Avoid COW overhead using css::uno::Sequence

The scenarios are:

1. Calling sequence's begin() and end() in pairs to pass to algorithms
(both calls use getArray(), which does the COW checks)
2. In addition to #1, calling end() again when checking result of find
algorithms, and/or begin() to calculate result's distance
3. Using non-const sequences in range-based for loops, which internally
do #1
4. Assigning sequence to another sequence variable, and then modifying
one of them

In many cases, the sequences could be made const, or treated as const
for the purposes of the algorithms (using std::as_const, std::cbegin,
and std::cend). Where algorithm modifies the sequence, it was changed
to only call getArray() once. For that, css::uno::toNonConstRange was
introduced, which returns a struct (sublclass of std::pair) with two
iterators [begin, end], that are calculated using one call to begin()
and one call to getLength().

To handle #4, css::uno::Sequence::swap was introduced, that swaps the
internal pointer to uno_Sequence. So when a local Sequence variable
should be assigned to another variable, and the latter will be modified
further, it's now possible to use swap instead, so the two sequences
are kept independent.

The modified places were found by temporarily removing non-const end().

Change-Id: I8fe2787f200eecb70744e8b77fbdf7a49653f628
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/123542
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

5 files changed, 14 insertions, 10 deletions

diff --git a/connectivity/source/commontools/ConnectionWrapper.cxx b/connectivity/source/commontools/ConnectionWrapper.cxx
index 264002e5dc57..252882067865 100644
--- a/connectivity/source/commontools/ConnectionWrapper.cxx
+++ b/connectivity/source/commontools/ConnectionWrapper.cxx
@@ -199,7 +199,8 @@ void OConnectionWrapper::createUniqueId( const OUString& _rURL
     if ( !_rPassword.isEmpty() )
         sha1.update(reinterpret_cast<unsigned char const*>(_rPassword.getStr()), _rPassword.getLength() * sizeof(sal_Unicode));
     // now we need to sort the properties
-    std::sort(_rInfo.begin(),_rInfo.end(),TPropertyValueLessFunctor());
+    auto [begin, end] = toNonConstRange(_rInfo);
+    std::sort(begin,end,TPropertyValueLessFunctor());
 
     for (PropertyValue const & prop : std::as_const(_rInfo))
     {
diff --git a/connectivity/source/commontools/dbtools2.cxx b/connectivity/source/commontools/dbtools2.cxx
index c0cefeaa1b13..0adfe23bdac9 100644
--- a/connectivity/source/commontools/dbtools2.cxx
+++ b/connectivity/source/commontools/dbtools2.cxx
@@ -637,11 +637,11 @@ bool isDataSourcePropertyEnabled(const Reference<XInterface>& _xProp, const OUSt
         {
             Sequence< PropertyValue > aInfo;
             xProp->getPropertyValue("Info") >>= aInfo;
-            const PropertyValue* pValue =std::find_if(aInfo.begin(),
-                                                aInfo.end(),
+            const PropertyValue* pValue =std::find_if(std::cbegin(aInfo),
+                                                std::cend(aInfo),
                                                 [&_sProperty](const PropertyValue& lhs)
                                                 { return lhs.Name == _sProperty; });
-            if ( pValue != aInfo.end() )
+            if ( pValue != std::cend(aInfo) )
                 pValue->Value >>= bEnabled;
         }
     }
diff --git a/connectivity/source/drivers/jdbc/JStatement.cxx b/connectivity/source/drivers/jdbc/JStatement.cxx
index 40fef64ed5ac..da06ef77f2c3 100644
--- a/connectivity/source/drivers/jdbc/JStatement.cxx
+++ b/connectivity/source/drivers/jdbc/JStatement.cxx
@@ -124,9 +124,10 @@ Sequence< Type > SAL_CALL java_sql_Statement_Base::getTypes(  )
     Sequence< Type > aOldTypes = java_sql_Statement_BASE::getTypes();
     if ( m_pConnection.is() && !m_pConnection->isAutoRetrievingEnabled() )
     {
-        auto newEnd = std::remove(aOldTypes.begin(), aOldTypes.end(),
+        auto [begin, end] = toNonConstRange(aOldTypes);
+        auto newEnd = std::remove(begin, end,
                                   cppu::UnoType<XGeneratedResultSet>::get());
-        aOldTypes.realloc(std::distance(aOldTypes.begin(), newEnd));
+        aOldTypes.realloc(std::distance(begin, newEnd));
     }
 
     return ::comphelper::concatSequences(aTypes.getTypes(),aOldTypes);
diff --git a/connectivity/source/drivers/odbc/OStatement.cxx b/connectivity/source/drivers/odbc/OStatement.cxx
index c5d63ef771a8..13ffeda8e4ba 100644
--- a/connectivity/source/drivers/odbc/OStatement.cxx
+++ b/connectivity/source/drivers/odbc/OStatement.cxx
@@ -131,9 +131,10 @@ Sequence< Type > SAL_CALL OStatement_Base::getTypes(  )
     Sequence< Type > aOldTypes = OStatement_BASE::getTypes();
     if ( m_pConnection.is() && !m_pConnection->isAutoRetrievingEnabled() )
     {
-        auto newEnd = std::remove(aOldTypes.begin(), aOldTypes.end(),
+        auto [begin, end] = toNonConstRange(aOldTypes);
+        auto newEnd = std::remove(begin, end,
                                   cppu::UnoType<XGeneratedResultSet>::get());
-        aOldTypes.realloc(std::distance(aOldTypes.begin(), newEnd));
+        aOldTypes.realloc(std::distance(begin, newEnd));
     }
 
     return ::comphelper::concatSequences(aTypes.getTypes(),aOldTypes);
diff --git a/connectivity/source/sdbcx/VDescriptor.cxx b/connectivity/source/sdbcx/VDescriptor.cxx
index 9023a2076a74..2392e2d5f1d2 100644
--- a/connectivity/source/sdbcx/VDescriptor.cxx
+++ b/connectivity/source/sdbcx/VDescriptor.cxx
@@ -74,10 +74,11 @@ namespace connectivity::sdbcx
             Sequence< Property > aProperties;
             describeProperties( aProperties );
 
+            auto [begin, end] = toNonConstRange(aProperties);
             if ( isNew() )
-                std::for_each( aProperties.begin(), aProperties.end(), ResetROAttribute() );
+                std::for_each( begin, end, ResetROAttribute() );
             else
-                std::for_each( aProperties.begin(), aProperties.end(), SetROAttribute() );
+                std::for_each( begin, end, SetROAttribute() );
 
             return new ::cppu::OPropertyArrayHelper( aProperties );
         }