Returns true if the date is Monday.
Returns the month of the year (1..12) for time.
t = Time.now #=> 2007-11-19 08:27:30 -0600 t.mon #=> 11 t.month #=> 11
Returns the month of the year (1..12) for time.
t = Time.now #=> 2007-11-19 08:27:30 -0600 t.mon #=> 11 t.month #=> 11
Returns true if time represents Monday.
t = Time.local(2003, 8, 4) #=> 2003-08-04 00:00:00 -0500 p t.monday? #=> true
Returns a new array consisting of the [key, value] pairs for which the code block returns true.
Yields each member value from the struct to the block and returns an Array containing the member values from the struct for which the given block returns a true value (equivalent to Enumerable#select).
Lots = Struct.new(:a, :b, :c, :d, :e, :f) l = Lots.new(11, 22, 33, 44, 55, 66) l.select {|v| (v % 2).zero? } #=> [22, 44, 66]
Returns an File instance opened console.
If sym is given, it will be sent to the opened console with args and the result will be returned instead of the console IO itself.
You must require ‘io/console’ to use this method.
Calls select(2) system call. It monitors given arrays of IO objects, waits until one or more of IO objects are ready for reading, are ready for writing, and have pending exceptions respectively, and returns an array that contains arrays of those IO objects. It will return nil if optional timeout value is given and no IO object is ready in timeout seconds.
IO.select peeks the buffer of IO objects for testing readability. If the IO buffer is not empty, IO.select immediately notifies readability. This “peek” only happens for IO objects. It does not happen for IO-like objects such as OpenSSL::SSL::SSLSocket.
The best way to use IO.select is invoking it after nonblocking methods such as read_nonblock, write_nonblock, etc. The methods raise an exception which is extended by IO::WaitReadable or IO::WaitWritable. The modules notify how the caller should wait with IO.select. If IO::WaitReadable is raised, the caller should wait for reading. If IO::WaitWritable is raised, the caller should wait for writing.
So, blocking read (readpartial) can be emulated using read_nonblock and IO.select as follows:
begin result = io_like.read_nonblock(maxlen) rescue IO::WaitReadable IO.select([io_like]) retry rescue IO::WaitWritable IO.select(nil, [io_like]) retry end
Especially, the combination of nonblocking methods and IO.select is preferred for IO like objects such as OpenSSL::SSL::SSLSocket. It has to_io method to return underlying IO object. IO.select calls to_io to obtain the file descriptor to wait.
This means that readability notified by IO.select doesn’t mean readability from OpenSSL::SSL::SSLSocket object.
The most likely situation is that OpenSSL::SSL::SSLSocket buffers some data. IO.select doesn’t see the buffer. So IO.select can block when OpenSSL::SSL::SSLSocket#readpartial doesn’t block.
However, several more complicated situations exist.
SSL is a protocol which is sequence of records. The record consists of multiple bytes. So, the remote side of SSL sends a partial record, IO.select notifies readability but OpenSSL::SSL::SSLSocket cannot decrypt a byte and OpenSSL::SSL::SSLSocket#readpartial will blocks.
Also, the remote side can request SSL renegotiation which forces the local SSL engine to write some data. This means OpenSSL::SSL::SSLSocket#readpartial may invoke write system call and it can block. In such a situation, OpenSSL::SSL::SSLSocket#read_nonblock raises IO::WaitWritable instead of blocking. So, the caller should wait for ready for writability as above example.
The combination of nonblocking methods and IO.select is also useful for streams such as tty, pipe socket socket when multiple processes read from a stream.
Finally, Linux kernel developers don’t guarantee that readability of select(2) means readability of following read(2) even for a single process. See select(2) manual on GNU/Linux system.
Invoking IO.select before IO#readpartial works well as usual. However it is not the best way to use IO.select.
The writability notified by select(2) doesn’t show how many bytes writable. IO#write method blocks until given whole string is written. So, IO#write(two or more bytes) can block after writability is notified by IO.select. IO#write_nonblock is required to avoid the blocking.
Blocking write (write) can be emulated using write_nonblock and IO.select as follows: IO::WaitReadable should also be rescued for SSL renegotiation in OpenSSL::SSL::SSLSocket.
while 0 < string.bytesize begin written = io_like.write_nonblock(string) rescue IO::WaitReadable IO.select([io_like]) retry rescue IO::WaitWritable IO.select(nil, [io_like]) retry end string = string.byteslice(written..-1) end
an array of IO objects that wait until ready for read
an array of IO objects that wait until ready for write
an array of IO objects that wait for exceptions
a numeric value in second
rp, wp = IO.pipe mesg = "ping " 100.times { # IO.select follows IO#read. Not the best way to use IO.select. rs, ws, = IO.select([rp], [wp]) if r = rs[0] ret = r.read(5) print ret case ret when /ping/ mesg = "pong\n" when /pong/ mesg = "ping " end end if w = ws[0] w.write(mesg) end }
produces:
ping pong ping pong ping pong (snipped) ping
Returns a new array of all key-value pairs of the database for which block evaluates to true.
Returns the Encoding object that represents the encoding of obj.
Returns the Encoding object that represents the encoding of sym.
Returns true if self points to a mountpoint.
Return encoding of the source.
Returns a new Array of key-value pairs for which the block returns true.
Example:
require 'sdbm' SDBM.open 'my_database' do |db| db['apple'] = 'fruit' db['pear'] = 'fruit' db['spinach'] = 'vegetable' veggies = db.select do |key, value| value == 'vegetable' end #=> [["apple", "fruit"], ["pear", "fruit"]] end
Returns a new hash consisting of entries for which the block returns true.
If no block is given, an enumerator is returned instead.
h = { "a" => 100, "b" => 200, "c" => 300 } h.select {|k,v| k > "a"} #=> {"b" => 200, "c" => 300} h.select {|k,v| v < 200} #=> {"a" => 100}
Equivalent to Hash#keep_if, but returns nil if no changes were made.
Returns a copy of the environment for entries where the block returns true.
Returns an Enumerator if no block was given.
Equivalent to ENV#keep_if but returns nil if no changes were made.
Returns a matrix that is the result of iteration of the given block over all elements of the matrix.
Matrix[ [1,2], [3,4] ].collect { |e| e**2 }
=> 1 4
9 16
Collects (as in Enumerable#collect) over the elements of this vector and v in conjunction.
Like Array#collect.
Replaces the elements with ones returned by collect().