With the help of my mentor and Richard Braun, My code demo  HDebugger  can continue from a breakpointer.

After add a thread_abort()  the inferior can resume from breakpoint. Thread_abort() is to clean up the waiting event on specific thread. In the practice I have also got clear about the asynchronous RPC.

The HDebugger now can insert breakpoint, access inferior's memory and modify registers thus haven't implemented the interactive interface yet. For the incoming mid-evaluate, I don't plan to continue the HDebugger, I will begin to code gdbserver.

BTW, I haven't understand the msg_sig_post() call, how is the signal delivered? As gdb is listening on the inferior's exception port, then gdb post a signal to that port. That says: gdb post a message to herself, and handle it. Seems no use, but the msg_sig_post() is essential when gdb resume a inferior. So there must be wrong in my understand.