threads synchronization

Question

i want to create a thread that reads from a file into a buffer and another thread that would write from the buffer into another file. how to make sure that read thread has read some bytes before writing from the buffer, and how to make sure that write thread has wrote the data in the buffer before reading in new data.

shellno10 · Answer

it's just a byte array i want to be able to read and write in parallel but spawning a new thread every for every write from the read loop, won't that create much overheard ? I tried: Monitor.Enter(buffer); Monitor.Wait(buffer); bytes = read.Read(buffer, 0, buffer.Length); Monitor.Pulse(buffer); in the read thread and: Monitor.Enter(buffer); Monitor.Wait(buffer); bytes = read.Read(buffer, 0, buffer.Length); Monitor.Pulse(buffer); in the write thread but it didn't work, the program just locks and nothing is written to the file also i need to detect end of file in order to stop the read loop i caught the System.IO.EndOfStreamException exception but i dunno if that'll work

spgilmore · Answer

How is your buffer constructed, exactly? Is it a byte array or some other static container that you fill once, write once, fill, write, fill, write, etc? Or is it something more dynamic like a node queue? I would recommend a queue. It is ideal for this sort of purpose. It is designed to easily add new items as they come in, and discard finished items as they are completed. It maintains order, and it is easy to determine if there is data to write. Just check the queue size. The queue needs to be visible from both threads. There is lots of information about queues. STW and consult the help on the Queue class. Just read a byte array of 512 bytes at a time, then add that byte array as an object to the queue (.Enqueue())in the reader thread. In the writer thread, just .Dequeue() the object and cast it back to a byte array and write the bytes. The writer only needs to check the Queue.Count>0 to make sure there is data to be written. There are two ways that this could be done. The first involves a third thread, probably your main application thread. This would make synchronization a little more complex. I would instead recommend that the reader thread spawn the writer thread and join with it when it's done. This would be a nice encapsulation of the operation as a whole.

threads synchronization

Answers (2)