--- IO-AIO/README 2006/06/26 14:53:55 1.17 +++ IO-AIO/README 2006/10/26 16:28:33 1.18 @@ -15,24 +15,34 @@ $_[0] > 0 or die "read error: $!"; }; - # AnyEvent + # version 2+ has request and group objects + use IO::AIO 2; + + aioreq_pri 4; # give next request a very high priority + my $req = aio_unlink "/tmp/file", sub { }; + $req->cancel; # cancel request if still in queue + + my $grp = aio_group sub { print "all stats done\n" }; + add $grp aio_stat "..." for ...; + + # AnyEvent integration open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!"; my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb }); - # Event + # Event integration Event->io (fd => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb); - # Glib/Gtk2 + # Glib/Gtk2 integration add_watch Glib::IO IO::AIO::poll_fileno, in => sub { IO::AIO::poll_cb; 1 }; - # Tk + # Tk integration Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "", readable => \&IO::AIO::poll_cb); - # Danga::Socket + # Danga::Socket integration Danga::Socket->AddOtherFds (IO::AIO::poll_fileno => \&IO::AIO::poll_cb); @@ -40,371 +50,718 @@ This module implements asynchronous I/O using whatever means your operating system supports. - Currently, a number of threads are started that execute your read/writes - and signal their completion. You don't need thread support in your libc - or perl, and the threads created by this module will not be visible to - the pthreads library. In the future, this module might make use of the - native aio functions available on many operating systems. However, they - are often not well-supported (Linux doesn't allow them on normal files - currently, for example), and they would only support aio_read and + In this version, a number of threads are started that execute your + requests and signal their completion. You don't need thread support in + perl, and the threads created by this module will not be visible to + perl. In the future, this module might make use of the native aio + functions available on many operating systems. However, they are often + not well-supported or restricted (Linux doesn't allow them on normal + files currently, for example), and they would only support aio_read and aio_write, so the remaining functionality would have to be implemented using threads anyway. - Although the module will work with in the presence of other threads, it - is currently not reentrant, so use appropriate locking yourself, always - call "poll_cb" from within the same thread, or never call "poll_cb" (or - other "aio_" functions) recursively. + Although the module will work with in the presence of other (Perl-) + threads, it is currently not reentrant in any way, so use appropriate + locking yourself, always call "poll_cb" from within the same thread, or + never call "poll_cb" (or other "aio_" functions) recursively. + +REQUEST ANATOMY AND LIFETIME + Every "aio_*" function creates a request. which is a C data structure + not directly visible to Perl. + + If called in non-void context, every request function returns a Perl + object representing the request. In void context, nothing is returned, + which saves a bit of memory. + + The perl object is a fairly standard ref-to-hash object. The hash + contents are not used by IO::AIO so you are free to store anything you + like in it. + + During their existance, aio requests travel through the following + states, in order: + + ready + Immediately after a request is created it is put into the ready + state, waiting for a thread to execute it. + + execute + A thread has accepted the request for processing and is currently + executing it (e.g. blocking in read). + + pending + The request has been executed and is waiting for result processing. + + While request submission and execution is fully asynchronous, result + processing is not and relies on the perl interpreter calling + "poll_cb" (or another function with the same effect). + + result + The request results are processed synchronously by "poll_cb". + + The "poll_cb" function will process all outstanding aio requests by + calling their callbacks, freeing memory associated with them and + managing any groups they are contained in. + + done + Request has reached the end of its lifetime and holds no resources + anymore (except possibly for the Perl object, but its connection to + the actual aio request is severed and calling its methods will + either do nothing or result in a runtime error). FUNCTIONS AIO FUNCTIONS - All the "aio_*" calls are more or less thin wrappers around the syscall - with the same name (sans "aio_"). The arguments are similar or - identical, and they all accept an additional (and optional) $callback - argument which must be a code reference. This code reference will get - called with the syscall return code (e.g. most syscalls return -1 on - error, unlike perl, which usually delivers "false") as it's sole - argument when the given syscall has been executed asynchronously. - - All functions expecting a filehandle keep a copy of the filehandle - internally until the request has finished. - - The pathnames you pass to these routines *must* be absolute and encoded - in byte form. The reason for the former is that at the time the request - is being executed, the current working directory could have changed. - Alternatively, you can make sure that you never change the current - working directory. - - To encode pathnames to byte form, either make sure you either: a) always - pass in filenames you got from outside (command line, readdir etc.), b) - are ASCII or ISO 8859-1, c) use the Encode module and encode your - pathnames to the locale (or other) encoding in effect in the user - environment, d) use Glib::filename_from_unicode on unicode filenames or - e) use something else. - - aio_open $pathname, $flags, $mode, $callback->($fh) - Asynchronously open or create a file and call the callback with a - newly created filehandle for the file. - - The pathname passed to "aio_open" must be absolute. See API NOTES, - above, for an explanation. - - The $flags argument is a bitmask. See the "Fcntl" module for a list. - They are the same as used by "sysopen". - - Likewise, $mode specifies the mode of the newly created file, if it - didn't exist and "O_CREAT" has been given, just like perl's - "sysopen", except that it is mandatory (i.e. use 0 if you don't - create new files, and 0666 or 0777 if you do). - - Example: - - aio_open "/etc/passwd", O_RDONLY, 0, sub { - if ($_[0]) { - print "open successful, fh is $_[0]\n"; - ... - } else { - die "open failed: $!\n"; - } - }; + All the "aio_*" calls are more or less thin wrappers around the + syscall with the same name (sans "aio_"). The arguments are similar + or identical, and they all accept an additional (and optional) + $callback argument which must be a code reference. This code + reference will get called with the syscall return code (e.g. most + syscalls return -1 on error, unlike perl, which usually delivers + "false") as it's sole argument when the given syscall has been + executed asynchronously. + + All functions expecting a filehandle keep a copy of the filehandle + internally until the request has finished. + + All requests return objects of type IO::AIO::REQ that allow further + manipulation of those requests while they are in-flight. + + The pathnames you pass to these routines *must* be absolute and + encoded in byte form. The reason for the former is that at the time + the request is being executed, the current working directory could + have changed. Alternatively, you can make sure that you never change + the current working directory. + + To encode pathnames to byte form, either make sure you either: a) + always pass in filenames you got from outside (command line, readdir + etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and + encode your pathnames to the locale (or other) encoding in effect in + the user environment, d) use Glib::filename_from_unicode on unicode + filenames or e) use something else. + + $prev_pri = aioreq_pri [$pri] + Returns the priority value that would be used for the next + request and, if $pri is given, sets the priority for the next + aio request. + + The default priority is 0, the minimum and maximum priorities + are -4 and 4, respectively. Requests with higher priority will + be serviced first. + + The priority will be reset to 0 after each call to one of the + "aio_*" functions. + + Example: open a file with low priority, then read something from + it with higher priority so the read request is serviced before + other low priority open requests (potentially spamming the + cache): + + aioreq_pri -3; + aio_open ..., sub { + return unless $_[0]; + + aioreq_pri -2; + aio_read $_[0], ..., sub { + ... + }; + }; + + aioreq_nice $pri_adjust + Similar to "aioreq_pri", but subtracts the given value from the + current priority, so effects are cumulative. + + aio_open $pathname, $flags, $mode, $callback->($fh) + Asynchronously open or create a file and call the callback with + a newly created filehandle for the file. + + The pathname passed to "aio_open" must be absolute. See API + NOTES, above, for an explanation. + + The $flags argument is a bitmask. See the "Fcntl" module for a + list. They are the same as used by "sysopen". + + Likewise, $mode specifies the mode of the newly created file, if + it didn't exist and "O_CREAT" has been given, just like perl's + "sysopen", except that it is mandatory (i.e. use 0 if you don't + create new files, and 0666 or 0777 if you do). + + Example: + + aio_open "/etc/passwd", O_RDONLY, 0, sub { + if ($_[0]) { + print "open successful, fh is $_[0]\n"; + ... + } else { + die "open failed: $!\n"; + } + }; + + aio_close $fh, $callback->($status) + Asynchronously close a file and call the callback with the + result code. *WARNING:* although accepted, you should not pass + in a perl filehandle here, as perl will likely close the file + descriptor another time when the filehandle is destroyed. + Normally, you can safely call perls "close" or just let + filehandles go out of scope. + + This is supposed to be a bug in the API, so that might change. + It's therefore best to avoid this function. + + aio_read $fh,$offset,$length, $data,$dataoffset, + $callback->($retval) + aio_write $fh,$offset,$length, $data,$dataoffset, + $callback->($retval) + Reads or writes "length" bytes from the specified "fh" and + "offset" into the scalar given by "data" and offset "dataoffset" + and calls the callback without the actual number of bytes read + (or -1 on error, just like the syscall). + + The $data scalar *MUST NOT* be modified in any way while the + request is outstanding. Modifying it can result in segfaults or + WW3 (if the necessary/optional hardware is installed). + + Example: Read 15 bytes at offset 7 into scalar $buffer, starting + at offset 0 within the scalar: + + aio_read $fh, 7, 15, $buffer, 0, sub { + $_[0] > 0 or die "read error: $!"; + print "read $_[0] bytes: <$buffer>\n"; + }; + + aio_move $srcpath, $dstpath, $callback->($status) + Try to move the *file* (directories not supported as either + source or destination) from $srcpath to $dstpath and call the + callback with the 0 (error) or -1 ok. + + This is a composite request that tries to rename(2) the file + first. If rename files with "EXDEV", it creates the destination + file with mode 0200 and copies the contents of the source file + into it using "aio_sendfile", followed by restoring atime, + mtime, access mode and uid/gid, in that order, and unlinking the + $srcpath. + + If an error occurs, the partial destination file will be + unlinked, if possible, except when setting atime, mtime, access + mode and uid/gid, where errors are being ignored. + + aio_sendfile $out_fh, $in_fh, $in_offset, $length, + $callback->($retval) + Tries to copy $length bytes from $in_fh to $out_fh. It starts + reading at byte offset $in_offset, and starts writing at the + current file offset of $out_fh. Because of that, it is not safe + to issue more than one "aio_sendfile" per $out_fh, as they will + interfere with each other. + + This call tries to make use of a native "sendfile" syscall to + provide zero-copy operation. For this to work, $out_fh should + refer to a socket, and $in_fh should refer to mmap'able file. + + If the native sendfile call fails or is not implemented, it will + be emulated, so you can call "aio_sendfile" on any type of + filehandle regardless of the limitations of the operating + system. + + Please note, however, that "aio_sendfile" can read more bytes + from $in_fh than are written, and there is no way to find out + how many bytes have been read from "aio_sendfile" alone, as + "aio_sendfile" only provides the number of bytes written to + $out_fh. Only if the result value equals $length one can assume + that $length bytes have been read. + + aio_readahead $fh,$offset,$length, $callback->($retval) + "aio_readahead" populates the page cache with data from a file + so that subsequent reads from that file will not block on disk + I/O. The $offset argument specifies the starting point from + which data is to be read and $length specifies the number of + bytes to be read. I/O is performed in whole pages, so that + offset is effectively rounded down to a page boundary and bytes + are read up to the next page boundary greater than or equal to + (off-set+length). "aio_readahead" does not read beyond the end + of the file. The current file offset of the file is left + unchanged. + + If that syscall doesn't exist (likely if your OS isn't Linux) it + will be emulated by simply reading the data, which would have a + similar effect. + + aio_stat $fh_or_path, $callback->($status) + aio_lstat $fh, $callback->($status) + Works like perl's "stat" or "lstat" in void context. The + callback will be called after the stat and the results will be + available using "stat _" or "-s _" etc... + + The pathname passed to "aio_stat" must be absolute. See API + NOTES, above, for an explanation. + + Currently, the stats are always 64-bit-stats, i.e. instead of + returning an error when stat'ing a large file, the results will + be silently truncated unless perl itself is compiled with large + file support. + + Example: Print the length of /etc/passwd: + + aio_stat "/etc/passwd", sub { + $_[0] and die "stat failed: $!"; + print "size is ", -s _, "\n"; + }; + + aio_unlink $pathname, $callback->($status) + Asynchronously unlink (delete) a file and call the callback with + the result code. + + aio_link $srcpath, $dstpath, $callback->($status) + Asynchronously create a new link to the existing object at + $srcpath at the path $dstpath and call the callback with the + result code. + + aio_symlink $srcpath, $dstpath, $callback->($status) + Asynchronously create a new symbolic link to the existing object + at $srcpath at the path $dstpath and call the callback with the + result code. + + aio_rename $srcpath, $dstpath, $callback->($status) + Asynchronously rename the object at $srcpath to $dstpath, just + as rename(2) and call the callback with the result code. + + aio_rmdir $pathname, $callback->($status) + Asynchronously rmdir (delete) a directory and call the callback + with the result code. + + aio_readdir $pathname, $callback->($entries) + Unlike the POSIX call of the same name, "aio_readdir" reads an + entire directory (i.e. opendir + readdir + closedir). The + entries will not be sorted, and will NOT include the "." and + ".." entries. + + The callback a single argument which is either "undef" or an + array-ref with the filenames. + + aio_scandir $path, $maxreq, $callback->($dirs, $nondirs) + Scans a directory (similar to "aio_readdir") but additionally + tries to efficiently separate the entries of directory $path + into two sets of names, directories you can recurse into + (directories), and ones you cannot recurse into (everything + else, including symlinks to directories). + + "aio_scandir" is a composite request that creates of many sub + requests_ $maxreq specifies the maximum number of outstanding + aio requests that this function generates. If it is "<= 0", then + a suitable default will be chosen (currently 6). + + On error, the callback is called without arguments, otherwise it + receives two array-refs with path-relative entry names. + + Example: + + aio_scandir $dir, 0, sub { + my ($dirs, $nondirs) = @_; + print "real directories: @$dirs\n"; + print "everything else: @$nondirs\n"; + }; + + Implementation notes. + + The "aio_readdir" cannot be avoided, but "stat()"'ing every + entry can. + + After reading the directory, the modification time, size etc. of + the directory before and after the readdir is checked, and if + they match (and isn't the current time), the link count will be + used to decide how many entries are directories (if >= 2). + Otherwise, no knowledge of the number of subdirectories will be + assumed. + + Then entries will be sorted into likely directories (everything + without a non-initial dot currently) and likely non-directories + (everything else). Then every entry plus an appended "/." will + be "stat"'ed, likely directories first. If that succeeds, it + assumes that the entry is a directory or a symlink to directory + (which will be checked seperately). This is often faster than + stat'ing the entry itself because filesystems might detect the + type of the entry without reading the inode data (e.g. ext2fs + filetype feature). + + If the known number of directories (link count - 2) has been + reached, the rest of the entries is assumed to be + non-directories. + + This only works with certainty on POSIX (= UNIX) filesystems, + which fortunately are the vast majority of filesystems around. + + It will also likely work on non-POSIX filesystems with reduced + efficiency as those tend to return 0 or 1 as link counts, which + disables the directory counting heuristic. + + aio_fsync $fh, $callback->($status) + Asynchronously call fsync on the given filehandle and call the + callback with the fsync result code. + + aio_fdatasync $fh, $callback->($status) + Asynchronously call fdatasync on the given filehandle and call + the callback with the fdatasync result code. + + If this call isn't available because your OS lacks it or it + couldn't be detected, it will be emulated by calling "fsync" + instead. + + aio_group $callback->(...) + This is a very special aio request: Instead of doing something, + it is a container for other aio requests, which is useful if you + want to bundle many requests into a single, composite, request + with a definite callback and the ability to cancel the whole + request with its subrequests. + + Returns an object of class IO::AIO::GRP. See its documentation + below for more info. + + Example: + + my $grp = aio_group sub { + print "all stats done\n"; + }; + + add $grp + (aio_stat ...), + (aio_stat ...), + ...; + + aio_nop $callback->() + This is a special request - it does nothing in itself and is + only used for side effects, such as when you want to add a dummy + request to a group so that finishing the requests in the group + depends on executing the given code. + + While this request does nothing, it still goes through the + execution phase and still requires a worker thread. Thus, the + callback will not be executed immediately but only after other + requests in the queue have entered their execution phase. This + can be used to measure request latency. + + IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED* + Mainly used for debugging and benchmarking, this aio request + puts one of the request workers to sleep for the given time. + + While it is theoretically handy to have simple I/O scheduling + requests like sleep and file handle readable/writable, the + overhead this creates is immense (it blocks a thread for a long + time) so do not use this function except to put your application + under artificial I/O pressure. + + IO::AIO::REQ CLASS + All non-aggregate "aio_*" functions return an object of this class + when called in non-void context. + + cancel $req + Cancels the request, if possible. Has the effect of skipping + execution when entering the execute state and skipping calling + the callback when entering the the result state, but will leave + the request otherwise untouched. That means that requests that + currently execute will not be stopped and resources held by the + request will not be freed prematurely. + + cb $req $callback->(...) + Replace (or simply set) the callback registered to the request. + + IO::AIO::GRP CLASS + This class is a subclass of IO::AIO::REQ, so all its methods apply + to objects of this class, too. + + A IO::AIO::GRP object is a special request that can contain multiple + other aio requests. + + You create one by calling the "aio_group" constructing function with + a callback that will be called when all contained requests have + entered the "done" state: - aio_close $fh, $callback->($status) - Asynchronously close a file and call the callback with the result - code. *WARNING:* although accepted, you should not pass in a perl - filehandle here, as perl will likely close the file descriptor - another time when the filehandle is destroyed. Normally, you can - safely call perls "close" or just let filehandles go out of scope. - - This is supposed to be a bug in the API, so that might change. It's - therefore best to avoid this function. - - aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval) - aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval) - Reads or writes "length" bytes from the specified "fh" and "offset" - into the scalar given by "data" and offset "dataoffset" and calls - the callback without the actual number of bytes read (or -1 on - error, just like the syscall). - - The $data scalar *MUST NOT* be modified in any way while the request - is outstanding. Modifying it can result in segfaults or WW3 (if the - necessary/optional hardware is installed). - - Example: Read 15 bytes at offset 7 into scalar $buffer, starting at - offset 0 within the scalar: - - aio_read $fh, 7, 15, $buffer, 0, sub { - $_[0] > 0 or die "read error: $!"; - print "read $_[0] bytes: <$buffer>\n"; + my $grp = aio_group sub { + print "all requests are done\n"; }; - aio_move $srcpath, $dstpath, $callback->($status) - [EXPERIMENTAL] + You add requests by calling the "add" method with one or more + "IO::AIO::REQ" objects: - Try to move the *file* (directories not supported as either source - or destination) from $srcpath to $dstpath and call the callback with - the 0 (error) or -1 ok. - - This is a composite request that tries to rename(2) the file first. - If rename files with "EXDEV", it creates the destination file with - mode 0200 and copies the contents of the source file into it using - "aio_sendfile", followed by restoring atime, mtime, access mode and - uid/gid, in that order, and unlinking the $srcpath. - - If an error occurs, the partial destination file will be unlinked, - if possible, except when setting atime, mtime, access mode and - uid/gid, where errors are being ignored. - - aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval) - Tries to copy $length bytes from $in_fh to $out_fh. It starts - reading at byte offset $in_offset, and starts writing at the current - file offset of $out_fh. Because of that, it is not safe to issue - more than one "aio_sendfile" per $out_fh, as they will interfere - with each other. - - This call tries to make use of a native "sendfile" syscall to - provide zero-copy operation. For this to work, $out_fh should refer - to a socket, and $in_fh should refer to mmap'able file. - - If the native sendfile call fails or is not implemented, it will be - emulated, so you can call "aio_sendfile" on any type of filehandle - regardless of the limitations of the operating system. - - Please note, however, that "aio_sendfile" can read more bytes from - $in_fh than are written, and there is no way to find out how many - bytes have been read from "aio_sendfile" alone, as "aio_sendfile" - only provides the number of bytes written to $out_fh. Only if the - result value equals $length one can assume that $length bytes have - been read. - - aio_readahead $fh,$offset,$length, $callback->($retval) - "aio_readahead" populates the page cache with data from a file so - that subsequent reads from that file will not block on disk I/O. The - $offset argument specifies the starting point from which data is to - be read and $length specifies the number of bytes to be read. I/O is - performed in whole pages, so that offset is effectively rounded down - to a page boundary and bytes are read up to the next page boundary - greater than or equal to (off-set+length). "aio_readahead" does not - read beyond the end of the file. The current file offset of the file - is left unchanged. - - If that syscall doesn't exist (likely if your OS isn't Linux) it - will be emulated by simply reading the data, which would have a - similar effect. - - aio_stat $fh_or_path, $callback->($status) - aio_lstat $fh, $callback->($status) - Works like perl's "stat" or "lstat" in void context. The callback - will be called after the stat and the results will be available - using "stat _" or "-s _" etc... - - The pathname passed to "aio_stat" must be absolute. See API NOTES, - above, for an explanation. - - Currently, the stats are always 64-bit-stats, i.e. instead of - returning an error when stat'ing a large file, the results will be - silently truncated unless perl itself is compiled with large file - support. - - Example: Print the length of /etc/passwd: - - aio_stat "/etc/passwd", sub { - $_[0] and die "stat failed: $!"; - print "size is ", -s _, "\n"; - }; + $grp->add (aio_unlink "..."); - aio_unlink $pathname, $callback->($status) - Asynchronously unlink (delete) a file and call the callback with the - result code. - - aio_link $srcpath, $dstpath, $callback->($status) - Asynchronously create a new link to the existing object at $srcpath - at the path $dstpath and call the callback with the result code. - - aio_symlink $srcpath, $dstpath, $callback->($status) - Asynchronously create a new symbolic link to the existing object at - $srcpath at the path $dstpath and call the callback with the result - code. - - aio_rename $srcpath, $dstpath, $callback->($status) - Asynchronously rename the object at $srcpath to $dstpath, just as - rename(2) and call the callback with the result code. - - aio_rmdir $pathname, $callback->($status) - Asynchronously rmdir (delete) a directory and call the callback with - the result code. - - aio_readdir $pathname, $callback->($entries) - Unlike the POSIX call of the same name, "aio_readdir" reads an - entire directory (i.e. opendir + readdir + closedir). The entries - will not be sorted, and will NOT include the "." and ".." entries. - - The callback a single argument which is either "undef" or an - array-ref with the filenames. - - aio_scandir $path, $maxreq, $callback->($dirs, $nondirs) - Scans a directory (similar to "aio_readdir") and tries to separate - the entries of directory $path into two sets of names, ones you can - recurse into (directories), and ones you cannot recurse into - (everything else). - - "aio_scandir" is a composite request that consists of many - aio-primitives. $maxreq specifies the maximum number of outstanding - aio requests that this function generates. If it is "<= 0", then a - suitable default will be chosen (currently 8). - - On error, the callback is called without arguments, otherwise it - receives two array-refs with path-relative entry names. - - Example: - - aio_scandir $dir, 0, sub { - my ($dirs, $nondirs) = @_; - print "real directories: @$dirs\n"; - print "everything else: @$nondirs\n"; - }; + add $grp aio_stat "...", sub { + $_[0] or return $grp->result ("error"); - Implementation notes. + # add another request dynamically, if first succeeded + add $grp aio_open "...", sub { + $grp->result ("ok"); + }; + }; - The "aio_readdir" cannot be avoided, but "stat()"'ing every entry - can. + This makes it very easy to create composite requests (see the source + of "aio_move" for an application) that work and feel like simple + requests. - After reading the directory, the modification time, size etc. of the - directory before and after the readdir is checked, and if they - match, the link count will be used to decide how many entries are - directories (if >= 2). Otherwise, no knowledge of the number of - subdirectories will be assumed. - - Then entires will be sorted into likely directories (everything - without a non-initial dot) and likely non-directories (everything - else). Then every entry + "/." will be "stat"'ed, likely directories - first. This is often faster because filesystems might detect the - type of the entry without reading the inode data (e.g. ext2fs - filetype feature). If that succeeds, it assumes that the entry is a - directory or a symlink to directory (which will be checked - seperately). - - If the known number of directories has been reached, the rest of the - entries is assumed to be non-directories. - - aio_fsync $fh, $callback->($status) - Asynchronously call fsync on the given filehandle and call the - callback with the fsync result code. - - aio_fdatasync $fh, $callback->($status) - Asynchronously call fdatasync on the given filehandle and call the - callback with the fdatasync result code. + * The IO::AIO::GRP objects will be cleaned up during calls to + "IO::AIO::poll_cb", just like any other request. + * They can be canceled like any other request. Canceling will cancel + not only the request itself, but also all requests it contains. + * They can also can also be added to other IO::AIO::GRP objects. + * You must not add requests to a group from within the group + callback (or any later time). + + Their lifetime, simplified, looks like this: when they are empty, + they will finish very quickly. If they contain only requests that + are in the "done" state, they will also finish. Otherwise they will + continue to exist. + + That means after creating a group you have some time to add + requests. And in the callbacks of those requests, you can add + further requests to the group. And only when all those requests have + finished will the the group itself finish. + + add $grp ... + $grp->add (...) + Add one or more requests to the group. Any type of IO::AIO::REQ + can be added, including other groups, as long as you do not + create circular dependencies. + + Returns all its arguments. + + $grp->cancel_subs + Cancel all subrequests and clears any feeder, but not the group + request itself. Useful when you queued a lot of events but got a + result early. + + $grp->result (...) + Set the result value(s) that will be passed to the group + callback when all subrequests have finished and set thre groups + errno to the current value of errno (just like calling "errno" + without an error number). By default, no argument will be passed + and errno is zero. + + $grp->errno ([$errno]) + Sets the group errno value to $errno, or the current value of + errno when the argument is missing. + + Every aio request has an associated errno value that is restored + when the callback is invoked. This method lets you change this + value from its default (0). + + Calling "result" will also set errno, so make sure you either + set $! before the call to "result", or call c after it. + + feed $grp $callback->($grp) + Sets a feeder/generator on this group: every group can have an + attached generator that generates requests if idle. The idea + behind this is that, although you could just queue as many + requests as you want in a group, this might starve other + requests for a potentially long time. For example, "aio_scandir" + might generate hundreds of thousands "aio_stat" requests, + delaying any later requests for a long time. + + To avoid this, and allow incremental generation of requests, you + can instead a group and set a feeder on it that generates those + requests. The feed callback will be called whenever there are + few enough (see "limit", below) requests active in the group + itself and is expected to queue more requests. + + The feed callback can queue as many requests as it likes (i.e. + "add" does not impose any limits). + + If the feed does not queue more requests when called, it will be + automatically removed from the group. + + If the feed limit is 0, it will be set to 2 automatically. + + Example: + + # stat all files in @files, but only ever use four aio requests concurrently: + + my $grp = aio_group sub { print "finished\n" }; + limit $grp 4; + feed $grp sub { + my $file = pop @files + or return; + + add $grp aio_stat $file, sub { ... }; + }; + + limit $grp $num + Sets the feeder limit for the group: The feeder will be called + whenever the group contains less than this many requests. - If this call isn't available because your OS lacks it or it couldn't - be detected, it will be emulated by calling "fsync" instead. + Setting the limit to 0 will pause the feeding process. SUPPORT FUNCTIONS - $fileno = IO::AIO::poll_fileno - Return the *request result pipe file descriptor*. This filehandle - must be polled for reading by some mechanism outside this module - (e.g. Event or select, see below or the SYNOPSIS). If the pipe - becomes readable you have to call "poll_cb" to check the results. + $fileno = IO::AIO::poll_fileno + Return the *request result pipe file descriptor*. This + filehandle must be polled for reading by some mechanism outside + this module (e.g. Event or select, see below or the SYNOPSIS). + If the pipe becomes readable you have to call "poll_cb" to check + the results. - See "poll_cb" for an example. + See "poll_cb" for an example. - IO::AIO::poll_cb - Process all outstanding events on the result pipe. You have to call - this regularly. Returns the number of events processed. Returns - immediately when no events are outstanding. + IO::AIO::poll_cb + Process all outstanding events on the result pipe. You have to + call this regularly. Returns the number of events processed. + Returns immediately when no events are outstanding. - Example: Install an Event watcher that automatically calls - IO::AIO::poll_cb with high priority: + If not all requests were processed for whatever reason, the + filehandle will still be ready when "poll_cb" returns. - Event->io (fd => IO::AIO::poll_fileno, - poll => 'r', async => 1, - cb => \&IO::AIO::poll_cb); + Example: Install an Event watcher that automatically calls + IO::AIO::poll_cb with high priority: - IO::AIO::poll_wait - Wait till the result filehandle becomes ready for reading (simply - does a "select" on the filehandle. This is useful if you want to - synchronously wait for some requests to finish). + Event->io (fd => IO::AIO::poll_fileno, + poll => 'r', async => 1, + cb => \&IO::AIO::poll_cb); - See "nreqs" for an example. + IO::AIO::poll_some $max_requests + Similar to "poll_cb", but only processes up to $max_requests + requests at a time. - IO::AIO::nreqs - Returns the number of requests currently outstanding (i.e. for which - their callback has not been invoked yet). + Useful if you want to ensure some level of interactiveness when + perl is not fast enough to process all requests in time. - Example: wait till there are no outstanding requests anymore: + Example: Install an Event watcher that automatically calls + IO::AIO::poll_some with low priority, to ensure that other parts + of the program get the CPU sometimes even under high AIO load. - IO::AIO::poll_wait, IO::AIO::poll_cb - while IO::AIO::nreqs; + Event->io (fd => IO::AIO::poll_fileno, + poll => 'r', nice => 1, + cb => sub { IO::AIO::poll_some 256 }); - IO::AIO::flush - Wait till all outstanding AIO requests have been handled. + IO::AIO::poll_wait + Wait till the result filehandle becomes ready for reading + (simply does a "select" on the filehandle. This is useful if you + want to synchronously wait for some requests to finish). - Strictly equivalent to: + See "nreqs" for an example. - IO::AIO::poll_wait, IO::AIO::poll_cb - while IO::AIO::nreqs; + IO::AIO::nreqs + Returns the number of requests currently in the ready, execute + or pending states (i.e. for which their callback has not been + invoked yet). - IO::AIO::poll - Waits until some requests have been handled. + Example: wait till there are no outstanding requests anymore: - Strictly equivalent to: + IO::AIO::poll_wait, IO::AIO::poll_cb + while IO::AIO::nreqs; - IO::AIO::poll_wait, IO::AIO::poll_cb - if IO::AIO::nreqs; + IO::AIO::nready + Returns the number of requests currently in the ready state (not + yet executed). - IO::AIO::min_parallel $nthreads - Set the minimum number of AIO threads to $nthreads. The current - default is 4, which means four asynchronous operations can be done - at one time (the number of outstanding operations, however, is - unlimited). + IO::AIO::npending + Returns the number of requests currently in the pending state + (executed, but not yet processed by poll_cb). - IO::AIO starts threads only on demand, when an AIO request is queued - and no free thread exists. + IO::AIO::flush + Wait till all outstanding AIO requests have been handled. - It is recommended to keep the number of threads low, as some Linux - kernel versions will scale negatively with the number of threads - (higher parallelity => MUCH higher latency). With current Linux 2.6 - versions, 4-32 threads should be fine. + Strictly equivalent to: - Under most circumstances you don't need to call this function, as - the module selects a default that is suitable for low to moderate - load. + IO::AIO::poll_wait, IO::AIO::poll_cb + while IO::AIO::nreqs; - IO::AIO::max_parallel $nthreads - Sets the maximum number of AIO threads to $nthreads. If more than - the specified number of threads are currently running, this function - kills them. This function blocks until the limit is reached. + IO::AIO::poll + Waits until some requests have been handled. - While $nthreads are zero, aio requests get queued but not executed - until the number of threads has been increased again. + Strictly equivalent to: - This module automatically runs "max_parallel 0" at program end, to - ensure that all threads are killed and that there are no outstanding - requests. + IO::AIO::poll_wait, IO::AIO::poll_cb + if IO::AIO::nreqs; + + IO::AIO::min_parallel $nthreads + Set the minimum number of AIO threads to $nthreads. The current + default is 8, which means eight asynchronous operations can + execute concurrently at any one time (the number of outstanding + requests, however, is unlimited). - Under normal circumstances you don't need to call this function. + IO::AIO starts threads only on demand, when an AIO request is + queued and no free thread exists. - $oldnreqs = IO::AIO::max_outstanding $nreqs - Sets the maximum number of outstanding requests to $nreqs. If you - try to queue up more than this number of requests, the caller will - block until some requests have been handled. - - The default is very large, so normally there is no practical limit. - If you queue up many requests in a loop it often improves speed if - you set this to a relatively low number, such as 100. + It is recommended to keep the number of threads relatively low, + as some Linux kernel versions will scale negatively with the + number of threads (higher parallelity => MUCH higher latency). + With current Linux 2.6 versions, 4-32 threads should be fine. - Under normal circumstances you don't need to call this function. + Under most circumstances you don't need to call this function, + as the module selects a default that is suitable for low to + moderate load. + + IO::AIO::max_parallel $nthreads + Sets the maximum number of AIO threads to $nthreads. If more + than the specified number of threads are currently running, this + function kills them. This function blocks until the limit is + reached. + + While $nthreads are zero, aio requests get queued but not + executed until the number of threads has been increased again. + + This module automatically runs "max_parallel 0" at program end, + to ensure that all threads are killed and that there are no + outstanding requests. + + Under normal circumstances you don't need to call this function. + + $oldmaxreqs = IO::AIO::max_outstanding $maxreqs + This is a very bad function to use in interactive programs + because it blocks, and a bad way to reduce concurrency because + it is inexact: Better use an "aio_group" together with a feed + callback. + + Sets the maximum number of outstanding requests to $nreqs. If + you to queue up more than this number of requests, the next call + to the "poll_cb" (and "poll_some" and other functions calling + "poll_cb") function will block until the limit is no longer + exceeded. + + The default value is very large, so there is no practical limit + on the number of outstanding requests. + + You can still queue as many requests as you want. Therefore, + "max_oustsanding" is mainly useful in simple scripts (with low + values) or as a stop gap to shield against fatal memory overflow + (with large values). FORK BEHAVIOUR - Before the fork, IO::AIO enters a quiescent state where no requests can - be added in other threads and no results will be processed. After the - fork the parent simply leaves the quiescent state and continues - request/result processing, while the child clears the request/result - queue (so the requests started before the fork will only be handled in - the parent). Threats will be started on demand until the limit ste in - the parent process has been reached again. + This module should do "the right thing" when the process using it + forks: + + Before the fork, IO::AIO enters a quiescent state where no requests + can be added in other threads and no results will be processed. + After the fork the parent simply leaves the quiescent state and + continues request/result processing, while the child frees the + request/result queue (so that the requests started before the fork + will only be handled in the parent). Threads will be started on + demand until the limit set in the parent process has been reached + again. + + In short: the parent will, after a short pause, continue as if fork + had not been called, while the child will act as if IO::AIO has not + been used yet. + + MEMORY USAGE + Per-request usage: + + Each aio request uses - depending on your architecture - around + 100-200 bytes of memory. In addition, stat requests need a stat + buffer (possibly a few hundred bytes), readdir requires a result + buffer and so on. Perl scalars and other data passed into aio + requests will also be locked and will consume memory till the + request has entered the done state. + + This is now awfully much, so queuing lots of requests is not usually + a problem. + + Per-thread usage: + + In the execution phase, some aio requests require more memory for + temporary buffers, and each thread requires a stack and other data + structures (usually around 16k-128k, depending on the OS). + +KNOWN BUGS + Known bugs will be fixed in the next release. SEE ALSO - Coro, Linux::AIO. + Coro::AIO. AUTHOR - Marc Lehmann - http://home.schmorp.de/ + Marc Lehmann + http://home.schmorp.de/