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NAME |
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Linux::AIO - linux-specific aio implemented using clone |
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|
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SYNOPSIS |
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use Linux::AIO; |
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|
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# This module has been mostly superseded by IO::AIO. |
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|
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DESCRIPTION |
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*This module has been mostly superseded by IO::AIO, which is API |
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compatible.* |
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|
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This module implements asynchronous I/O using the means available to |
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Linux - clone. It does not hook into the POSIX aio_* functions because |
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Linux does not yet support these in the kernel (even as of 2.6.12, only |
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O_DIRECT files are supported) and even if, it would only allow aio_read |
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and write, not open, stat and so on. |
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|
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Instead, in this module a number of (non-posix) threads are started that |
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execute your read/writes and signal their completion. You don't need |
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thread support in your libc or perl, and the threads created by this |
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module will not be visible to the pthreads library. |
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|
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NOTICE: the threads created by this module will automatically be killed |
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when the thread calling min_parallel exits. Make sure you only ever call |
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min_parallel from the same thread that loaded this module. |
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|
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Although the module will work with in the presence of other threads, it |
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is not reentrant, so use appropriate locking yourself. |
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API NOTES |
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All the "aio_*" calls are more or less thin wrappers around the syscall |
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with the same name (sans "aio_"). The arguments are similar or |
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identical, and they all accept an additional $callback argument which |
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must be a code reference. This code reference will get called with the |
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syscall return code (e.g. most syscalls return -1 on error, unlike perl, |
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which usually delivers "false") as it's sole argument when the given |
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syscall has been executed asynchronously. |
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|
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All functions that expect a filehandle will also accept a file |
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descriptor. |
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|
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The filenames you pass to these routines *must* be absolute. The reason |
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is that at the time the request is being executed, the current working |
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directory could have changed. Alternatively, you can make sure that you |
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never change the current working directory. |
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|
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Linux::AIO::min_parallel $nthreads |
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Set the minimum number of AIO threads to $nthreads. The default is |
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1, which means a single asynchronous operation can be done at one |
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time (the number of outstanding operations, however, is unlimited). |
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|
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It is recommended to keep the number of threads low, as some linux |
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kernel versions will scale negatively with the number of threads |
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(higher parallelity => MUCH higher latency). |
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|
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Under normal circumstances you don't need to call this function, as |
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this module automatically starts a single async thread. |
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|
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Linux::AIO::max_parallel $nthreads |
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Sets the maximum number of AIO threads to $nthreads. If more than |
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the specified number of threads are currently running, kill them. |
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This function blocks until the limit is reached. |
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|
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This module automatically runs "max_parallel 0" at program end, to |
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ensure that all threads are killed and that there are no outstanding |
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requests. |
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|
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Under normal circumstances you don't need to call this function. |
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|
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$fileno = Linux::AIO::poll_fileno |
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Return the *request result pipe filehandle*. This filehandle must be |
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polled for reading by some mechanism outside this module (e.g. Event |
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or select, see below). If the pipe becomes readable you have to call |
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"poll_cb" to check the results. |
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|
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See "poll_cb" for an example. |
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|
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Linux::AIO::poll_cb |
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Process all outstanding events on the result pipe. You have to call |
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this regularly. Returns the number of events processed. Returns |
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immediately when no events are outstanding. |
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|
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You can use Event to multiplex, e.g.: |
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|
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Event->io (fd => Linux::AIO::poll_fileno, |
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poll => 'r', async => 1, |
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cb => \&Linux::AIO::poll_cb); |
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|
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Linux::AIO::poll_wait |
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Wait till the result filehandle becomes ready for reading (simply |
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does a select on the filehandle. This is useful if you want to |
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synchronously wait for some requests to finish). |
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|
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See "nreqs" for an example. |
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|
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Linux::AIO::nreqs |
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Returns the number of requests currently outstanding. |
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Example: wait till there are no outstanding requests anymore: |
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|
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Linux::AIO::poll_wait, Linux::AIO::poll_cb |
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while Linux::AIO::nreqs; |
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|
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aio_open $pathname, $flags, $mode, $callback |
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Asynchronously open or create a file and call the callback with the |
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filedescriptor (NOT a perl filehandle, sorry for that, but watch |
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out, this might change in the future). |
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|
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The pathname passed to "aio_open" must be absolute. See API NOTES, |
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above, for an explanation. |
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|
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The $mode argument is a bitmask. See the "Fcntl" module for a list. |
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They are the same as used in "sysopen". |
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Example: |
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aio_open "/etc/passwd", O_RDONLY, 0, sub { |
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if ($_[0] >= 0) { |
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open my $fh, "<&=$_[0]"; |
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print "open successful, fh is $fh\n"; |
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... |
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} else { |
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die "open failed: $!\n"; |
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} |
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}; |
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aio_close $fh, $callback |
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Asynchronously close a file and call the callback with the result |
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code. |
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aio_read $fh,$offset,$length, $data,$dataoffset,$callback |
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aio_write $fh,$offset,$length, $data,$dataoffset,$callback |
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Reads or writes "length" bytes from the specified "fh" and "offset" |
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into the scalar given by "data" and offset "dataoffset" and calls |
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the callback without the actual number of bytes read (or -1 on |
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error, just like the syscall). |
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|
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Example: Read 15 bytes at offset 7 into scalar $buffer, strating at |
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offset 0 within the scalar: |
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aio_read $fh, 7, 15, $buffer, 0, sub { |
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$_[0] >= 0 or die "read error: $!"; |
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print "read <$buffer>\n"; |
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}; |
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|
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aio_readahead $fh,$offset,$length, $callback |
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Asynchronously reads the specified byte range into the page cache, |
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using the "readahead" syscall. |
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readahead() populates the page cache with data from a file so that |
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subsequent reads from that file will not block on disk I/O. The |
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$offset argument specifies the starting point from which data is to |
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be read and $length specifies the number of bytes to be read. I/O is |
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performed in whole pages, so that offset is effectively rounded down |
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to a page boundary and bytes are read up to the next page boundary |
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greater than or equal to (off-set+length). aio_readahead() does not |
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read beyond the end of the file. The current file offset of the file |
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is left unchanged. |
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aio_stat $fh_or_path, $callback |
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aio_lstat $fh, $callback |
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Works like perl's "stat" or "lstat" in void context. The callback |
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will be called after the stat and the results will be available |
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using "stat _" or "-s _" etc... |
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|
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The pathname passed to "aio_stat" must be absolute. See API NOTES, |
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above, for an explanation. |
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Currently, the stats are always 64-bit-stats, i.e. instead of |
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returning an error when stat'ing a large file, the results will be |
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silently truncated unless perl itself is compiled with large file |
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support. |
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|
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Example: Print the length of /etc/passwd: |
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aio_stat "/etc/passwd", sub { |
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$_[0] and die "stat failed: $!"; |
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print "size is ", -s _, "\n"; |
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}; |
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aio_unlink $pathname, $callback |
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Asynchronously unlink (delete) a file and call the callback with the |
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result code. |
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aio_fsync $fh, $callback |
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Asynchronously call fsync on the given filehandle and call the |
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callback with the fsync result code. |
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|
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aio_fdatasync $fh, $callback |
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Asynchronously call fdatasync on the given filehandle and call the |
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callback with the fdatasync result code. |
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|
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BUGS |
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This module has been extensively tested in a large and very busy |
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webserver for many years now. |
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|
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- aio_open gives a fd, but all other functions expect a perl filehandle. |
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|
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SEE ALSO |
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Coro, IO::AIO. |
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|
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AUTHOR |
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Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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