tests: check blocking concurrent confdb accesses

Tests that concurrent confdb accesses to the same databag block when
appropriate (no concurrent writes, accesses that can't be parallelized
are serviced in order to prevent starvation) and that it's possible to
supply a timeout.

Signed-off-by: Miguel Pires <miguel.pires@canonical.com>

Author: miguelpires

tests/main/confdb-cross-config/task.yaml

@@ -14,6 +14,7 @@ prepare: |
 
 restore: |
   snap unset system experimental.confdb
+  rm first_read last_read || true
 
 execute: |
   changeAfterID() {
@@ -151,3 +152,39 @@ execute: |
   MATCH 'written-secret-changed' < /var/snap/loading-custodian/common/load-view-manage-wifi-ran
   # but query-view gets the value load-view sets
   MATCH "loaded-secret" < /var/snap/loading-custodian/common/query-view-manage-wifi-ran
+
+  # waiting-custodian will block on write or read ops until a flag is written
+  resetTestState
+  snap disconnect loading-custodian:manage-wifi
+  "$TESTSTOOLS"/snaps-state install-local waiting-custodian
+  snap connect waiting-custodian:wifi-setup
+
+  OLD_CHANGE=$(snap changes | tail -n 2 | head -n 1 | awk '{print $1}')
+  snap set developer1/network-ephemeral/wifi-setup password=initial-password &
+
+  # first change blocks on the save-view-* hook
+  changeAfterID "$OLD_CHANGE"
+  retry -n 5 --wait 1 sh -c 'snap changes | tail -n 2 | grep "Doing.*Set confdb through \"developer1/network-ephemeral/wifi-setup\""'
+  BLOCKED_CHANGE=$(( $OLD_CHANGE + 1 ))
+  snap change "$BLOCKED_CHANGE" | MATCH "Doing.*Run hook save-view-wifi-setup"
+
+  # the access timeout should make this call error without being unblocked
+  timeout -s KILL 2s snap get developer1/network-ephemeral/wifi-setup --wait-for 0s password 2>&1 | tr -d "\n" | tr -s '  ' ' ' |  MATCH "error: cannot read developer1/network-ephemeral/wifi-setup: timed out waiting for access"
+
+  # queue a series of operations that will block on the previous one sequentially
+  sleep 1
+  snap get developer1/network-ephemeral/wifi-setup password > first-read &
+  sleep 1
+  snap set developer1/network-ephemeral/wifi-setup password=last-password &
+  sleep 1
+  snap get developer1/network-ephemeral/wifi-setup password > last-read &
+
+  # unblock the first write and wait for the next operations to complete
+  touch /var/snap/waiting-custodian/common/flag
+  wait
+
+  retry -n 5 --wait 1 sh -c 'snap changes | tail -n 2 | grep "Done.*Get confdb through \"developer1/network-ephemeral/wifi-setup\""'
+
+  # check the operations executed in the expected order
+  MATCH "initial-password" < first-read
+  MATCH "last-password" < last-read

tests/main/confdb-cross-config/waiting-custodian/bin/sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+exec /bin/sh "$@"

tests/main/confdb-cross-config/waiting-custodian/meta/hooks/load-view-wifi-setup

@@ -0,0 +1,5 @@
+#!/bin/sh
+
+until [ -e "$SNAP_COMMON"/flag ]; do
+	sleep 2
+done

tests/main/confdb-cross-config/waiting-custodian/meta/hooks/save-view-wifi-setup

@@ -0,0 +1 @@
+load-view-wifi-setup

tests/main/confdb-cross-config/waiting-custodian/meta/snap.yaml

@@ -0,0 +1,12 @@
+name: waiting-custodian
+version: 1.0
+apps:
+  sh:
+    command: bin/sh
+base: core24
+plugs:
+  wifi-setup:
+    interface: confdb
+    account: developer1
+    view: network-ephemeral/wifi-setup
+    role: custodian