how to prevent deadlock on this... Post: 86175

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Top Forums Programming how to prevent deadlock on this... Post 86175 by Perderabo on Tuesday 11th of October 2005 08:57:51 PM

10-11-2005

Administrator Emeritus

You are setting the O_NDELAY flag on the open(). That is a bad idea for several reasons. The newer O_NONBLOCK flag corrects a problem with O_NDELAY. Use O_NONBLOCK for new code. Setting either flag means that the open() call itself will not hang. But subsequent operations on the fd are being affected. Posix says, about O_NONBLOCK, "When opening a block special or character special file that supports non-blocking opens: Subsequent behavior of the device is device-specific." The Linux man page says, "Neither the open nor any subsequent operations on the file descriptor which is returned will cause the calling process to wait".

These flags are affecting read(). The read will return immediately if no characters are available. The old O_NDELAY will return a zero in this case. That is the same thing EOF would return... this is the problem with that flag. If O_NONBLOCK is set, -1 is returned with errno set to EAGAIN.

So my advice: use O_NONBLOCK for the open and then turn it off... something like this:
flags=fcntl(fd, F_GETFL, 0);
flags &= ~O_NONBLOCK;
fcnt(fd, F_SETFL,flags);

Next, you mention that you are setting termios paramters. Take a look at CMIN and CTIME. You can use them to control when the read returns. That means you can get rid of select().

You may still need to do more than one read. Use an overall loop...something like:

Code:

nbytes=16;
nreads=5;
ptr=buffer;
for (nreads=5; nbytes && nreads; nreads--)  {
        iret = read(fd, ptr, nbytes);
        if (iret > 0) {
                ptr += iret;
                nbytes -= iret;
        }
}

Of course, you will need to check the sys calls for failure. I'm just sketching in the basic flow, not writing real code.

Perderabo

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input-linux-mouse

input-linux-mouse(7)							GGI						      input-linux-mouse(7)

NAME

       input-linux-mouse - Direct mouse input

SYNOPSIS

       input-linux-mouse: [<mousetype>] [,<file>] [,[b<bauds>][r<rts>][d<dtr>]]

DESCRIPTION

       This input opens a file (usually a device file or pipe) and reads mouse protocol data from it.

OPTIONS

       mousetype
	      Indicates what type of mouse is attached.  The following types are supported:

	      o   ms, Microsoft : Two button Microsoft compatible mice.

	      o   ms3, IntelliMouse, mman+ : Serial Intellimouse or compatible. Supports four buttons for mice like the Logitech MouseMan+.

	      o   MouseSystems, msc : MouseSystems compatible (used in most 3-button mice).

	      o   Logitech, logi :  Used in older Logitech serial mice.

	      o   mm, MMSeries :    MM series mice.

	      o   Sun : Sun mice. The protocol is the same as 'msc' protocol except it used only 3 bytes per packet.

	      o   MouseMan, mman :  MouseMan protocol.

	      o   BusMouse, bm : Non-PS/2 busmice.

	      o   LinuxUSB, lnxusb : IMPS2 that doesn't choke on USB (no init attempted).

	      o   ps2, PS/2 : PS/2 mice (most non-serial mice use this protocol)

	      o   imps2, IMPS/2 : PS/2 IntelliMouse and compatible (not USB, see lnxusb for that.)

	      o   mmanps2, MouseManPlusPS/2 : PS/2 Logitech MouseMan+ and compatible.

	      Most of the strings supported by GPM, SVGAlib and XFree can be specified.  If you find one that isn't, please report.

	      The  special  value  auto  tells input-linux-mouse to read ~/.ggi/input/linux-mouse, and if that fails, $sysconfdir/ggi/input/linux-
	      mouse.  If none of the two files are found, input-linux-mouse tries to auto-detect the mouse, and as a last resort  uses	the  mouse
	      information specified in /etc/vga/libvga.config.

       file   The file to read mouse protocol data from; defaults to /dev/mouse.

       baud   Baud rate of mouse device.

       rts    Turns off RTS if set to 0; turns RTS on if set to a number greater than 0.

       dtr    Turns off DTR if set to 0; turns DTR on if set to a number greater than 0.

FEATURES

       o   Generates evPtr* events.

FILES

       ~/.ggi/input/linux-mouse and $sysconfdir/ggi/input/linux-mouse consists of the following entries:

       mouse mousetype
       mdev file

       where mousetype and file has the same semantics as the invocation options of the same names.

libgii-1.0.x							    2003-08-11						      input-linux-mouse(7)

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