Blocked Streaming Class with Semaphore in delphi

Question

I am working on a class in delphi for blocked streaming of data. The class has two methods to read and write to the stream. Method "Write", will add new data into the buffer and method "read", will pop some data out of the buffer:

TBlockingStream = class
public
  function Write(const data; size: Integer): Integer;
  function Read(var data; size: Integer): Integer;
  ...
end;

Size of input and output data would varies each time we write/read new data to/from the stream. I want that method "read" waits until the requested size is provided by method "write". Using Semaphore to syncing, in the method "write", I release semaphore (ReleaseSemaphore function) with the number of bytes written to the buffer, but in the method "read" I do not know how to wait for the number of bytes which is requested in the method "read"?

Answer 1

You can try to call OpenSemaphore() Size times and use WaitForMultipleObjectsEx() to wait for all these handles. Although not sure that this will work.

More suitable solution is to maintain a volatile (thread-safe) count of bytes available by using critical section or interlocked functions to modify and check the count. In case of use more efficient interlocked functions ABA problem should be considered and handled properly.

To avoid unnecessary looping in Read() TEvent can be used.