SocketClient: add optional reference counting

Needed to fix a race in netd.

Bug: 3438459
Change-Id: Icd7f5f035510235f733a25c0621479d3e644b152
diff --git a/include/sysutils/SocketClient.h b/include/sysutils/SocketClient.h
index 2fcc331..ef6dd9b 100644
--- a/include/sysutils/SocketClient.h
+++ b/include/sysutils/SocketClient.h
@@ -19,6 +19,10 @@
     /* Peer group ID */
     gid_t mGid;
 
+    /* Reference count (starts at 1) */
+    pthread_mutex_t mRefCountMutex;
+    int mRefCount;
+
 public:
     SocketClient(int sock);
     virtual ~SocketClient() {}
@@ -34,6 +38,13 @@
 
     // Sending binary data:
     int sendData(const void *data, int len);
+
+    // Optional reference counting.  Reference count starts at 1.  If
+    // it's decremented to 0, it deletes itself.
+    // SocketListener creates a SocketClient (at refcount 1) and calls
+    // decRef() when it's done with the client.
+    void incRef();
+    void decRef();
 };
 
 typedef android::List<SocketClient *> SocketClientCollection;