Upload to Leonardo sometimes fails with Permission denied

[dimich-dmb]

Forcing reset using 1200bps open/close on port /dev/ttyACM0
PORTS {/dev/ttyACM0, /dev/ttyS0, /dev/ttyS4, /dev/ttyS5, } / {/dev/ttyS0, /dev/ttyS4, /dev/ttyS5, } => {}
PORTS {/dev/ttyS0, /dev/ttyS4, /dev/ttyS5, } / {/dev/ttyACM0, /dev/ttyS0, /dev/ttyS4, /dev/ttyS5, } => {/dev/ttyACM0, }
Found upload port: /dev/ttyACM0
//bin/avrdude -C//etc/avrdude.conf -v -patmega32u4 -cavr109 -P/dev/ttyACM0 -b57600 -D -Uflash:w:/tmp/arduino_build_862951/semaphore.ino.hex:i.

avrdude: Version 7.0
         Copyright (c) Brian Dean, http://www.bdmicro.com/
         Copyright (c) Joerg Wunsch

         System wide configuration file is "//etc/avrdude.conf"
         User configuration file is "/home/dimich/.avrduderc"
         User configuration file does not exist or is not a regular file, skipping

         Using Port                    : /dev/ttyACM0
         Using Programmer              : avr109
         Overriding Baud Rate          : 57600
avrdude: ser_open(): can't open device "/dev/ttyACM0": Permission denied
avrdude: opening programmer "avr109" on port "/dev/ttyACM0" failed

This happens because udev applies permissions to device files non-atomically: first it creates /dev/ACM* with root:root ownership and then GROUP="uucp" is applied. When SerialUploader detects port appearence it invokes avrdude immediately, even if ownership/permissions aren't yet applied.

Possible solution is to wait for port is accessible, e.g. with access(port, R_OK | W_OK).

[cropinghigh]

Same problem on Manjaro with udev rule