7.14 Concurrent Input and Output

Reading from or writing to a file descriptor may block, since buffers my be empty or resp. full. Thus calling read or write might block the whole Oz process. We therefore provide abstractions that allow concurrent access to file descriptors from within the C level.

We first declare an abstact type OZ_IOHandler which is a function expecting an integer and an arbitrary pointer:

   typedef int OZ_IOHandler(int, void *);

The user can then use the following abstractions:

OZ_registerReadHandler

void OZ_registerReadHandler(int fd,OZ_IOHandler fun,void *args)

Registers fun as a read handler for file descriptor fd. Any previously registered function will be overridden. When input gets available on fd then fun(fd,args) will be called by the Oz scheduler. The usage of args provides a way to pass arbitrary arguments to fun.

OZ_unregisterRead

void OZ_unregisterRead(int fd)

Unregisters a previously registered read handler for file descriptor fd.

OZ_registerWriteHandler

void OZ_registerWriteHandler(int fd,OZ_IOHandler fun,void *args)

Analogously to OZ_registerReadHandler for writing. fun is called as soon as the output buffer for fd gets empty.

OZ_unregisterWrite

void OZ_unregisterWrite(int fd)

Unregisters a previously registered write handler for file descriptor fd.