@samitouri / QOSAMI-WSL-1 / commits / c85e6ab4

Improve registry enumeration performance (#40828)

* Improve registry enumeration performance - Extend QueryInfo to expose subkey and value counts from RegQueryInfoKeyW, enabling callers to pre-allocate collections. - Add reserve() calls in EnumGuidKeys and EnumValues to eliminate vector reallocations during registry enumeration. These functions are on the critical path for distro listing and plugin loading. - Replace emplace_back(std::make_pair(...)) with direct emplace_back in EnumGuidKeys to avoid unnecessary pair construction overhead. - Eliminate temporary std::wstring allocations in ReportErrorIfFailed by appending a char literal and the LPCWSTR directly instead of constructing intermediate wstring objects for concatenation. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Use _Out_opt_ for QueryInfo subkey/value count out-params Address PR review feedback: the new SubKeyCount/ValueCount parameters are output values filled by RegQueryInfoKeyW, so annotate them with _Out_opt_ rather than _In_opt_ for correct SAL/static analysis. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> --------- Co-authored-by: Ben Hillis <benhill@ntdev.microsoft.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Ben Hillis committed Jun 17, 2026 at 20:11 UTC c85e6ab40a35760f75adca587bc5a0ada7d9efe8

2 files changed +26 -7

src/windows/common/registry.cpp

+19 -6

@@ -76,12 +76,14 @@ void ReportErrorIfFailed(_In_ LSTATUS Error, _In_ HKEY Key, _In_opt_ LPCWSTR Sub

76 auto path = GetKeyPath(Key);

77 if (Subkey != nullptr)

78 {

79 - path += L"\\" + std::wstring(Subkey);

79 + path += L'\\';

80 + path += Subkey;

81 }

83 if (Value != nullptr)

84 {

84 - path += L"\\" + std::wstring(Value);

85 + path += L'\\';

86 + path += Value;

87 }

89 if (wsl::windows::common::ExecutionContext::ShouldCollectErrorMessage())

@@ -174,6 +176,9 @@ std::vector<std::pair<GUID, std::wstring>> wsl::windows::common::registry::EnumG

176 // Iterate through the provided keys and return a list of all sub-keys that are GUIDs.

177 WCHAR buffer[39];

178 std::vector<std::pair<GUID, std::wstring>> subKeys;

179 + DWORD subKeyCount = 0;

180 + QueryInfo(Key, nullptr, nullptr, nullptr, &subKeyCount);

181 + subKeys.reserve(subKeyCount);

182 DWORD index = 0;

183 for (;;)

184 {

@@ -198,7 +203,7 @@ std::vector<std::pair<GUID, std::wstring>> wsl::windows::common::registry::EnumG

203 continue;

204 }

205

201 - subKeys.emplace_back(std::make_pair(guid.value(), std::wstring(buffer)));

206 + subKeys.emplace_back(guid.value(), std::wstring(buffer));

207 }

208

209 return subKeys;

@@ -208,7 +213,9 @@ std::vector<std::pair<std::wstring, DWORD>> wsl::windows::common::registry::Enum

213 {

214 std::vector<std::pair<std::wstring, DWORD>> values;

215 DWORD maxValueNameSize = 0;

211 - QueryInfo(Key, nullptr, &maxValueNameSize);

216 + DWORD valueCount = 0;

217 + QueryInfo(Key, nullptr, &maxValueNameSize, nullptr, nullptr, &valueCount);

218 + values.reserve(valueCount);

219

220 for (DWORD Index = 0;; Index++)

221 {

@@ -314,10 +321,16 @@ wil::unique_hkey wsl::windows::common::registry::OpenOrCreateLxssDiskMountsKey(_

321 return CreateKey(HKEY_LOCAL_MACHINE, path.c_str(), KEY_ALL_ACCESS, nullptr, REG_OPTION_VOLATILE);

322 }

323

317 -void wsl::windows::common::registry::QueryInfo(_In_ HKEY Key, _In_opt_ DWORD* MaxSubKeySize, _In_opt_ DWORD* MaxValueNameSize, _In_opt_ DWORD* MaxValueDataSize)

324 +void wsl::windows::common::registry::QueryInfo(

325 + _In_ HKEY Key,

326 + _In_opt_ DWORD* MaxSubKeySize,

327 + _In_opt_ DWORD* MaxValueNameSize,

328 + _In_opt_ DWORD* MaxValueDataSize,

329 + _Out_opt_ DWORD* SubKeyCount,

330 + _Out_opt_ DWORD* ValueCount)

331 {

332 const auto error = (RegQueryInfoKeyW(

320 - Key, nullptr, nullptr, nullptr, nullptr, MaxSubKeySize, nullptr, nullptr, MaxValueNameSize, MaxValueDataSize, nullptr, nullptr));

333 + Key, nullptr, nullptr, nullptr, SubKeyCount, MaxSubKeySize, nullptr, ValueCount, MaxValueNameSize, MaxValueDataSize, nullptr, nullptr));

334

335 ReportErrorIfFailed(error, Key, nullptr, nullptr);

336 }

src/windows/common/registry.hpp

+7 -1

@@ -53,7 +53,13 @@ wil::unique_hkey OpenLxssUserKey();

54 wil::unique_hkey OpenOrCreateLxssDiskMountsKey(_In_ PSID UserSid);

56 -void QueryInfo(_In_ HKEY Key, _In_opt_ DWORD* MaxSubKeySize = nullptr, _In_opt_ DWORD* MaxValueNameSize = nullptr, _In_opt_ DWORD* MaxValueDataSize = nullptr);

56 +void QueryInfo(

57 + _In_ HKEY Key,

58 + _In_opt_ DWORD* MaxSubKeySize = nullptr,

59 + _In_opt_ DWORD* MaxValueNameSize = nullptr,

60 + _In_opt_ DWORD* MaxValueDataSize = nullptr,

61 + _Out_opt_ DWORD* SubKeyCount = nullptr,

62 + _Out_opt_ DWORD* ValueCount = nullptr);

64 DWORD

65 ReadDword(_In_ HKEY Key, _In_opt_ LPCWSTR KeyName, _In_opt_ LPCWSTR ValueName, _In_ DWORD DefaultValue);