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Fixing a memory leak #1099

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Fixing a memory leak #1099

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Jaders77
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@Jaders77 Jaders77 commented May 23, 2018

This part of the code makes a copy of the original reference without calling the destructor at any time for it (original reference).
Instead of using a default constructor / copy constructor and then one destructor for each, such C++ copy elision optimization, it's better to simply remove copy.

Simple example of the problem:

public global::Lldb.SBSymbolContext GetSymbolContext(uint resolve_scope)
{
  var __ret = new global::Lldb.SBSymbolContext.__Internal();
  __Internal.GetSymbolContext((__Instance + __PointerAdjustment), new IntPtr(&__ret), resolve_scope); // here __ret is initialized like a constructor
  return global::Lldb.SBSymbolContext.__CreateInstance(__ret);
}

internal static global::Lldb.SBSymbolContext __CreateInstance(global::Lldb.SBSymbolContext.__Internal native, bool skipVTables = false)
{
  return new global::Lldb.SBSymbolContext(native, skipVTables);
}

private SBSymbolContext(global::Lldb.SBSymbolContext.__Internal native, bool skipVTables = false)
  : this(__CopyValue(native), skipVTables)
{
  __ownsNativeInstance = true;
  NativeToManagedMap[__Instance] = this;
}

private static void* __CopyValue(global::Lldb.SBSymbolContext.__Internal native)
{
  var ret = Marshal.AllocHGlobal(sizeof(global::Lldb.SBSymbolContext.__Internal));
  global::Lldb.SBSymbolContext.__Internal.cctor(ret, new global::System.IntPtr(&native));
  return ret.ToPointer();
}

After the fix:

private static void* __CopyValue(global::Lldb.SBSymbolContext.__Internal native)
{
  var ret = Marshal.AllocHGlobal(sizeof(global::Lldb.SBSymbolContext.__Internal));
  *(global::Lldb.SBSymbolContext.__Internal*) ret = native;
  return ret.ToPointer();
}

This part of the code makes a copy of the original reference without calling the destructor at any time for it (original reference).
Instead of using a default constructor / copy constructor and then one destructor for each, such C++ copy elision optimization, it's better to simply remove copy.

Simple example of the problem:
public global::Lldb.SBSymbolContext GetSymbolContext(uint resolve_scope)
{
  var __ret = new global::Lldb.SBSymbolContext.__Internal();
  __Internal.GetSymbolContext((__Instance + __PointerAdjustment), new IntPtr(&__ret), resolve_scope); // here __ret is initialized like a constructor
  return global::Lldb.SBSymbolContext.__CreateInstance(__ret);
}

internal static global::Lldb.SBSymbolContext __CreateInstance(global::Lldb.SBSymbolContext.__Internal native, bool skipVTables = false)
{
  return new global::Lldb.SBSymbolContext(native, skipVTables);
}

private SBSymbolContext(global::Lldb.SBSymbolContext.__Internal native, bool skipVTables = false)
  : this(__CopyValue(native), skipVTables)
{
  __ownsNativeInstance = true;
  NativeToManagedMap[__Instance] = this;
}

private static void* __CopyValue(global::Lldb.SBSymbolContext.__Internal native)
{
  var ret = Marshal.AllocHGlobal(sizeof(global::Lldb.SBSymbolContext.__Internal));
  global::Lldb.SBSymbolContext.__Internal.cctor(ret, new global::System.IntPtr(&native));
  return ret.ToPointer();
}

After the fix:
private static void* __CopyValue(global::Lldb.SBSymbolContext.__Internal native)
{
  var ret = Marshal.AllocHGlobal(sizeof(global::Lldb.SBSymbolContext.__Internal));
  *(global::Lldb.SBSymbolContext.__Internal*) ret = native;
  return ret.ToPointer();
}
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dnfclas commented May 23, 2018

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@tritao tritao requested a review from ddobrev May 24, 2018 14:51
@ddobrev ddobrev force-pushed the master branch 12 times, most recently from 0464938 to 637018f Compare October 15, 2018 05:15
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The generated code now does not call the non-trivial constructor if any. I think this might lead to incorrect behaviours on the native side.

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3 participants