipboardError("GetClipboardData", GetLastError());
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