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Implement a TODO: cache the list of MS TZ IDs

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The MS TZ-backend's lookup of available Windows IDs included a TODO
advocating caching the result, since it is unlikely to change at
runtime. Given that MS's time_t functions don't believe in times
before 1970 and two-digit year parsing (such as the ASN.1 parser does,
apparently many times, during SSL handshakes) assumes the 1900s (and
certs in use today have mostly been issued this century), SSL involves
DTP falling back repeatedly to lookups of local time's offsets from
UTC (before it discovers it shouldn't have been using local time
anyway) via the system timezone object, this cacheable list can be
accessed many times. (A user has reported thousands per SSL socket
created.) So let's implement that TODO and trust that updates to the
registry's set of available zones aren't a common occurrence at
runtime.

Pick-to: 6.5
Change-Id: Iefe235c71da1bf5c3372c52dba89ad0657e06c0b
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit d59e539b3a1252aa22783c4fdf1e22b35e5a4292)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Edward Welbourne 2023-11-14 11:14:38 +01:00 committed by Qt Cherry-pick Bot
parent 170d903a7e
commit 14f5eaaf58
1 changed files with 16 additions and 14 deletions
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4
src/corelib/time/qtimezoneprivate_win.cpp
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@ -186,7 +186,7 @@ bool isSameRule(const QWinTimeZonePrivate::QWinTransitionRule &last,
QList<QByteArray> availableWindowsIds()
{
// TODO Consider caching results in a global static, very unlikely to change.
static const QList<QByteArray> cache = [] {
QList<QByteArray> list;
QWinRegistryKey key(HKEY_LOCAL_MACHINE, tzRegPath);
if (key.isValid()) {
@ -202,6 +202,8 @@ QList<QByteArray> availableWindowsIds()
}
}
return list;
}();
return cache;
}
QByteArray windowsSystemZoneId()