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NAME |
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IO::AIO - Asynchronous Input/Output |
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|
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SYNOPSIS |
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use IO::AIO; |
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|
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aio_open "/etc/passwd", O_RDONLY, 0, sub { |
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my ($fh) = @_; |
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... |
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}; |
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|
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aio_unlink "/tmp/file", sub { }; |
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|
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aio_read $fh, 30000, 1024, $buffer, 0, sub { |
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$_[0] > 0 or die "read error: $!"; |
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}; |
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|
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# AnyEvent |
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open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!"; |
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my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb }); |
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|
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# Event |
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Event->io (fd => IO::AIO::poll_fileno, |
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poll => 'r', |
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cb => \&IO::AIO::poll_cb); |
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|
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# Glib/Gtk2 |
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add_watch Glib::IO IO::AIO::poll_fileno, |
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in => sub { IO::AIO::poll_cb; 1 }; |
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|
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# Tk |
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Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "", |
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readable => \&IO::AIO::poll_cb); |
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|
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# Danga::Socket |
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Danga::Socket->AddOtherFds (IO::AIO::poll_fileno => |
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\&IO::AIO::poll_cb); |
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|
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DESCRIPTION |
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This module implements asynchronous I/O using whatever means your |
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operating system supports. |
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|
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Currently, a number of threads are started that execute your read/writes |
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and signal their completion. You don't need thread support in your libc |
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or perl, and the threads created by this module will not be visible to |
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the pthreads library. In the future, this module might make use of the |
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native aio functions available on many operating systems. However, they |
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are often not well-supported (Linux doesn't allow them on normal files |
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currently, for example), and they would only support aio_read and |
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aio_write, so the remaining functionality would have to be implemented |
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using threads anyway. |
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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 currently not reentrant, so use appropriate locking yourself, always |
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call "poll_cb" from within the same thread, or never call "poll_cb" (or |
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other "aio_" functions) recursively. |
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|
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FUNCTIONS |
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AIO FUNCTIONS |
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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 (and optional) $callback |
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argument which must be a code reference. This code reference will get |
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called with the syscall return code (e.g. most syscalls return -1 on |
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error, unlike perl, which usually delivers "false") as it's sole |
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argument when the given syscall has been executed asynchronously. |
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|
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All functions expecting a filehandle keep a copy of the filehandle |
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internally until the request has finished. |
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|
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The pathnames you pass to these routines *must* be absolute and encoded |
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in byte form. The reason for the former is that at the time the request |
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is being executed, the current working directory could have changed. |
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Alternatively, you can make sure that you never change the current |
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working directory. |
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|
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To encode pathnames to byte form, either make sure you either: a) always |
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pass in filenames you got from outside (command line, readdir etc.), b) |
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are ASCII or ISO 8859-1, c) use the Encode module and encode your |
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pathnames to the locale (or other) encoding in effect in the user |
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environment, d) use Glib::filename_from_unicode on unicode filenames or |
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e) use something else. |
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|
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aio_open $pathname, $flags, $mode, $callback->($fh) |
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Asynchronously open or create a file and call the callback with a |
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newly created filehandle for the file. |
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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 $flags argument is a bitmask. See the "Fcntl" module for a list. |
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They are the same as used by "sysopen". |
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|
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Likewise, $mode specifies the mode of the newly created file, if it |
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didn't exist and "O_CREAT" has been given, just like perl's |
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"sysopen", except that it is mandatory (i.e. use 0 if you don't |
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create new files, and 0666 or 0777 if you do). |
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|
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Example: |
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|
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aio_open "/etc/passwd", O_RDONLY, 0, sub { |
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if ($_[0]) { |
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print "open successful, fh is $_[0]\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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|
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aio_close $fh, $callback->($status) |
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Asynchronously close a file and call the callback with the result |
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code. *WARNING:* although accepted, you should not pass in a perl |
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filehandle here, as perl will likely close the file descriptor |
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another time when the filehandle is destroyed. Normally, you can |
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safely call perls "close" or just let filehandles go out of scope. |
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|
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This is supposed to be a bug in the API, so that might change. It's |
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therefore best to avoid this function. |
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|
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aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval) |
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aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval) |
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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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The $data scalar *MUST NOT* be modified in any way while the request |
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is outstanding. Modifying it can result in segfaults or WW3 (if the |
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necessary/optional hardware is installed). |
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|
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Example: Read 15 bytes at offset 7 into scalar $buffer, starting at |
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offset 0 within the scalar: |
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|
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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 $_[0] bytes: <$buffer>\n"; |
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}; |
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|
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aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval) |
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Tries to copy $length bytes from $in_fh to $out_fh. It starts |
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reading at byte offset $in_offset, and starts writing at the current |
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file offset of $out_fh. Because of that, it is not safe to issue |
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more than one "aio_sendfile" per $out_fh, as they will interfere |
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with each other. |
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|
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This call tries to make use of a native "sendfile" syscall to |
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provide zero-copy operation. For this to work, $out_fh should refer |
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to a socket, and $in_fh should refer to mmap'able file. |
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|
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If the native sendfile call fails or is not implemented, it will be |
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emulated, so you can call "aio_sendfile" on any type of filehandle |
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regardless of the limitations of the operating system. |
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|
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Please note, however, that "aio_sendfile" can read more bytes from |
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$in_fh than are written, and there is no way to find out how many |
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bytes have been read from "aio_sendfile" alone, as "aio_sendfile" |
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only provides the number of bytes written to $out_fh. Only if the |
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result value equals $length one can assume that $length bytes have |
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been read. |
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|
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aio_readahead $fh,$offset,$length, $callback->($retval) |
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"aio_readahead" populates the page cache with data from a file so |
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that 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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|
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If that syscall doesn't exist (likely if your OS isn't Linux) it |
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will be emulated by simply reading the data, which would have a |
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similar effect. |
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|
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aio_stat $fh_or_path, $callback->($status) |
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aio_lstat $fh, $callback->($status) |
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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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|
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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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|
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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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|
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aio_unlink $pathname, $callback->($status) |
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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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|
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aio_rmdir $pathname, $callback->($status) |
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Asynchronously rmdir (delete) a directory and call the callback with |
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the result code. |
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|
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aio_readdir $pathname, $callback->($entries) |
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Unlike the POSIX call of the same name, "aio_readdir" reads an |
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entire directory (i.e. opendir + readdir + closedir). The entries |
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will not be sorted, and will NOT include the "." and ".." entries. |
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|
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The callback a single argument which is either "undef" or an |
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array-ref with the filenames. |
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|
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aio_scandir $path, $maxreq, $callback->($dirs, $nondirs) |
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Scans a directory (similar to "aio_readdir") and tries to separate |
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the entries of directory $path into two sets of names, ones you can |
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recurse into (directories), and ones you cannot recurse into |
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(everything else). |
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|
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"aio_scandir" is a composite request that consists of many |
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aio-primitives. $maxreq specifies the maximum number of outstanding |
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aio requests that this function generates. If it is "<= 0", then a |
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suitable default will be chosen (currently 8). |
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|
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On error, the callback is called without arguments, otherwise it |
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receives two array-refs with path-relative entry names. |
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|
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Example: |
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|
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aio_scandir $dir, 0, sub { |
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my ($dirs, $nondirs) = @_; |
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print "real directories: @$dirs\n"; |
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print "everything else: @$nondirs\n"; |
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}; |
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|
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Implementation notes. |
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|
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The "aio_readdir" cannot be avoided, but "stat()"'ing every entry |
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can. |
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|
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After reading the directory, the modification time, size etc. of the |
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directory before and after the readdir is checked, and if they |
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match, the link count will be used to decide how many entries are |
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directories (if >= 2). Otherwise, no knowledge of the number of |
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subdirectories will be assumed. |
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|
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Then entires will be sorted into likely directories (everything |
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without a non-initial dot) and likely non-directories (everything |
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else). Then every entry + "/." will be "stat"'ed, likely directories |
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first. This is often faster because filesystems might detect the |
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type of the entry without reading the inode data (e.g. ext2fs |
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filetype feature). If that succeeds, it assumes that the entry is a |
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directory or a symlink to directory (which will be checked |
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seperately). |
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|
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If the known number of directories has been reached, the rest of the |
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entries is assumed to be non-directories. |
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|
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aio_fsync $fh, $callback->($status) |
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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, $callback->($status) |
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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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If this call isn't available because your OS lacks it or it couldn't |
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be detected, it will be emulated by calling "fsync" instead. |
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|
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SUPPORT FUNCTIONS |
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$fileno = IO::AIO::poll_fileno |
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Return the *request result pipe file descriptor*. This filehandle |
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must be polled for reading by some mechanism outside this module |
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(e.g. Event or select, see below or the SYNOPSIS). If the pipe |
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becomes readable you have to call "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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IO::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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Example: Install an Event watcher that automatically calls |
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IO::AIO::poll_cb with high priority: |
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|
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Event->io (fd => IO::AIO::poll_fileno, |
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poll => 'r', async => 1, |
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cb => \&IO::AIO::poll_cb); |
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|
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IO::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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IO::AIO::nreqs |
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Returns the number of requests currently outstanding (i.e. for which |
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their callback has not been invoked yet). |
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|
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Example: wait till there are no outstanding requests anymore: |
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|
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IO::AIO::poll_wait, IO::AIO::poll_cb |
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while IO::AIO::nreqs; |
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|
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IO::AIO::flush |
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Wait till all outstanding AIO requests have been handled. |
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|
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Strictly equivalent to: |
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|
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IO::AIO::poll_wait, IO::AIO::poll_cb |
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while IO::AIO::nreqs; |
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|
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IO::AIO::poll |
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Waits until some requests have been handled. |
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|
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Strictly equivalent to: |
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|
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IO::AIO::poll_wait, IO::AIO::poll_cb |
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if IO::AIO::nreqs; |
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|
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IO::AIO::min_parallel $nthreads |
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Set the minimum number of AIO threads to $nthreads. The current |
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default is 4, which means four asynchronous operations can be done |
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at one time (the number of outstanding operations, however, is |
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unlimited). |
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|
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IO::AIO starts threads only on demand, when an AIO request is queued |
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and no free thread exists. |
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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). With current Linux 2.6 |
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versions, 4-32 threads should be fine. |
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|
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Under most circumstances you don't need to call this function, as |
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the module selects a default that is suitable for low to moderate |
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load. |
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|
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IO::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, this function |
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kills them. This function blocks until the limit is reached. |
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|
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While $nthreads are zero, aio requests get queued but not executed |
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until the number of threads has been increased again. |
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|
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This module automatically runs "max_parallel 0" at program end, to |
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ensure that all threads are killed and that there are no outstanding |
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requests. |
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|
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Under normal circumstances you don't need to call this function. |
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|
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$oldnreqs = IO::AIO::max_outstanding $nreqs |
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Sets the maximum number of outstanding requests to $nreqs. If you |
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try to queue up more than this number of requests, the caller will |
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block until some requests have been handled. |
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|
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The default is very large, so normally there is no practical limit. |
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If you queue up many requests in a loop it often improves speed if |
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you set this to a relatively low number, such as 100. |
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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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FORK BEHAVIOUR |
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Before the fork, IO::AIO enters a quiescent state where no requests can |
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be added in other threads and no results will be processed. After the |
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fork the parent simply leaves the quiescent state and continues |
| 369 |
request/result processing, while the child clears the request/result |
| 370 |
queue (so the requests started before the fork will only be handled in |
| 371 |
the parent). Threats will be started on demand until the limit ste in |
| 372 |
the parent process has been reached again. |
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|
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SEE ALSO |
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Coro, Linux::AIO. |
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|
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AUTHOR |
| 378 |
Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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|
