Default to nonblocking whenever possible

core/src/main/java/org/jruby/RubyIO.java

@@ -905,6 +905,15 @@ private IRubyObject initializeCommon(ThreadContext context, int fileno, IRubyObj
                     }
                 }
             }
+
+            // set to nonblocking if possible (Ruby 3.0 change for IO/fiber scheduling)
+            if (fd.chSelect != null) {
+                try {
+                    fd.chSelect.configureBlocking(false);
+                } catch (IOException ioe) {
+                    // ignore, can't set nonblocking
+                }
+            }
         } else {
             fd = runtime.getFilenoUtil().getWrapperFromFileno(fileno);
 
@@ -4173,6 +4182,7 @@ private void setupPopen(final Ruby runtime, ModeFlags modes, POpenProcess proces
             ChannelFD main = new ChannelFD(inChannel, runtime.getPosix(), runtime.getFilenoUtil());
 
             openFile.setFD(main);
+            openFile.setBlocking(runtime, false);
         }
 
         if (openFile.isWritable() && process.hasOutput()) {
@@ -4195,6 +4205,7 @@ private void setupPopen(final Ruby runtime, ModeFlags modes, POpenProcess proces
                 setInstanceVariable("@tied_io_for_writing", writeIO);
             } else {
                 openFile.setFD(pipe);
+                openFile.setBlocking(runtime, false);
             }
         }
     }

core/src/main/java/org/jruby/ext/socket/RubyBasicSocket.java

@@ -892,6 +892,7 @@ protected void initSocket(ChannelFD fd) {
         MakeOpenFile();
 
         openFile.setFD(fd);
+        openFile.setBlocking(getRuntime(), false);
         openFile.setMode(OpenFile.READWRITE | OpenFile.SYNC);
 
         // see rsock_init_sock in MRI; sockets are initialized to binary

core/src/main/java/org/jruby/ext/socket/RubyUNIXSocket.java

@@ -391,6 +391,7 @@ protected void init_sock(Ruby runtime, Channel channel, String path) {
         ModeFlags modes = newModeFlags(runtime, ModeFlags.RDWR);
 
         openFile.setFD(newChannelFD(runtime, channel));
+        openFile.setBlocking(runtime, false);
         openFile.setMode(modes.getOpenFileFlags());
         openFile.setSync(true);
         openFile.setPath(path);

core/src/main/java/org/jruby/util/io/OpenFile.java

@@ -192,10 +192,18 @@ public boolean IS_PREP_STDIO() {
 
     public void setFD(ChannelFD fd) {
         this.fd = fd;
+        updateBlockingFromFD(fd);
     }
 
     public void setChannel(Channel fd) {
         this.fd = new ChannelFD(fd, runtime.getPosix(), runtime.getFilenoUtil());
+        updateBlockingFromFD(this.fd);
+    }
+
+    private void updateBlockingFromFD(ChannelFD fd) {
+        if (fd.chSelect != null ) {
+            this.nonblock = !fd.chSelect.isBlocking();
+        }
     }
 
     public int getMode() {