Named Pipe Buffer Size

• Microsoft Win32 Application Programming Interface (API) included with:

      - Microsoft Windows NT versions 3.1, 3.5, 3.51, and 4.0
  

The documentation for CreateNamedPipe() indicates that

   The input and output buffer sizes are advisory. The actual buffer
   size reserved for each end of the named pipe is either the system
   default, the system minimum or maximum, or the specified size
   rounded up to the next allocation boundary.

Every time a named pipe is created, the system creates the inbound and/or outbound buffers using nonpaged pool, which is the physical memory used by the kernel. The number of pipe instances (as well as objects such as threads and processes) that you can create is limited by the available nonpaged pool. Each read or write request requires space in the buffer for the read or write data, plus additional space for the internal data structures.

Whenever a pipe write operation occurs, the system first tries to charge the memory against the pipe write quota. If the remaining pipe write quota is enough to fulfill the request, the write completes immediately.

If the remaining pipe write quota is too small to fulfill the request, the system will try to expand the buffers to accommodate the data using nonpaged pool reserved for the process. The write will block until the data is read from the pipe so that the additional buffer quota can be released. Therefore, if your specified buffer size is too small, the system will grow the buffer as needed, but the downside is that the operation will block. If the operation is overlapped, a system thread is blocked; otherwise, the application thread is blocked.