IO.select accepts +Float::INFINITY+ as a timeout argument.

matz accepted at the developper meeting 2024-07-11.

Author: akr

NEWS.md

@@ -20,6 +20,11 @@ Note: We're only listing outstanding class updates.
       Also, `Binding#local_variable_get` and `Binding#local_variable_set` reject to handle numbered parameters.
       [[Bug #21049]]
 
+* IO
+
+    * `IO.select` accepts +Float::INFINITY+ as a timeout argument.
+      [[Feature #20610]]
+
 * String
 
     * Update Unicode to Version 15.1.0 and Emoji Version 15.1. [[Feature #19908]]

io.c

@@ -10993,6 +10993,16 @@ rb_io_advise(int argc, VALUE *argv, VALUE io)
 #endif
 }
 
+static int
+is_pos_inf(VALUE x)
+{
+  double f;
+  if (!RB_FLOAT_TYPE_P(x))
+    return 0;
+  f = RFLOAT_VALUE(x);
+  return isinf(f) && 0 < f;
+}
+
 /*
  *  call-seq:
  *    IO.select(read_ios, write_ios = [], error_ios = [], timeout = nil) -> array or nil
@@ -11009,6 +11019,8 @@ rb_io_advise(int argc, VALUE *argv, VALUE io)
  *
  *  Argument +timeout+ is a numeric value (such as integer or float) timeout
  *  interval in seconds.
+ *  +timeout+ can also be +nil+ or +Float::INFINITY+.
+ *  +nil+ and +Float::INFINITY+ means no timeout.
  *
  *  The method monitors the \IO objects given in all three arrays,
  *  waiting for some to be ready;
@@ -11159,7 +11171,7 @@ rb_f_select(int argc, VALUE *argv, VALUE obj)
     int i;
 
     rb_scan_args(argc, argv, "13", &args.read, &args.write, &args.except, &timeout);
-    if (NIL_P(timeout)) {
+    if (NIL_P(timeout) || is_pos_inf(timeout)) {
         args.timeout = 0;
     }
     else {

test/ruby/test_io.rb

@@ -4262,6 +4262,23 @@ def test_select_exceptfds
     end
   end if Socket.const_defined?(:MSG_OOB)
 
+  def test_select_timeout
+    assert_equal(nil, IO.select(nil,nil,nil,0))
+    assert_equal(nil, IO.select(nil,nil,nil,0.0))
+    assert_raise(TypeError) { IO.select(nil,nil,nil,"invalid-timeout") }
+    assert_raise(ArgumentError) { IO.select(nil,nil,nil,-1) }
+    assert_raise(ArgumentError) { IO.select(nil,nil,nil,-0.1) }
+    assert_raise(ArgumentError) { IO.select(nil,nil,nil,-Float::INFINITY) }
+    assert_raise(RangeError) { IO.select(nil,nil,nil,Float::NAN) }
+    IO.pipe {|r, w|
+      w << "x"
+      ret = [[r], [], []]
+      assert_equal(ret, IO.select([r],nil,nil,0.1))
+      assert_equal(ret, IO.select([r],nil,nil,1))
+      assert_equal(ret, IO.select([r],nil,nil,Float::INFINITY))
+    }
+  end
+
   def test_recycled_fd_close
     dot = -'.'
     IO.pipe do |sig_rd, sig_wr|