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condition variables and mutexes


Are the mutexes used with condition variables customarily used for
synchronization with other consumer threads only, or does the producer
thread use the mutexes as well?

I would imagine that the producer thread would generally not use the
mutex associated with a condition variable.  I would think that if a
mutex is needed, I should probably create a separate one for my use,
right?

Do I even care about the mutex associated with the condition variable if
I only have one consumer, and one producer?


Here's my situation in particular.

I've created a circular buffer that will hold three times the amount of
data required for each cycle.  Cycles usually occur once every second.
I've created three condition/mutex variable pairs for each of the three
slots in the circular buffer.  

Producer thread
- fill the first slot of the buffer with the data, and signal the
consumer thread  (condition 1)  
- fill the second slot of the buffer with the data, and signal the
consumer thread (condition 2)
- fill the third slot of the buffer with the data, and signal the
consumer thread  (condition 3)

Consumer thread
loop indefinately
- wait for signal 1
  - COPY data to another buffer
  - do something with data
- wait for signal 2
  - COPY data to another buffer
  - do something with data
- wait for signal 3
  - COPY data to another buffer
  - do something with data

I need a way of making sure that the head pointer of the circular buffer
doesn't change to point to the next slot before the consumer thread has
copied it.  I was thinking of using a mutex for this purpose.

Trenton D. Adams
Extreme Engineering
#17, 6025 - 12 St. SE
Calgary, Alberta, Canada
T2H 2K1

Phone: 403 640 9494 ext-208
Fax: 403 640 9599

http://www.extremeeng.com


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