Merge ~seyeongkim/maas:fixing_memory_leak_apt_get_3.2 into maas:3.2

[Seyeong Kim]

Bug #2012596: MAAS 3.2 deb package memory leak after upgrading

(cherry picked from commit d792780dbd0571fcd94e22cb7ce559d5f69aa1a0)

[MAAS Lander (maas-lander)]

UNIT TESTS
-b fixing_memory_leak_apt_get_3.2 lp:~seyeongkim/maas/+git/maas into -b 3.2 lp:~maas-committers/maas

STATUS: SUCCESS
COMMIT: b002af550a84d13d92a3ea46ba28cd7cc710f4a0

review: Approve

[MAAS Lander (maas-lander)]

UNIT TESTS
-b fixing_memory_leak_apt_get_3.2 lp:~seyeongkim/maas/+git/maas into -b 3.2 lp:~maas-committers/maas

STATUS: SUCCESS
COMMIT: b002af550a84d13d92a3ea46ba28cd7cc710f4a0

review: Approve

[Björn Tillenius (bjornt)]

+1

review: Approve

[MAAS Lander (maas-lander)]

LANDING
-b fixing_memory_leak_apt_get_3.2 lp:~seyeongkim/maas/+git/maas into -b 3.2 lp:~maas-committers/maas

STATUS: FAILED BUILD
LOG: http://maas-ci.internal:8080/job/maas-tester/5250/console

diff --git a/src/provisioningserver/utils/deb.py b/src/provisioningserver/utils/deb.py
index 6e0656e..62e9e26 100644
--- a/src/provisioningserver/utils/deb.py
+++ b/src/provisioningserver/utils/deb.py
@@ -14,6 +14,22 @@ maaslog = get_maas_logger("deb")
 
 MAAS_PACKAGES = ("maas-region-api", "maas-rack-controller")
 
+APT_PKG = None
+
+
+def get_apt_pkg():
+    """Return the initalized apt_pkg."""
+    global APT_PKG
+    # Make sure that .init() is only called after initial import.
+    # init() can be slow, and cause memory leaks if called multiple
+    # times.
+    if APT_PKG is None:
+        import apt_pkg
+
+        apt_pkg.init()
+        APT_PKG = apt_pkg
+    return APT_PKG
+
 
 @dataclasses.dataclass
 class DebVersion:
@@ -44,9 +60,7 @@ def get_deb_versions_info(apt_pkg=None) -> Optional[DebVersionsInfo]:
     """Return versions information for Debian-based MAAS."""
 
     if apt_pkg is None:
-        import apt_pkg
-
-        apt_pkg.init()
+        apt_pkg = get_apt_pkg()
 
     try:
         cache = apt_pkg.Cache(None)