# Copyright (c) 2021 Digital Asset (Switzerland) GmbH and/or its affiliates. All rights reserved.
# SPDX-License-Identifier: Apache-2.0

# We have a number of tests that require spawning and then destroying an
# instance of a PostgreSQL server. PostgreSQL uses a shared memory segment to
# coordinate between internal threads. On macOS (and maybe other platforms, but
# macOS is the one where we observed the issue), about one in three times Bazel
# stops a PostgreSQL server, the shared memory segment does not get reclaimed.
# Over time, the shared memory gets full and the machine is not able to start
# new instances of PostgreSQL until it gets rebooted. Given that we do not have
# an easy way to reboot macOS nodes, this is a Bad Thing™.
#
# This simple script will mark all of the existing shared memory segments on
# the machine for deletion. This has not been extensively tested and may cause
# issues. It seems safe enough for now because:
#
# 1. We currently do not run any other application than PostgreSQL that uses
# shared memory segments on CI, and
#
# 2. The command, despite the `rm` in its name, does not actually delete the
# memory segments, but simply marks them for reclamation. They will be kept for
# as long as there is at least one process connected to them. Since PostgreSQL,
# at least in the configuration we are using, runs from a single process, this
# is safe to run even while PostgreSQL is still running (Works On My Machine®).
# Segments do get deleted immediately if there is no process connected to them
# when the command is run.

steps:
- bash: |
    set -euo pipefail

    # ipcs -m prints a three-line human-friendly header then all memory
    # segments in a tabular format. The second column holds the segment IDs,
    # which is what ipcrm expects as its arguments. After the table, ipcs -m
    # adds an extra blank line, hence the extra sed at the end.
    for shmid in $(ipcs -m | sed 1,3d | awk '{print $2}' | sed '$d'); do
      # Some memory segments cannot be removed and fail with "invalid argument".
      # We just ignore those for now instead of failing CI.
      ipcrm -m $shmid || true
    done
  name: clear_shm