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ICU-21591 Release lock in SimpleDateFormat::tzFormat in case of failure

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Also remove the use of the unsafe double-checked lock idiom in the same
function, SimpleDateFormat::tzFormat(). Synchronization now always uses a
mutex, which is slower, but in the context of format or parse operations,
shouldn't be significant.

Added synchronization to one more unsafe direct reference to a const
SimpleDateFormat::fTimeZoneFormat. In the assignment operator.
This commit is contained in:
Andy Heninger 2021-04-25 15:45:18 -07:00
parent f3f24f1423
commit 7577899ff3
1 changed files with 27 additions and 17 deletions
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44
icu4c/source/i18n/smpdtfmt.cpp
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@ -64,6 +64,7 @@
#include "uassert.h"
#include "cmemory.h"
#include "umutex.h"
#include "mutex.h"
#include <float.h>
#include "smpdtfst.h"
#include "sharednumberformat.h"
@ -594,11 +595,29 @@ SimpleDateFormat& SimpleDateFormat::operator=(const SimpleDateFormat& other)
fLocale = other.fLocale;
// TimeZoneFormat can now be set independently via setter.
// If it is NULL, it will be lazily initialized from locale
// If it is NULL, it will be lazily initialized from locale.
delete fTimeZoneFormat;
fTimeZoneFormat = NULL;
if (other.fTimeZoneFormat) {
fTimeZoneFormat = new TimeZoneFormat(*other.fTimeZoneFormat);
fTimeZoneFormat = nullptr;
TimeZoneFormat *otherTZFormat;
{
// Synchronization is required here, when accessing other.fTimeZoneFormat,
// because another thread may be concurrently executing other.tzFormat(),
// a logically const function that lazily creates other.fTimeZoneFormat.
//
// Without synchronization, reordered memory writes could allow us
// to see a non-null fTimeZoneFormat before the object itself was
// fully initialized. In case of a race, it doesn't matter whether
// we see a null or a fully initialized other.fTimeZoneFormat,
// only that we avoid seeing a partially initialized object.
//
// Once initialized, no const function can modify fTimeZoneFormat,
// meaning that once we have safely grabbed the other.fTimeZoneFormat
// pointer, continued synchronization is not required to use it.
Mutex m(&LOCK);
otherTZFormat = other.fTimeZoneFormat;
}
if (otherTZFormat) {
fTimeZoneFormat = new TimeZoneFormat(*otherTZFormat);
}
#if !UCONFIG_NO_BREAK_ITERATION
@ -4308,19 +4327,10 @@ SimpleDateFormat::skipUWhiteSpace(const UnicodeString& text, int32_t pos) const
// Lazy TimeZoneFormat instantiation, semantically const.
TimeZoneFormat *
SimpleDateFormat::tzFormat(UErrorCode &status) const {
if (fTimeZoneFormat == NULL) {
umtx_lock(&LOCK);
{
if (fTimeZoneFormat == NULL) {
TimeZoneFormat *tzfmt = TimeZoneFormat::createInstance(fLocale, status);
if (U_FAILURE(status)) {
return NULL;
}
const_cast<SimpleDateFormat *>(this)->fTimeZoneFormat = tzfmt;
}
}
umtx_unlock(&LOCK);
Mutex m(&LOCK);
if (fTimeZoneFormat == nullptr && U_SUCCESS(status)) {
const_cast<SimpleDateFormat *>(this)->fTimeZoneFormat =
TimeZoneFormat::createInstance(fLocale, status);
}
return fTimeZoneFormat;
}