Invokes system call select(2), which monitors multiple file descriptors, waiting until one or more of the file descriptors becomes ready for some class of I/O operation.
Not implemented on all platforms.
Each of the arguments read_ios, write_ios, and error_ios is an array of IO objects.
Argument timeout is an integer timeout interval in seconds.
The method monitors the IO objects given in all three arrays, waiting for some to be ready; returns a 3-element array whose elements are:
An array of the objects in read_ios that are ready for reading.
An array of the objects in write_ios that are ready for writing.
An array of the objects in error_ios have pending exceptions.
If no object becomes ready within the given timeout, nil is returned.
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 non-blocking 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 non-blocking 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 block.
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 non-blocking 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)
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 are 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
Example:
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 }
Output:
ping pong ping pong ping pong (snipped) ping
Returns the Encoding object that represents the encoding of obj.
Replaces the elements with ones returned by collect(). Returns an enumerator if no block is given.
Equivalent to Set#keep_if, but returns nil if no changes were made. Returns an enumerator if no block is given.
With a block given, returns an array of values from self for which the block returns a truthy value:
Customer = Struct.new(:name, :address, :zip) joe = Customer.new("Joe Smith", "123 Maple, Anytown NC", 12345) a = joe.select {|value| value.is_a?(String) } a # => ["Joe Smith", "123 Maple, Anytown NC"] a = joe.select {|value| value.is_a?(Integer) } a # => [12345]
With no block given, returns an Enumerator.
Equivalent to self.to_s.encoding; see String#encoding.
Returns true if self points to a mountpoint.
Returns a new Hash object whose entries are those for which the block returns a truthy value:
h = {foo: 0, bar: 1, baz: 2} h.select {|key, value| value < 2 } # => {:foo=>0, :bar=>1}
Returns a new Enumerator if no block given:
h = {foo: 0, bar: 1, baz: 2} e = h.select # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:select> e.each {|key, value| value < 2 } # => {:foo=>0, :bar=>1}
Returns self, whose entries are those for which the block returns a truthy value:
h = {foo: 0, bar: 1, baz: 2}
h.select! {|key, value| value < 2 } => {:foo=>0, :bar=>1}
Returns nil if no entries were removed.
Returns a new Enumerator if no block given:
h = {foo: 0, bar: 1, baz: 2} e = h.select! # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:select!> e.each { |key, value| value < 2 } # => {:foo=>0, :bar=>1}
Yields each environment variable name and its value as a 2-element Array, returning a Hash of the names and values for which the block returns a truthy value:
ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2') ENV.select { |name, value| name.start_with?('b') } # => {"bar"=>"1", "baz"=>"2"} ENV.filter { |name, value| name.start_with?('b') } # => {"bar"=>"1", "baz"=>"2"}
Returns an Enumerator if no block given:
e = ENV.select # => #<Enumerator: {"bar"=>"1", "baz"=>"2", "foo"=>"0"}:select> e.each { |name, value | name.start_with?('b') } # => {"bar"=>"1", "baz"=>"2"} e = ENV.filter # => #<Enumerator: {"bar"=>"1", "baz"=>"2", "foo"=>"0"}:filter> e.each { |name, value | name.start_with?('b') } # => {"bar"=>"1", "baz"=>"2"}
Yields each environment variable name and its value as a 2-element Array, deleting each entry for which the block returns false or nil, and returning ENV if any deletions made, or nil otherwise:
ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2') ENV.select! { |name, value| name.start_with?('b') } # => ENV ENV # => {"bar"=>"1", "baz"=>"2"} ENV.select! { |name, value| true } # => nil ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2') ENV.filter! { |name, value| name.start_with?('b') } # => ENV ENV # => {"bar"=>"1", "baz"=>"2"} ENV.filter! { |name, value| true } # => nil
Returns an Enumerator if no block given:
ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2') e = ENV.select! # => #<Enumerator: {"bar"=>"1", "baz"=>"2"}:select!> e.each { |name, value| name.start_with?('b') } # => ENV ENV # => {"bar"=>"1", "baz"=>"2"} e.each { |name, value| true } # => nil ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2') e = ENV.filter! # => #<Enumerator: {"bar"=>"1", "baz"=>"2"}:filter!> e.each { |name, value| name.start_with?('b') } # => ENV ENV # => {"bar"=>"1", "baz"=>"2"} e.each { |name, value| true } # => nil
Wait for any ractor to have something in its outgoing port, read from this ractor, and then return that ractor and the object received.
r1 = Ractor.new {Ractor.yield 'from 1'} r2 = Ractor.new {Ractor.yield 'from 2'} r, obj = Ractor.select(r1, r2) puts "received #{obj.inspect} from #{r.inspect}" # Prints: received "from 1" from #<Ractor:#2 test.rb:1 running> # But could just as well print "from r2" here, either prints could be first.
If one of the given ractors is the current ractor, and it is selected, r will contain the :receive symbol instead of the ractor object.
r1 = Ractor.new(Ractor.current) do |main| main.send 'to main' Ractor.yield 'from 1' end r2 = Ractor.new do Ractor.yield 'from 2' end r, obj = Ractor.select(r1, r2, Ractor.current) puts "received #{obj.inspect} from #{r.inspect}" # Could print: received "to main" from :receive
If yield_value is provided, that value may be yielded if another ractor is calling take. In this case, the pair [:yield, nil] is returned:
r1 = Ractor.new(Ractor.current) do |main| puts "Received from main: #{main.take}" end puts "Trying to select" r, obj = Ractor.select(r1, Ractor.current, yield_value: 123) wait puts "Received #{obj.inspect} from #{r.inspect}"
This will print:
Trying to select Received from main: 123 Received nil from :yield
move boolean flag defines whether yielded value will be copied (default) or moved.
Invokes system call select(2), which monitors multiple file descriptors, waiting until one or more of the file descriptors becomes ready for some class of I/O operation.
Not implemented on all platforms.
Each of the arguments read_ios, write_ios, and error_ios is an array of IO objects.
Argument timeout is an integer timeout interval in seconds.
The method monitors the IO objects given in all three arrays, waiting for some to be ready; returns a 3-element array whose elements are:
An array of the objects in read_ios that are ready for reading.
An array of the objects in write_ios that are ready for writing.
An array of the objects in error_ios have pending exceptions.
If no object becomes ready within the given timeout, nil is returned.
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 non-blocking 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 non-blocking 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 block.
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 non-blocking 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)
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 are 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
Example:
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 }
Output:
ping pong ping pong ping pong (snipped) ping
Returns an array containing elements selected by the block.
With a block given, calls the block with successive elements; returns an array of those elements for which the block returns a truthy value:
(0..9).select {|element| element % 3 == 0 } # => [0, 3, 6, 9] a = {foo: 0, bar: 1, baz: 2}.select {|key, value| key.start_with?('b') } a # => {:bar=>1, :baz=>2}
With no block given, returns an Enumerator.
Related: reject.
Returns an array of objects returned by the block.
With a block given, calls the block with successive elements; returns an array of the objects returned by the block:
(0..4).map {|i| i*i } # => [0, 1, 4, 9, 16] {foo: 0, bar: 1, baz: 2}.map {|key, value| value*2} # => [0, 2, 4]
With no block given, returns an Enumerator.
Generates a hex-encoded version of a given string.
Returns a string containing the RFC-2045-compliant Base64-encoding of bin.
Per RFC 2045, the returned string may contain the URL-unsafe characters + or /; see Encoding Character Set above:
Base64.encode64("\xFB\xEF\xBE") # => "++++\n" Base64.encode64("\xFF\xFF\xFF") # => "////\n"
The returned string may include padding; see Padding above.
Base64.encode64('*') # => "Kg==\n"
The returned string ends with a newline character, and if sufficiently long will have one or more embedded newline characters; see Newlines above:
Base64.encode64('*') # => "Kg==\n" Base64.encode64('*' * 46) # => "KioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioq\nKg==\n"
The string to be encoded may itself contain newlines, which will be encoded as ordinary Base64:
Base64.encode64("\n\n\n") # => "CgoK\n" s = "This is line 1\nThis is line 2\n" Base64.encode64(s) # => "VGhpcyBpcyBsaW5lIDEKVGhpcyBpcyBsaW5lIDIK\n"
Detaches the current process from its controlling terminal and runs it in the background as system daemon; returns zero.
By default:
Changes the current working directory to the root directory.
Redirects $stdin, $stdout, and $stderr to the null device.
If optional argument nochdir is true, does not change the current working directory.
If optional argument noclose is true, does not redirect $stdin, $stdout, or $stderr.
Clear recorded tracing information.
Takes a token and gets the next token in the Negotiate authentication chain. Token can be Base64 encoded or not. The token can include the “Negotiate” header and it will be stripped. Does not indicate if SEC_I_CONTINUE or SEC_E_OK was returned. Token returned is Base64 encoded w/ all new lines removed.