Simple script to monitor the number open file descriptors for an Android application.

watch-fds.sh

#!/bin/sh
# Usage: ./watch-fds.sh <application_id> [delay_secs = 5]

APP_ID=${1:?missing application id}
DELAY=$(( ${2:-5} ))

DEVICE_LIMIT=$(( $(adb shell ulimit -n) ))
WARN_THRESHOLD=$(( ${DEVICE_LIMIT} / 3 ))
echo "Will warn at ${WARN_THRESHOLD}"

APP_PID=$(( $(adb shell ps | grep -m1 "${APP_ID}" | awk '{print $2}') ))
echo "Watching application ${APP_ID} <${APP_PID}>. Press CTRL+C to stop."

fds=""
high_mark=0

while [ true ]; do
  app_proc=$(( $(adb shell ps ${APP_PID} | grep -c ${APP_ID}) ))

  if [ ${app_proc} -ne 1 ]; then
    echo "Process ${APP_ID} <${APP_PID}> has died."
    echo "Last list of File Descriptors:"
    echo "${fds}"
    exit
  fi

  fds="$(adb shell run-as ${APP_ID} ls -l /proc/${APP_PID}/fd 2>/dev/null)"
  fd_count=$(( $(wc -l <<< "${fds}") ))

  echo ${fd_count}

  if [ ${fd_count} -ge ${WARN_THRESHOLD} -a ${fd_count} -gt ${high_mark} ]; then
    echo " *** *** *** "
    echo "Warning: FD count > warning threshold: ${fd_count}"
    # echo "Current File Descriptors:"
    # echo "${fds}"
    echo " *** *** *** "
    echo ""
    # then ratchet the highwater mark
    high_mark=$(( ${fd_count} ))
  fi

  sleep ${DELAY}
done