hello, Following is more of a criticism of Linux implementation of the Posix real-time extension of asynchronous I/O.... if not interesting please skip. The central data structure for Posix AIO is an aiocb. In any case, the Linux implementors added to the aiocb: /* Asynchronous I/O control block. */ struct aiocb { int aio_fildes; /* File desriptor. */ int aio_lio_opcode; /* Operation to be performed. */ int aio_reqprio; /* Request priority offset. */ volatile void *aio_buf; /* Location of buffer. */ size_t aio_nbytes; /* Length of transfer. */ struct sigevent aio_sigevent; /* Signal number and value. */ /* Internal members. */ <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< struct aiocb *__next_prio; int __abs_prio; int __policy; int __error_code; __ssize_t __return_value; #ifndef __USE_FILE_OFFSET64 __off_t aio_offset; /* File offset. */ char __pad[sizeof (__off64_t) - sizeof (__off_t)]; #else __off64_t aio_offset; /* File offset. */ #endif char __unused[32]; }; My viewpoint is that the above "Internal members" must be "carried" around in a Haskell program. Am I correct?? If I am correct, then the Linux implementation of Posix AIO is not portable to say Solaris? In hindsight, if I am correct, it seems that the Linux implementation of AIO should use the ordered pair (pid, fd) to reference the "internal" members and leave the "aiocb" "clean"? Very kind regards, Vasili