42 lines
1.9 KiB
Plaintext
42 lines
1.9 KiB
Plaintext
DBMON notes
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10/7/94
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The first DWORD of the shared memory buffer contains the process ID of the
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client that sent the debug string. DBMON will print the process ID if the
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previous line printed was from another process, or if the previous line was
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from the same process and ended in a newline.
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The shared memory buffer must be 4096 bytes. If it is larger, it won't do any
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good. If it is smaller, nothing terrible will happen, but strings larger than
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the buffer will not be delivered, and a complaining message will be sent to the
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kernel debugger by the client. Why is it this size? Because shared memory
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comes in page-sized chunks, so we might as well ask for as much as will be used
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on the machines with the smallest pages. On machines with larger pages, the
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remainder of the page will be wasted anyway.
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Event DBWIN_BUFFER_READY must be an auto-reset event, so that only one client
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thread will use the buffer at a time. Using a manual reset event with
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PulseEvent will not work.
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Event DBWIN_DATA_READY need not be auto-reset, but it is simpler that way.
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Allowing multiple copies of DBMON to run might be amusing, put not particularly
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useful. As I originally wrote it, the messages were distributed randomly among
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the DBMON instances or be garbled. I added a check for ERROR_ALREADY_EXISTS so
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it won't run twice. The worst you can do to the client is cause it to print a
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message on the kernel debugger, as above.
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If DBMON is broken and never calls SetEvent(AckEvent), it will cause a 10
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second delay in the client every time OutputDebugString is called, then the
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message will be printed on the kernel debugger.
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OutputDebugString will force synchronization of client threads when DBMON is
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running. Letting the kernel debugger catch the strings will also synchronize
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threads, but the timing effects may be different. Caveat emptor.
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In a GUI version of DBMON, use MsgWaitForMultipleObjects.
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