U:RDoc::AnyMethod[iI"select:ETI"Kernel#select;TF:publico:RDoc::Markup::Document:@parts[-o:RDoc::Markup::Paragraph; [I""Calls select(2) system call. ;TI"RIt monitors given arrays of IO objects, waits until one or more ;TI"Nof IO objects are ready for reading, are ready for writing, ;TI"Iand have pending exceptions respectively, and returns an array that ;TI"@contains arrays of those IO objects. It will return +nil+ ;TI"Mif optional timeout value is given and no IO object ;TI"(is ready in timeout seconds.;To:RDoc::Markup::BlankLineo; ; [ I"aIO.select peeks the buffer of IO objects for testing readability. ;TI"1If the IO buffer is not empty, ;TI">IO.select immediately notifies readability. ;TI";This "peek" only happens for IO objects. ;TI"LIt does not happen for IO-like objects such as OpenSSL::SSL::SSLSocket.;T@o; ; [I"?The best way to use IO.select is invoking it ;TI"eafter nonblocking methods such as read_nonblock, write_nonblock, etc. ;TI"9The methods raise an exception which is extended by ;TI"EIO::WaitReadable or IO::WaitWritable. ;TI"PThe modules notify how the caller should wait with IO.select. ;TI"UIf IO::WaitReadable is raised, the caller should wait for reading. ;TI"TIf IO::WaitWritable is raised, the caller should wait for writing.;T@o; ; [I"HSo, blocking read (readpartial) can be emulated using ;TI"Fread_nonblock and IO.select as follows:;T@o:RDoc::Markup::Verbatim; [I"begin ;TI". result = io_like.read_nonblock(maxlen) ;TI"rescue IO::WaitReadable ;TI" IO.select([io_like]) ;TI" retry ;TI"rescue IO::WaitWritable ;TI"! IO.select(nil, [io_like]) ;TI" retry ;TI" end ;T:@format0o; ; [ I"IO.select is preferred for IO like ;TI";objects such as OpenSSL::SSL::SSLSocket. ;TI"SIt has to_io method to return underlying IO object. ;TI"[IO.select calls to_io to obtain the file descriptor to wait.;T@o; ; [I"QThis means that readability notified by IO.select doesn't mean ;TI"Breadability from OpenSSL::SSL::SSLSocket object.;T@o; ; [I"_The most likely situation is that OpenSSL::SSL::SSLSocket buffers some data. ;TI"4IO.select doesn't see the buffer. ;TI"mSo IO.select can block when OpenSSL::SSL::SSLSocket#readpartial doesn't block.;T@o; ; [I"8However, several more complicated situations exist.;T@o; ; [I"5SSL is a protocol which is sequence of records. ;TI",The record consists of multiple bytes. ;TI"8So, the remote side of SSL sends a partial record, ;TI"5IO.select notifies readability but ;TI"DOpenSSL::SSL::SSLSocket cannot decrypt a byte and ;TI"BOpenSSL::SSL::SSLSocket#readpartial will blocks.;T@o; ; [I"FAlso, the remote side can request SSL renegotiation which forces ;TI".the local SSL engine to write some data. ;TI"EThis means OpenSSL::SSL::SSLSocket#readpartial may ;TI"=invoke write system call and it can block. ;TI"MIn such a situation, OpenSSL::SSL::SSLSocket#read_nonblock ;TI"2raises IO::WaitWritable instead of blocking. ;TI"KSo, the caller should wait for ready for writability as above example.;T@o; ; [I"JThe combination of nonblocking methods and IO.select is ;TI"Balso useful for streams such as tty, pipe socket socket when ;TI"+multiple processes read from a stream.;T@o; ; [ I";Finally, Linux kernel developers don't guarantee that ;TI"Jreadability of select(2) means readability of following read(2) even ;TI"for a single process. ;TI".See select(2) manual on GNU/Linux system.;T@o; ; [I"]Invoking IO.select before IO#readpartial works well as usual. ;TI"BHowever it is not the best way to use IO.select.;T@o; ; [ I"8The writability notified by select(2) doesn't show ;TI"how many bytes writable. ;TI"NIO#write method blocks until given whole string is written. ;TI"uSo, IO#write(two or more bytes) can block after writability is notified by IO.select. ;TI"FIO#write_nonblock is required to avoid the blocking.;T@o; ; [I"?Blocking write (write) can be emulated using ;TI"Hwrite_nonblock and IO.select as follows: ;TI"kIO::WaitReadable should also be rescued for SSL renegotiation in OpenSSL::SSL::SSLSocket.;T@o;; [I"while 0 < string.bytesize ;TI" begin ;TI"2 written = io_like.write_nonblock(string) ;TI" rescue IO::WaitReadable ;TI" IO.select([io_like]) ;TI" retry ;TI" rescue IO::WaitWritable ;TI"# IO.select(nil, [io_like]) ;TI" retry ;TI" end ;TI". string = string.byteslice(written..-1) ;TI" end ;T; 0S:RDoc::Markup::Heading: leveli: textI"Parameters;To:RDoc::Markup::List: @type: NOTE:@items[ o:RDoc::Markup::ListItem:@label[I"read_array;T; [o; ; [I"Gan array of IO objects that wait until ready for read;To;;[I"write_array;T; [o; ; [I"Han array of IO objects that wait until ready for write;To;;[I"error_array;T; [o; ; [I"Aan array of IO objects that wait for exceptions;To;;[I"timeout;T; [o; ; [I"a numeric value in second;T@S;;i;I"Example;T@o;; [I"rp, wp = IO.pipe ;TI"mesg = "ping " ;TI"100.times { ;TI"H # IO.select follows IO#read. Not the best way to use IO.select. ;TI"' rs, ws, = IO.select([rp], [wp]) ;TI" if r = rs[0] ;TI" ret = r.read(5) ;TI" print ret ;TI" case ret ;TI" when /ping/ ;TI" mesg = "pong\n" ;TI" when /pong/ ;TI" mesg = "ping " ;TI" end ;TI" end ;TI" if w = ws[0] ;TI" w.write(mesg) ;TI" end ;TI"} ;T; 0o; ; [I"produces:;T@o;; [ I"ping pong ;TI"ping pong ;TI"ping pong ;TI"(snipped) ;TI" ping;T; 0: @fileI" io.c;T:0@omit_headings_from_table_of_contents_below0I"WIO.select(read_array [, write_array [, error_array [, timeout]]]) -> array or nil ;T0[I"$(p1, p2 = v2, p3 = v3, p4 = v4);T@�FI"Kernel;TcRDoc::NormalModule00