# Module Netsys_polypipe

    module Netsys_polypipe: sig .. end

Polymorphic message pipes

These pipes are restricted to a single process, and can be used to send messages of any types between threads.

    exception Closed

    type 'a polypipe

    val create : int -> 'a polypipe * 'a polypipe

Create a new polypipe with an internal buffer of n messages. The left descriptor is open for reading, and the right is open for writing.

    val length : 'a polypipe -> int

return the number of messages in the buffer

    val eof : 'a polypipe -> bool

whether the eof marker was sent. Note that there may still be messages in the buffer

    val read : nonblock:bool -> 'a polypipe -> 'a option

read a message. `None` means EOF. Possible `Unix.unix_error` codes:

- `EAGAIN`: the pipe is non-blocking, and there is no message in the buffer
- `EINTR`: a signal arrived

Raises `Closed` if the polypipe has been closed.

    val write : nonblock:bool -> 'a polypipe -> 'a option -> unit

write a message, or mark the end of the stream (`None`). Possible `Unix.unix_error` codes:

- `EAGAIN`: the pipe is non-blocking, and there is no message in the buffer
- `EINTR`: a signal arrived
- `EPIPE`: it was tried to send a message after sending `None`.

Unlike OS pipes, polypipes become writable after signaling EOF.

Raises `Closed` if the polypipe has been closed.

    val close : 'a polypipe -> unit

Close the pipe. Writing will be immediately impossible. Reading will return `None`.

    val set_read_notify : 'a polypipe -> (unit -> unit) -> unit

`set_read_notify pipe f`: Sets that the function `f` is called when the pipe becomes readable (or reaches eof). Only one such function can be registered; any previous function is overwritten. The function will be called from a different thread.

    val set_write_notify : 'a polypipe -> (unit -> unit) -> unit

`set_write_notify pipe f`: Sets that the function `f` is called when the pipe becomes writable (or reaches eof). Only one such function can be registered; any previous function is overwritten. The function will be called from a different thread.

    val read_descr : 'a polypipe -> Unix.file_descr

Returns a descriptor that can be used for polling. When the descriptor is readable there is a message in the buffer. If called several times, always the same descriptor is returned.

The caller has to close the descriptor after use.

Raises `Closed` if the polypipe has been closed.

    val write_descr : 'a polypipe -> Unix.file_descr

Returns a descriptor that can be used for polling. When the descriptor is readable (sic) there is space in the buffer for another message. If called several times, always the same descriptor is returned.

The caller has to close the descriptor after use.

Raises `Closed` if the polypipe has been closed.

    val set_exception : 'a polypipe -> exn -> unit

Sets an exception that is returned by further calls of `write`. If an exception already exists, it is not overwritten.

`read` will return EOF. Readers need to test for the exceptionw with `get_exception`.

    val get_exception : 'a polypipe -> exn option

Get the exception

## Debugging

    module Debug: sig .. end