From a04fcce54899337602c2ea2347a8cac8c9acde1c Mon Sep 17 00:00:00 2001
From: Even Rouault <even.rouault@spatialys.com>
Date: Sat, 17 Oct 2020 17:31:19 +0200
Subject: [PATCH] Add QgsFeature::approximateMemoryUsage()

---
 python/core/auto_generated/qgsfeature.sip.in | 11 ++++
 src/core/qgsfeature.cpp                      | 54 ++++++++++++++++++++
 src/core/qgsfeature.h                        | 11 ++++
 tests/src/core/testqgsfeature.cpp            |  5 ++
 4 files changed, 81 insertions(+)

diff --git a/python/core/auto_generated/qgsfeature.sip.in b/python/core/auto_generated/qgsfeature.sip.in
index 32f0b6b9f6e..2d114f5f387 100644
--- a/python/core/auto_generated/qgsfeature.sip.in
+++ b/python/core/auto_generated/qgsfeature.sip.in
@@ -547,6 +547,17 @@ before this method can be used.
 :return: -1 if field does not exist or field map is not associated.
 
 .. seealso:: :py:func:`setFields`
+%End
+
+    int approximateMemoryUsage() const;
+%Docstring
+Returns the approximate RAM usage of the feature, in bytes.
+
+This method takes into account the size of variable elements (strings,
+geometry, ...), but the value returned should be considered as a lower
+bound estimation.
+
+.. versionadded:: 3.16
 %End
 
     operator QVariant() const;
diff --git a/src/core/qgsfeature.cpp b/src/core/qgsfeature.cpp
index b7186bf609c..de8cc0fb6b4 100644
--- a/src/core/qgsfeature.cpp
+++ b/src/core/qgsfeature.cpp
@@ -18,6 +18,8 @@ email                : sherman at mrcc.com
 #include "qgsfields.h"
 #include "qgsgeometry.h"
 #include "qgsrectangle.h"
+#include "qgsfield_p.h" // for approximateMemoryUsage()
+#include "qgsfields_p.h" // for approximateMemoryUsage()
 
 #include "qgsmessagelog.h"
 
@@ -279,6 +281,58 @@ int QgsFeature::fieldNameIndex( const QString &fieldName ) const
   return d->fields.lookupField( fieldName );
 }
 
+static size_t qgsQStringApproximateMemoryUsage( const QString &str )
+{
+  return sizeof( QString ) + str.size() * sizeof( QChar );
+}
+
+static size_t qgsQVariantApproximateMemoryUsage( const QVariant &v )
+{
+  // A QVariant has a private structure that is a union of things whose larger
+  // size if a long long, and a int
+  size_t s = sizeof( QVariant ) + sizeof( long long ) + sizeof( int );
+  if ( v.type() == QVariant::String )
+  {
+    s += qgsQStringApproximateMemoryUsage( v.toString() );
+  }
+  else if ( v.type() == QVariant::StringList )
+  {
+    for ( const QString &str : v.toStringList() )
+      s += qgsQStringApproximateMemoryUsage( str );
+  }
+  else if ( v.type() == QVariant::List )
+  {
+    for ( const QVariant &subV : v.toList() )
+      s += qgsQVariantApproximateMemoryUsage( subV );
+  }
+  return s;
+}
+
+int QgsFeature::approximateMemoryUsage() const
+{
+  size_t s = sizeof( *this ) + sizeof( *d );
+
+  // Attributes
+  for ( const QVariant &attr : qgis::as_const( d->attributes ) )
+  {
+    s += qgsQVariantApproximateMemoryUsage( attr );
+  }
+
+  // Geometry
+  s += sizeof( QAtomicInt ) + sizeof( void * ); // ~ sizeof(QgsGeometryPrivate)
+  // For simplicity we consider that the RAM usage is the one of the WKB
+  // representation
+  s += d->geometry.wkbSize();
+
+  // Fields
+  s += sizeof( QgsFieldsPrivate );
+  // TODO potentially: take into account the length of the name, comment, default value, etc...
+  s += d->fields.size() * ( sizeof( QgsField )  + sizeof( QgsFieldPrivate ) );
+
+  return static_cast<int>( s );
+}
+
+
 /***************************************************************************
  * This class is considered CRITICAL and any change MUST be accompanied with
  * full unit tests in testqgsfeature.cpp.
diff --git a/src/core/qgsfeature.h b/src/core/qgsfeature.h
index 399e56277eb..b442423054f 100644
--- a/src/core/qgsfeature.h
+++ b/src/core/qgsfeature.h
@@ -536,6 +536,17 @@ class CORE_EXPORT QgsFeature
      */
     int fieldNameIndex( const QString &fieldName ) const;
 
+    /**
+     * Returns the approximate RAM usage of the feature, in bytes.
+     *
+     * This method takes into account the size of variable elements (strings,
+     * geometry, ...), but the value returned should be considered as a lower
+     * bound estimation.
+     *
+     * \since QGIS 3.16
+     */
+    int approximateMemoryUsage() const;
+
     //! Allows direct construction of QVariants from features.
     operator QVariant() const
     {
diff --git a/tests/src/core/testqgsfeature.cpp b/tests/src/core/testqgsfeature.cpp
index 035432a65dd..961fa26c3ad 100644
--- a/tests/src/core/testqgsfeature.cpp
+++ b/tests/src/core/testqgsfeature.cpp
@@ -124,6 +124,7 @@ void TestQgsFeature::attributesTest()
 void TestQgsFeature::constructorTest()
 {
   QgsFeature f;
+  QVERIFY( f.approximateMemoryUsage() > 0 );
   QVERIFY( FID_IS_NULL( f.id() ) );
   QgsFeature f2 { QgsFields() };
   QVERIFY( FID_IS_NULL( f2.id() ) );
@@ -222,6 +223,7 @@ void TestQgsFeature::attributes()
   feature.setAttributes( mAttrs );
   QCOMPARE( feature.attributes(), mAttrs );
   QCOMPARE( feature.attributes(), mAttrs );
+  QVERIFY( feature.approximateMemoryUsage() > QgsFeature().approximateMemoryUsage() );
 
   //test implicit sharing detachment
   QgsFeature copy( feature );
@@ -286,6 +288,7 @@ void TestQgsFeature::geometry()
   //test no double delete of geometry when setting:
   feature.setGeometry( QgsGeometry( mGeometry2 ) );
   QVERIFY( feature.hasGeometry() );
+  QVERIFY( feature.approximateMemoryUsage() > QgsFeature().approximateMemoryUsage() );
   feature.setGeometry( QgsGeometry( mGeometry ) );
   QCOMPARE( feature.geometry().asWkb(), mGeometry.asWkb() );
 
@@ -355,6 +358,8 @@ void TestQgsFeature::fields()
   QVERIFY( original.fields().isEmpty() );
   original.setFields( mFields );
   QCOMPARE( original.fields(), mFields );
+  QVERIFY( original.approximateMemoryUsage() > QgsFeature().approximateMemoryUsage() );
+
   QgsFeature copy( original );
   QCOMPARE( copy.fields(), original.fields() );