… | |
… | |
428 | reading at byte offset C<$in_offset>, and starts writing at the current |
428 | reading at byte offset C<$in_offset>, and starts writing at the current |
429 | file offset of C<$out_fh>. Because of that, it is not safe to issue more |
429 | file offset of C<$out_fh>. Because of that, it is not safe to issue more |
430 | than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each |
430 | than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each |
431 | other. |
431 | other. |
432 | |
432 | |
|
|
433 | Please note that C<aio_sendfile> can read more bytes from C<$in_fh> than |
|
|
434 | are written, and there is no way to find out how many bytes have been read |
|
|
435 | from C<aio_sendfile> alone, as C<aio_sendfile> only provides the number of |
|
|
436 | bytes written to C<$out_fh>. Only if the result value equals C<$length> |
|
|
437 | one can assume that C<$length> bytes have been read. |
|
|
438 | |
|
|
439 | Unlike with other C<aio_> functions, it makes a lot of sense to use |
|
|
440 | C<aio_sendfile> on non-blocking sockets, as long as one end (typically |
|
|
441 | the C<$in_fh>) is a file - the file I/O will then be asynchronous, while |
|
|
442 | the socket I/O will be non-blocking. Note, however, that you can run into |
|
|
443 | a trap where C<aio_sendfile> reads some data with readahead, then fails |
|
|
444 | to write all data, and when the socket is ready the next time, the data |
|
|
445 | in the cache is already lost, forcing C<aio_sendfile> to again hit the |
|
|
446 | disk. Explicit C<aio_read> + C<aio_write> let's you control resource usage |
|
|
447 | much better. |
|
|
448 | |
433 | This call tries to make use of a native C<sendfile> syscall to provide |
449 | This call tries to make use of a native C<sendfile> syscall to provide |
434 | zero-copy operation. For this to work, C<$out_fh> should refer to a |
450 | zero-copy operation. For this to work, C<$out_fh> should refer to a |
435 | socket, and C<$in_fh> should refer to an mmap'able file. |
451 | socket, and C<$in_fh> should refer to an mmap'able file. |
436 | |
452 | |
437 | If a native sendfile cannot be found or it fails with C<ENOSYS>, |
453 | If a native sendfile cannot be found or it fails with C<ENOSYS>, |
438 | C<ENOTSUP>, C<EOPNOTSUPP>, C<EAFNOSUPPORT>, C<EPROTOTYPE> or C<ENOTSOCK>, |
454 | C<ENOTSUP>, C<EOPNOTSUPP>, C<EAFNOSUPPORT>, C<EPROTOTYPE> or C<ENOTSOCK>, |
439 | it will be emulated, so you can call C<aio_sendfile> on any type of |
455 | it will be emulated, so you can call C<aio_sendfile> on any type of |
440 | filehandle regardless of the limitations of the operating system. |
456 | filehandle regardless of the limitations of the operating system. |
441 | |
|
|
442 | Please note, however, that C<aio_sendfile> can read more bytes from |
|
|
443 | C<$in_fh> than are written, and there is no way to find out how many |
|
|
444 | bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only |
|
|
445 | provides the number of bytes written to C<$out_fh>. Only if the result |
|
|
446 | value equals C<$length> one can assume that C<$length> bytes have been |
|
|
447 | read. |
|
|
448 | |
457 | |
449 | |
458 | |
450 | =item aio_readahead $fh,$offset,$length, $callback->($retval) |
459 | =item aio_readahead $fh,$offset,$length, $callback->($retval) |
451 | |
460 | |
452 | C<aio_readahead> populates the page cache with data from a file so that |
461 | C<aio_readahead> populates the page cache with data from a file so that |