GCS based locking function

lock-funcs.txt

#! /usr/bin/env bash
set -u

# constants
PROJECT=$(gcloud info --format='value(config.project)')
LOCKS_BUCKET=$PROJECT-db2-locks
# how long do we wait for lock or condition
SLEEP=5

# Check if a lock file exists
# Globals:
#   None
# Arguments:
#   LOCK_FILE_URL
# Returns:
#   0 
function no_lock_yet() {
  local LOCK_FILE_URL="$1"
  # blocking till the lock is released by some other process
  until ! gsutil ls $LOCK_FILE_URL >/dev/null 2>&1; do
    sleep "${SLEEP}"
  done
  # no lock any more
  echo 0
}

function lock() {
  local LOCK_FILE_PREFIX="$1"
  local LOCK_FILE="$2"
  local LOCK_FILE_URL=gs://$LOCKS_BUCKET/$LOCK_FILE_PREFIX/$LOCK_FILE

  # ONLY lock if there is no lock file exists
  # mkdir -p the prefix and geneate the lock file, then rsync over to GCS
  if ! gsutil ls "$LOCK_FILE_URL" >/dev/null 2>&1;then
    local TEMP_DIR=$(mktemp -d)
    local LOCK_DIR=${TEMP_DIR}/${LOCK_FILE_PREFIX}
    mkdir -p $LOCK_DIR && touch $LOCK_DIR/$LOCK_FILE
    (cd $TEMP_DIR && gsutil rsync -r . gs://$LOCKS_BUCKET)
  else
    echo "lock $LOCK_FILE_PREFIX/$LOCK_FILE exists already"
  fi
}

# Acquire a lock
# Globals:
#   LOCKS_BUCKET
# Arguments:
#   (ENV,DB_INSTANCE_NAME,DB_NAME,LOCK_FILE)
# Returns:
#   0 
# blocking till we can lock 
function db2_acquire_lock() {
   local ENV=$1
   local DB_INSTANCE_NAME=$2
   local DB_NAME=$3
   local LOCK_FILE=$4
   local LOCK_FILE_PREFIX=${ENV}/${DB_INSTANCE_NAME}/${DB_NAME}
   local LOCK_FILE_URL=gs://$LOCKS_BUCKET/$LOCK_FILE_PREFIX/$LOCK_FILE
   free_to_lock=$(no_lock_yet $LOCK_FILE_URL)
   #  echo "free_to_lock is $free_to_lock"
   if [[ $free_to_lock -eq 0 ]];then
      echo "$LOCK_FILE_URL is free to lock"
      lock $LOCK_FILE_PREFIX $LOCK_FILE
   fi
}

# Release a lock
# Globals:
#   LOCKS_BUCKET
# Arguments:
#   (ENV,DB_INSTANCE_NAME,DB_NAME,LOCK_FILE)
# Returns:
#   0 
function db2_release_lock() {
   local ENV=$1
   local DB_INSTANCE_NAME=$2
   local DB_NAME=$3
   local LOCK_FILE=$4
   local LOCK_FILE_PREFIX=${ENV}/${DB_INSTANCE_NAME}/${DB_NAME}
   local LOCK_FILE_URL=gs://$LOCKS_BUCKET/$LOCK_FILE_PREFIX/$LOCK_FILE

   # release the lock if there is a one
   if gsutil ls "$LOCK_FILE_URL" >/dev/null 2>&1;then
     echo "unlock $LOCK_FILE_URL"
     gsutil rm "$LOCK_FILE_URL"
     # error check here
  fi
}

# wait for a lock to be acquired
# Globals:
#   LOCKS_BUCKET
# Arguments:
#   (ENV,DB_INSTANCE_NAME,DB_NAME,LOCK_FILE)
# Returns:
#   0 
function wait_for() {
  local ENV=$1
  local DB_INSTANCE_NAME=$2
  local DB_NAME=$3
  local LOCK_FILE=$4
  local LOCK_FILE_PREFIX=${ENV}/${DB_INSTANCE_NAME}/${DB_NAME}
  local LOCK_FILE_URL=gs://$LOCKS_BUCKET/$LOCK_FILE_PREFIX/$LOCK_FILE
  # blocking till the lock is acquired by some other process
  until gsutil ls $LOCK_FILE_URL >/dev/null 2>&1; do
    echo "wait_for $LOCK_FILE_URL"
    sleep "${SLEEP}"
  done
}

# notify that a lock is acquired
# Globals:
#   LOCKS_BUCKET
# Arguments:
#   (ENV,DB_INSTANCE_NAME,DB_NAME,LOCK_FILE)
# Returns:
#   0 
function notify() {
  local ENV=$1
  local DB_INSTANCE_NAME=$2
  local DB_NAME=$3
  local LOCK_FILE=$4
  local LOCK_FILE_PREFIX=${ENV}/${DB_INSTANCE_NAME}/${DB_NAME}
  local LOCK_FILE_URL=gs://$LOCKS_BUCKET/$LOCK_FILE_PREFIX/$LOCK_FILE
  lock $LOCK_FILE_PREFIX $LOCK_FILE
}

# test functions below
# function test_lock() {
#   local LOCK_FILE_PREFIX=dev/primary-dbi-1/db-1
#   lock $LOCK_FILE_PREFIX lock-1
#   lock $LOCK_FILE_PREFIX lock-2
# }


# create the bucket for testing
if ! gsutil ls "gs://${LOCKS_BUCKET}";then
    gsutil mb -c regional -l us-central1 gs://${LOCKS_BUCKET}
fi 

# test the func used by the main backup script
#db2_acquire_lock dev primary-dbi-1 db-1 lock-backup
# gsutil ls -r gs://${LOCKS_BUCKET}
# test_release_lock
#db2_release_lock dev primary-dbi-1 db-1 lock-backup
# gsutil ls -r gs://${LOCKS_BUCKET}

# test_wait_for
#wait_for dev primary-dbi-1 db-1 lock-primary-ready
# gsutil ls -r gs://${LOCKS_BUCKET}
# test_notify
#notify dev primary-dbi-1 db-1 lock-primary-ready
# gsutil ls -r gs://${LOCKS_BUCKET}