Add base::mac::ScopedMachPortSet.

Contrary to its documentation, kqueue()'s EVFILT_MACHPORT doesn't work
with raw Mach receive rights, it only works with port sets. It's easy
enough to add a receive right to a port set, but we should have a scoper
to dispose of the port set.

R=rsesek@chromium.org

Review URL: https://codereview.chromium.org/749693002

Cr-Commit-Position: refs/heads/master@{#305228}

2 files changed, 29 insertions, 0 deletions

diff --git a/base/mac/scoped_mach_port.cc b/base/mac/scoped_mach_port.cc
index de94602..13307f2 100644
--- a/base/mac/scoped_mach_port.cc
+++ b/base/mac/scoped_mach_port.cc
@@ -25,6 +25,14 @@ void ReceiveRightTraits::Free(mach_port_t port) {
       << "ScopedMachReceiveRight mach_port_mod_refs";
 }
 
+// static
+void PortSetTraits::Free(mach_port_t port) {
+  kern_return_t kr =
+      mach_port_mod_refs(mach_task_self(), port, MACH_PORT_RIGHT_PORT_SET, -1);
+  MACH_LOG_IF(ERROR, kr != KERN_SUCCESS, kr)
+      << "ScopedMachPortSet mach_port_mod_refs";
+}
+
 }  // namespace internal
 }  // namespace mac
 }  // namespace base
diff --git a/base/mac/scoped_mach_port.h b/base/mac/scoped_mach_port.h
index 36087c9..9ef90d6 100644
--- a/base/mac/scoped_mach_port.h
+++ b/base/mac/scoped_mach_port.h
@@ -31,6 +31,14 @@ struct BASE_EXPORT ReceiveRightTraits {
   static void Free(mach_port_t port);
 };
 
+struct PortSetTraits {
+  static mach_port_t InvalidValue() {
+    return MACH_PORT_NULL;
+  }
+
+  static void Free(mach_port_t port);
+};
+
 }  // namespace internal
 
 // A scoper for handling a Mach port that names a send right. Send rights are
@@ -59,6 +67,19 @@ class BASE_EXPORT ScopedMachReceiveRight :
   operator mach_port_t() const { return get(); }
 };
 
+// A scoper for handling a Mach port set. A port set can have only one
+// reference. This takes ownership of that single reference on construction and
+// destroys the port set on destruction. Destroying a port set does not destroy
+// the receive rights that are members of the port set.
+class BASE_EXPORT ScopedMachPortSet :
+    public ScopedGeneric<mach_port_t, internal::PortSetTraits> {
+ public:
+  explicit ScopedMachPortSet(mach_port_t port = traits_type::InvalidValue())
+      : ScopedGeneric(port) {}
+
+  operator mach_port_t() const { return get(); }
+};
+
 }  // namespace mac
 }  // namespace base