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parallel_io.rb
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parallel_io.rb
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class Rubysh::Subprocess
class ParallelIO
module EOF; end
class NothingAvailable < StandardError; end
# readers/writers should be hashes mapping {fd => name}
def initialize(readers, writers)
@finished_readers = Set.new
@on_read = nil
@readers = readers
@writers = writers
@finished_writers = Set.new
@on_write = nil
@writer_buffers = {}
end
def register_reader(reader, name)
@readers[reader] = name
end
def register_writer(writer, name)
@writers[writer] = name
end
def on_read(method=nil, &blk)
raise "Can't provide both method and block" if method && blk
@on_read = method || blk
end
def on_write(method=nil, &blk)
raise "Can't provide both method and block" if method && blk
@on_write = method || blk
end
def write(writer_name, data, close_on_complete=true)
writer = writer_by_name(writer_name)
buffer_state = @writer_buffers[writer] ||= {
:data => '',
:close_on_complete => nil
}
if buffer_state[:close_on_complete]
raise Rubysh::Error::AlreadyClosedError.new("You have already marked #{writer.inspect} as close_on_complete; can't write more data")
end
buffer_state[:close_on_complete] = close_on_complete
# XXX: unnecessary copy here
buffer_state[:data] += data
# Note that this leads to a bit of weird semantics if you try
# doing a write('') from within an on_write handler, since it'll
# call this synchronously. May want to change at some point.
finalize_writer_if_done(writer)
end
def close(writer_name)
writer = writer_by_name(writer_name)
writer.close
end
def available_readers
potential = @readers.keys - @finished_readers.to_a
potential.select {|reader| !reader.closed?}
end
# Writers with a non-zero number of bytes remaining to write
def available_writers
potential = @writer_buffers.keys - @finished_writers.to_a
potential.select {|writer| !writer.closed? && get_data(writer).length > 0}
end
def run
while available_writers.length > 0 || available_readers.length > 0
run_once
end
end
# This method is a stub so it can be extended in subclasses
def run_once(timeout=nil)
run_select_loop(timeout)
end
def run_select_loop(timeout)
potential_readers = available_readers
potential_writers = available_writers
begin
selected = IO.select(potential_readers, potential_writers, nil, timeout)
rescue Errno::EINTR
retry
else
raise NothingAvailable unless selected
end
ready_readers, ready_writers, _ = selected
$stdout.puts "Stuff: #{ready_readers.inspect}, #{ready_writers.inspect} (total: #{@readers.inspect}"
ready_readers.each do |reader|
read_available(reader)
end
ready_writers.each do |writer|
write_available(writer)
end
end
def consume_all_available
begin
loop {run_select_loop(0)}
rescue NothingAvailable
end
end
def read_available(reader)
begin
data = reader.read_nonblock(4096)
p data
rescue EOFError, Errno::EPIPE
p "done"
finalize_reader(reader)
rescue Errno::EAGAIN, Errno::EWOULDBLOCK, Errno::EINTR
else
issue_reader_callback(reader, data)
end
end
private
def finalize_reader(reader)
@finished_readers.add(reader)
issue_reader_callback(reader, EOF)
reader.close
end
def issue_reader_callback(reader, data)
if @on_read
name = reader_name(reader)
@on_read.call(name, data) if name
end
end
def reader_name(reader)
@readers.fetch(reader)
end
def write_available(writer)
data = get_data(writer)
begin
count = writer.write_nonblock(data)
rescue EOFError, Errno::EPIPE
finalize_writer(writer)
rescue Errno::EAGAIN, Errno::EWOULDBLOCK, Errno::EINTR
else
# XXX: This may be a lot of copying. May want to think about
# how this scales.
written = data[0...count]
remaining = data[count..-1]
set_data(writer, remaining)
issue_writer_callback(writer, written, remaining)
end
finalize_writer_if_done(writer)
end
# Will only schedule a writer if it has a nonzero number of bytes
# left to write, so we need to manually check if we're out after
# every run.
def finalize_writer_if_done(writer)
if !writer.closed? &&
buffer_state(writer)[:close_on_complete] &&
get_data(writer).length == 0
finalize_writer(writer)
end
end
def finalize_writer(writer)
# TODO: think about how we should deal with errors, maybe
remaining = get_data(writer)
@finished_writers.add(writer)
issue_writer_callback(writer, EOF, remaining)
writer.close if buffer_state(writer)[:close_on_complete]
end
def get_data(writer)
buffer_state(writer)[:data]
end
def set_data(writer, data)
buffer_state(writer)[:data] = data
end
def buffer_state(writer)
buffer_state = @writer_buffers[writer]
Rubysh.assert(buffer_state, "No buffer state: #{writer.inspect}", true)
buffer_state
end
def issue_writer_callback(writer, data, remaining)
if @on_write
name = writer_name(writer)
@on_write.call(name, data, remaining) if name
end
end
def writer_name(writer)
@writers.fetch(writer)
end
# Could make this fast, but don't think it matters enough.
def writer_by_name(writer_name)
@writers.detect {|writer, name| writer_name == name}.first
end
end
end