HTTPASYNC-56: Removed method level synchronization in MinimalClientExchangeHandlerImpl and DefaultClientExchangeHandlerImpl. Instances of both classes are expected to be accessed by one thread at a time. Only #cancel method can be used safely by multiple threads concurrently.
httpcomponents/httpasyncclient/trunk/httpasyncclient/src/main/java/org/apache/http/impl/nio/client/DefaultClientExchangeHandlerImpl.java