Backport #5539
closed
Readline.readline() blocks all threads
Description
The standard library Readline.readline() function blocks the thread it's called from without unlocking the VM, thus blocking all threads. This code demonstrates the problem:
require 'pp'
t = Thread.new {10.times {|x| puts x; sleep 1}}
while(buf = Readline.readline)
p buf
if(buf == 'q')
break
end
end
Thread t will be blocked by the readline call, numbers being printed occasionally when lines are entered and readline() returns, rather than once per second. Reproduced on ruby 1.9.2p180 (2011-02-18 revision 30909) [x86_64-darwin10.6.0] and ruby 1.9.3p0 (2011-10-30 revision 33570) [x86_64-darwin10.8.0].
The RubyInline gem allows a workaround:
require 'inline'
class BetterReadline
inline :C do |builder|
builder.include '<ruby.h>'
builder.include '<readline/readline.h>'
src = <<END
VALUE readline_intern(void * data) {
char ** rstr = (char **)data;
*rstr = readline(NULL);
return Qnil;
}
END
builder.prefix(src)
src = <<END
VALUE rb_readline(void) {
char * str = NULL;
rb_thread_blocking_region(readline_intern, &str, NULL, NULL);
return rb_str_new2(str);
}
END
builder.c_singleton(src, method_name: 'readline')
end
end # class BetterReadline
This then illustrates the desired behavior, with the thread running in the background while readline() waits for input:
require 'pp'
t = Thread.new {10.times {|x| puts x; sleep 1}}
while(buf = BetterReadline.readline)
p buf
if(buf == 'q')
break
end
end
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