Thrift: A hack to prevent incorrect usage of Mutex Guards.

Reviewed By: boz

Test Plan:
dreiss@dreiss-vmware:safe_concurrency:thrift/test$ nl -ba guard_test.cc
     1  #include "../lib/cpp/src/concurrency/Mutex.h"
     2  using facebook::thrift::concurrency::Guard;
     3  void test() {
     4    facebook::thrift::concurrency::Mutex m;
     5    Guard(m);
     6    Guard g1(m);
     7
     8    facebook::thrift::concurrency::ReadWriteMutex rwm;
     9    facebook::thrift::concurrency::RWGuard(m);
    10    facebook::thrift::concurrency::RWGuard g2(rwm);
    11  }
dreiss@dreiss-vmware:safe_concurrency:thrift/test$ g++ -c guard_test.cc
guard_test.cc: In function ‘void test()’:
guard_test.cc:5: error: ‘incorrect_use_of_Guard’ was not declared in this scope
guard_test.cc:9: error: ‘incorrect_use_of_RWGuard’ is not a member of ‘facebook::thrift::concurrency’
dreiss@dreiss-vmware:safe_concurrency:thrift/test$

Revert Plan: ok


git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@665402 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/lib/cpp/src/concurrency/Mutex.h b/lib/cpp/src/concurrency/Mutex.h
index 7594339..f3c7cd0 100644
--- a/lib/cpp/src/concurrency/Mutex.h
+++ b/lib/cpp/src/concurrency/Mutex.h
@@ -83,6 +83,12 @@
 };  
 
 
+// A little hack to prevent someone from trying to do "Guard(m);"
+// Sorry for polluting the global namespace, but I think it's worth it.
+#define Guard(m) incorrect_use_of_Guard(m)
+#define RWGuard(m) incorrect_use_of_RWGuard(m)
+
+
 }}} // facebook::thrift::concurrency
 
 #endif // #ifndef _THRIFT_CONCURRENCY_MUTEX_H_