mojo: Don't leak handles when assigning to ScopedHandles.

mojo/public/cpp/system/core.h

Index: mojo/public/cpp/system/core.h
diff --git a/mojo/public/cpp/system/core.h b/mojo/public/cpp/system/core.h
index 2b1caa914a4b69770a9e632dbad6e01564bb5229..b7d0456bdc04ca7f23958351f54199003b7aac59 100644
--- a/mojo/public/cpp/system/core.h
+++ b/mojo/public/cpp/system/core.h
@@ -107,6 +107,8 @@ class ScopedHandleBase {
   // Move-only constructor and operator=.
   ScopedHandleBase(RValue other) : handle_(other.object->release()) {}
   ScopedHandleBase& operator=(RValue other) {
+    if (handle_.is_valid() && handle_.value() != other.object->get().value())

[viettrungluu, 2014/06/17 22:58:25]

Since a handle should only be in a single ScopedHandleBase<> at any particular
time, you could simplify this to:

if (other.object != this)
  CloseIfNecessary();

(CloseIfNecessary() checks for validity).

Or maybe better (more self-evidently correct):

if (other.object != this) {
  CloseIfNecessary();
  handle_ = other.object->release();
}
return *this;

You might also add an |assert(handle_.value() != other.object->get().value());|
before the |CloseIfNecessary();| (inside the if block).

[Elliot Glaysher, 2014/06/17 23:08:28]

Switched to if (other.object != this). Didn't add the assert, because wouldn't
that trigger on an assignment of a closed handle to a closed handle?

+      CloseIfNecessary();
     handle_ = other.object->release();
     return *this;
   }