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passing strings between tasks

Posted by Dave S on December 10, 2008
What's the best way to pass strings between tasks?
1. xQueueCreate( maxstringlength, sizeof( char ) );
2. xQueueCreate( 1, maxstringlength ); //inefficient because it copies MAX string length instead of actual string length
3. xQueueCreate( 1, sizeof( char* ) ); //also requires semaphores
4. semaphores around a global string?


RE: passing strings between tasks

Posted by dave m on December 10, 2008
Depends whether the receiving task needs to modify the string, and whether the sending task needs its own copy, or needs to release the memory or whatever. For strings that are const after sending (no task needs to modify or delete them), I'd go with 3. If you're really trying to pass a buffer of data from a producer to a consumer (for example), and have the producer generate more data after the consumer is finished, then I'd go with 4: semaphores around a global buffer.

RE: passing strings between tasks

Posted by Dave S on December 10, 2008
Thx Dave.
4 it is.
The producer is generating variable sized non-const 'debug' strings that are output to a port by the consumer.

RE: passing strings between tasks

Posted by dave m on December 10, 2008
Oh yeah, totally. That's a great way to handle debugging output (everything spews into a common circular buffer, and some low-priority task prints it out when it has a chance). It can get pretty complex if you're doing timestamping and making sure messages interleave on a line-by-line basis, plus the buffer has to be pretty big if you have a lot of high-priority output, but a robust debug/error reporting scheme makes development MUCH easier.

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