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Post subject: Msg passing approaches under Qnet
 Posted: Mar 01, 2008 - 12:45 PM
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Active Member
Joined: Oct 15, 2007
Posts: 58
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I have developed an adhoc network among several 6.3.2 machines. Currently, one need to communicate with one another.
e.g, one process on machine A has generated some data from the data acquisition board and do some processing with it,
then the processed data need to be transferred to another process in machine B.
As i know, one way is that A put the processed data in a file, then B can access the data across the Qnet, much like
write and open a file on the wireless network. But it seems to me not very efficient, any other better ways of
transferring data? Thank u. |
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Post subject: RE: Msg passing approaches under Qnet
Posted: Mar 01, 2008 - 04:38 PM
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QNX Master
Joined: Jun 25, 2003
Posts: 974
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This can be done with message passing in two ways.
1) machine A sends a message to machine B with the data. machine B replies when it gets it.
2) machine B sends a message to machine A saying it is ready to receive data. When machine A has data, it returns it to B in a Reply.
It may be the case that you want to use 1) but A cannot wait for a network send and reply. In that case Thread 1 in machine A can put the data in a buffer, and wake up Thread 2 which sends the message.
It might also be the case that you want to use 2) and A can wait for B to reply, but it cannot tolerate waiting for B to reply a previous message. In this case, you can either use a thread pool in B, or you could do it with just two threads in B, one receives data and puts it in a buffer while thread the second processes the data.
The latter two examples require synchronization with mutexes and maybe condvars.
These methods only breaks down if 1) The rate that A receives data is slower that the rate at which B processes it, and 2) The available memory is not large enough to buffer the data before memory runs out. For this to happen you would probably need a fairly continuous stream of data. |
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