Merge pull request #9792 from poettering/hashmap-mempool

minor hashmap fixes

31 files changed, 127 insertions, 139 deletions

diff --git a/TODO b/TODO
index 3ca3c5ec35..9d3a4d13b6 100644
--- a/TODO
+++ b/TODO
@@ -23,6 +23,13 @@ Janitorial Clean-ups:
 
 Features:
 
+* optionally, if a per-partition GPT flag is set for the root/home/… partitions
+  format the partition on next boot and unset the flag, in order to implement
+  factory reset. also, add a second flag that simply indicates whether such a
+  scheme is supported. then, add a tool (or maybe beef up systemd-dissect) to
+  show state of these flags, and optionally trigger such a factory reset on
+  next boot by setting the flag.
+
 * logind: maybe watch utmp asynchronously using inotify, and populate our own
   tracked session metadata from the fields available therein. Why bother? Right
   now, all "ssh" sessions will be tracked without their TTY by logind (which is
diff --git a/doc/ENVIRONMENT.md b/doc/ENVIRONMENT.md
index c69bf9b664..9d598a6693 100644
--- a/doc/ENVIRONMENT.md
+++ b/doc/ENVIRONMENT.md
@@ -42,6 +42,9 @@ All tools:
   are understood, too (us, ms, s, min, h, d, w, month, y). If it is not set or set
   to 0, then the built-in default is used.
 
+* `$SYSTEMD_MEMPOOL=0` — if set the internal memory caching logic employed by
+  hash tables is turned off, and libc malloc() is used for all allocations.
+
 systemctl:
 
 * `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus
diff --git a/man/libudev.xml b/man/libudev.xml
index 8cb4ba59fc..382c1aa25c 100644
--- a/man/libudev.xml
+++ b/man/libudev.xml
@@ -48,11 +48,9 @@
     <citerefentry><refentrytitle>udev_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
     It is used to track library state and link objects together. No
     global state is used by libudev, everything is always linked to
-    a udev context. Furthermore, multiple different udev contexts can
-    be used in parallel by multiple threads. However, a single context
-    must not be accessed by multiple threads in parallel. The caller
-    is responsible for providing suitable locking if they intend to use
-    it from multiple threads.</para>
+    a udev context.</para>
+
+    <xi:include href="threads-aware.xml" xpointer="strict"/>
 
     <para>To introspect a local device on a system, a udev device
     object can be created via
diff --git a/man/sd-bus-errors.xml b/man/sd-bus-errors.xml
index 50abf4c076..c896511541 100644
--- a/man/sd-bus-errors.xml
+++ b/man/sd-bus-errors.xml
@@ -6,7 +6,8 @@
   SPDX-License-Identifier: LGPL-2.1+
 -->
 
-<refentry id="sd-bus-errors">
+<refentry id="sd-bus-errors"
+          xmlns:xi="http://www.w3.org/2001/XInclude">
 
   <refentryinfo>
     <title>sd-bus-errors</title>
@@ -259,15 +260,7 @@
     </variablelist>
   </refsect1>
 
-  <refsect1>
-    <title>Notes</title>
-
-    <para>The various error definitions described here are available
-    as a shared library, which can be compiled and linked to with the
-    <constant>libsystemd</constant> <citerefentry
-    project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
-    file.</para>
-  </refsect1>
+  <xi:include href="libsystemd-pkgconfig.xml" />
 
   <refsect1>
     <title>See Also</title>
diff --git a/man/sd-journal.xml b/man/sd-journal.xml
index 8bfcb90ca0..3fa6c75b7e 100644
--- a/man/sd-journal.xml
+++ b/man/sd-journal.xml
@@ -77,16 +77,15 @@
   <refsect1>
     <title>Thread safety</title>
 
-    <para>Functions that operate on the <structname>sd_journal</structname> object are thread
-    agnostic — given <structname>sd_journal</structname> pointer may only be used from one thread at
-    a time, but multiple threads may use multiple such objects safely. Other functions —
-    those that are used to send entries to the journal, like
-    <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>
-    and similar, or those that are used to retrieve global information like
-    <citerefentry><refentrytitle>sd_journal_stream_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>
-    and
+    <para>Functions that operate on <structname>sd_journal</structname> objects are thread agnostic — given
+    <structname>sd_journal</structname> pointer may only be used from one specific thread at all times (and it has to
+    be the very same one during the entire lifetime of the object), but multiple, independent threads may use multiple,
+    independent objects safely. Other functions — those that are used to send entries to the journal, like
+    <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry> and similar,
+    or those that are used to retrieve global information like
+    <citerefentry><refentrytitle>sd_journal_stream_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
     <citerefentry><refentrytitle>sd_journal_get_catalog_for_message_id</refentrytitle><manvolnum>3</manvolnum></citerefentry>
-    — are thread-safe and may be called from multiple threads in parallel.</para>
+    — are fully thread-safe and may be called from multiple threads in parallel.</para>
   </refsect1>
 
   <xi:include href="libsystemd-pkgconfig.xml" />
diff --git a/man/sd_bus_add_match.xml b/man/sd_bus_add_match.xml
index a22d443ce7..c4f24aed3e 100644
--- a/man/sd_bus_add_match.xml
+++ b/man/sd_bus_add_match.xml
@@ -8,7 +8,7 @@
   Copyright © 2016 Julian Orth
 -->
 
-<refentry id="sd_bus_add_match">
+<refentry id="sd_bus_add_match" xmlns:xi="http://www.w3.org/2001/XInclude">
 
   <refentryinfo>
     <title>sd_bus_add_match</title>
@@ -154,9 +154,7 @@
   <refsect1>
     <title>Notes</title>
 
-    <para><function>sd_bus_add_match()</function> and the other functions described here are available as a shared
-    library, which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry
-    project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
+    <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
   </refsect1>
 
   <refsect1>
diff --git a/man/sd_bus_error_add_map.xml b/man/sd_bus_error_add_map.xml
index 107291f26f..dbe05a1892 100644
--- a/man/sd_bus_error_add_map.xml
+++ b/man/sd_bus_error_add_map.xml
@@ -6,7 +6,8 @@
   SPDX-License-Identifier: LGPL-2.1+
 -->
 
-<refentry id="sd_bus_error_add_map">
+<refentry id="sd_bus_error_add_map"
+          xmlns:xi="http://www.w3.org/2001/XInclude">
 
   <refentryinfo>
     <title>sd_bus_error_add_map</title>
@@ -123,15 +124,7 @@
     </variablelist>
   </refsect1>
 
-  <refsect1>
-    <title>Notes</title>
-
-    <para>The various error definitions described here are available
-    as a shared library, which can be compiled and linked to with the
-    <constant>libsystemd</constant> <citerefentry
-    project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
-    file.</para>
-  </refsect1>
+  <xi:include href="libsystemd-pkgconfig.xml" />
 
   <refsect1>
     <title>See Also</title>
diff --git a/man/sd_bus_is_open.xml b/man/sd_bus_is_open.xml
index 5cd2d18c4d..0388db82a6 100644
--- a/man/sd_bus_is_open.xml
+++ b/man/sd_bus_is_open.xml
@@ -6,7 +6,8 @@
   SPDX-License-Identifier: LGPL-2.1+
 -->
 
-<refentry id="sd_bus_is_open">
+<refentry id="sd_bus_is_open"
+          xmlns:xi="http://www.w3.org/2001/XInclude">
 
   <refentryinfo>
     <title>sd_bus_is_open</title>
@@ -88,13 +89,7 @@
     </variablelist>
   </refsect1>
 
-  <refsect1>
-    <title>Notes</title>
-
-    <para><function>sd_bus_is_open()</function> and <function>sd_bus_is_ready()</function> are available as
-    a shared library, which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry
-    project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
-  </refsect1>
+  <xi:include href="libsystemd-pkgconfig.xml" />
 
   <refsect1>
     <title>See Also</title>
diff --git a/man/sd_bus_path_encode.xml b/man/sd_bus_path_encode.xml
index 4c60a8fa3e..03130a697b 100644
--- a/man/sd_bus_path_encode.xml
+++ b/man/sd_bus_path_encode.xml
@@ -6,7 +6,7 @@
   SPDX-License-Identifier: LGPL-2.1+
 -->
 
-<refentry id="sd_bus_path_encode">
+<refentry id="sd_bus_path_encode" xmlns:xi="http://www.w3.org/2001/XInclude">
 
   <refentryinfo>
     <title>sd_bus_path_encode</title>
@@ -141,15 +141,7 @@
     by the caller.</para>
   </refsect1>
 
-  <refsect1>
-    <title>Notes</title>
-
-    <para><function>sd_bus_path_encode()</function> and
-    <function>sd_bus_path_decode()</function> are available as a
-    shared library, which can be compiled and linked to with the
-    <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
-    file.</para>
-  </refsect1>
+  <xi:include href="libsystemd-pkgconfig.xml" />
 
   <refsect1>
     <title>See Also</title>
diff --git a/man/sd_bus_request_name.xml b/man/sd_bus_request_name.xml
index 54a14c877c..3c98b60c6a 100644
--- a/man/sd_bus_request_name.xml
+++ b/man/sd_bus_request_name.xml
@@ -6,7 +6,8 @@
   SPDX-License-Identifier: LGPL-2.1+
 -->
 
-<refentry id="sd_bus_request_name">
+<refentry id="sd_bus_request_name"
+          xmlns:xi="http://www.w3.org/2001/XInclude">
 
   <refentryinfo>
     <title>sd_bus_request_name</title>
@@ -193,13 +194,7 @@
     </variablelist>
   </refsect1>
 
-  <refsect1>
-    <title>Notes</title>
-
-    <para>The <function>sd_bus_acquire_name()</function> and the other interfaces described here are available as a
-    shared library, which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry
-    project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
-  </refsect1>
+  <xi:include href="libsystemd-pkgconfig.xml" />
 
   <refsect1>
     <title>See Also</title>
diff --git a/man/sd_bus_set_connected_signal.xml b/man/sd_bus_set_connected_signal.xml
index 9dd47bc4df..32fc630cfe 100644
--- a/man/sd_bus_set_connected_signal.xml
+++ b/man/sd_bus_set_connected_signal.xml
@@ -6,7 +6,8 @@
   SPDX-License-Identifier: LGPL-2.1+
 -->
 
-<refentry id="sd_bus_set_connected_signal">
+<refentry id="sd_bus_set_connected_signal"
+          xmlns:xi="http://www.w3.org/2001/XInclude">
 
   <refentryinfo>
     <title>sd_bus_set_connected_signal</title>
@@ -94,13 +95,7 @@
     </variablelist>
   </refsect1>
 
-  <refsect1>
-    <title>Notes</title>
-
-    <para><function>sd_bus_set_connected_signal()</function> and <function>sd_bus_get_connected_signal()</function> are available as
-    a shared library, which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry
-    project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
-  </refsect1>
+  <xi:include href="libsystemd-pkgconfig.xml" />
 
   <refsect1>
     <title>See Also</title>
diff --git a/man/sd_bus_set_sender.xml b/man/sd_bus_set_sender.xml
index 512fffcf05..556e72cefc 100644
--- a/man/sd_bus_set_sender.xml
+++ b/man/sd_bus_set_sender.xml
@@ -6,7 +6,8 @@
   SPDX-License-Identifier: LGPL-2.1+
 -->
 
-<refentry id="sd_bus_set_sender">
+<refentry id="sd_bus_set_sender"
+          xmlns:xi="http://www.w3.org/2001/XInclude">
 
   <refentryinfo>
     <title>sd_bus_set_sender</title>
@@ -89,13 +90,7 @@
     </variablelist>
   </refsect1>
 
-  <refsect1>
-    <title>Notes</title>
-
-    <para><function>sd_bus_set_sender()</function> and <function>sd_bus_get_sender()</function> are available as
-    a shared library, which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry
-    project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
-  </refsect1>
+  <xi:include href="libsystemd-pkgconfig.xml" />
 
   <refsect1>
     <title>See Also</title>
diff --git a/man/sd_bus_set_watch_bind.xml b/man/sd_bus_set_watch_bind.xml
index 41a4bc27dc..129b98c5f3 100644
--- a/man/sd_bus_set_watch_bind.xml
+++ b/man/sd_bus_set_watch_bind.xml
@@ -6,7 +6,8 @@
   SPDX-License-Identifier: LGPL-2.1+
 -->
 
-<refentry id="sd_bus_set_watch_bind">
+<refentry id="sd_bus_set_watch_bind"
+          xmlns:xi="http://www.w3.org/2001/XInclude">
 
   <refentryinfo>
     <title>sd_bus_set_watch_bind</title>
@@ -100,13 +101,7 @@
     </variablelist>
   </refsect1>
 
-  <refsect1>
-    <title>Notes</title>
-
-    <para><function>sd_bus_set_watch_bind()</function> and <function>sd_bus_get_watch_bind()</function> are available as
-    a shared library, which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry
-    project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
-  </refsect1>
+  <xi:include href="libsystemd-pkgconfig.xml" />
 
   <refsect1>
     <title>See Also</title>
diff --git a/man/sd_journal_enumerate_fields.xml b/man/sd_journal_enumerate_fields.xml
index 95af2c1ee0..c5704f53ad 100644
--- a/man/sd_journal_enumerate_fields.xml
+++ b/man/sd_journal_enumerate_fields.xml
@@ -86,8 +86,7 @@
   <refsect1>
     <title>Notes</title>
 
-    <para>All functions listed here are thread-agnostic and only a single thread may operate
-    on a given <structname>sd_journal</structname> object.</para>
+    <xi:include href="threads-aware.xml" xpointer="strict" />
 
     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
   </refsect1>
diff --git a/man/sd_journal_get_catalog.xml b/man/sd_journal_get_catalog.xml
index ce37e177bd..80edc08c81 100644
--- a/man/sd_journal_get_catalog.xml
+++ b/man/sd_journal_get_catalog.xml
@@ -87,9 +87,14 @@
   <refsect1>
     <title>Notes</title>
 
-    <para>Function <function>sd_journal_get_catalog()</function> is thread-agnostic and only a
-    single thread may operate on a given <structname>sd_journal</structname> object. Function
-    <function>sd_journal_get_catalog_for_message_id()</function> is thread-safe.</para>
+    <para>Function <function>sd_journal_get_catalog()</function> is thread-agnostic and only
+    a single specific thread may operate on a given object during its entire lifetime. It's safe to allocate multiple
+    independent objects and use each from a specific thread in parallel. However, it's not safe to allocate such an
+    object in one thread, and operate or free it from any other, even if locking is used to ensure these threads don't
+    operate on it at the very same time.</para>
+
+    <para>Function <function>sd_journal_get_catalog_for_message_id()</function> is are thread-safe and may be called in
+    parallel from multiple threads.</para>
 
     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
   </refsect1>
diff --git a/man/sd_journal_get_cursor.xml b/man/sd_journal_get_cursor.xml
index 6817a3cd54..d5e465b81a 100644
--- a/man/sd_journal_get_cursor.xml
+++ b/man/sd_journal_get_cursor.xml
@@ -98,8 +98,7 @@
   <refsect1>
     <title>Notes</title>
 
-    <para>All functions listed here are thread-agnostic and only a single thread may operate
-    on a given <structname>sd_journal</structname> object.</para>
+    <xi:include href="threads-aware.xml" xpointer="strict" />
 
     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
   </refsect1>
diff --git a/man/sd_journal_get_cutoff_realtime_usec.xml b/man/sd_journal_get_cutoff_realtime_usec.xml
index dc8e32bf81..b2a0634f7d 100644
--- a/man/sd_journal_get_cutoff_realtime_usec.xml
+++ b/man/sd_journal_get_cutoff_realtime_usec.xml
@@ -96,8 +96,7 @@
   <refsect1>
     <title>Notes</title>
 
-    <para>All functions listed here are thread-agnostic and only a single thread may operate
-    on a given <structname>sd_journal</structname> object.</para>
+    <xi:include href="threads-aware.xml" xpointer="strict" />
 
     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
   </refsect1>
diff --git a/man/sd_journal_get_data.xml b/man/sd_journal_get_data.xml
index 99f9500441..464fd16ace 100644
--- a/man/sd_journal_get_data.xml
+++ b/man/sd_journal_get_data.xml
@@ -156,7 +156,13 @@
     success or a negative errno-style error code.</para>
   </refsect1>
 
-  <xi:include href="libsystemd-pkgconfig.xml" />
+  <refsect1>
+    <title>Notes</title>
+
+    <xi:include href="threads-aware.xml" xpointer="strict"/>
+
+    <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
+  </refsect1>
 
   <refsect1>
     <title>Examples</title>
diff --git a/man/sd_journal_get_fd.xml b/man/sd_journal_get_fd.xml
index 7edbc4bc25..2186b685bf 100644
--- a/man/sd_journal_get_fd.xml
+++ b/man/sd_journal_get_fd.xml
@@ -226,14 +226,9 @@ else {
   <refsect1>
     <title>Notes</title>
 
-    <para>The <function>sd_journal_get_fd()</function>,
-    <function>sd_journal_get_events()</function>,
-    <function>sd_journal_reliable_fd()</function>,
-    <function>sd_journal_process()</function> and
-    <function>sd_journal_wait()</function> interfaces are available as
-    a shared library, which can be compiled and linked to with the
-    <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
-    file.</para>
+    <xi:include href="threads-aware.xml" xpointer="strict"/>
+
+    <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
   </refsect1>
 
   <refsect1>
diff --git a/man/sd_journal_get_realtime_usec.xml b/man/sd_journal_get_realtime_usec.xml
index 2030e8372d..e0f5c4d2e9 100644
--- a/man/sd_journal_get_realtime_usec.xml
+++ b/man/sd_journal_get_realtime_usec.xml
@@ -89,7 +89,13 @@
     <function>sd_journal_get_monotonic_usec()</function>.</para>
   </refsect1>
 
-  <xi:include href="libsystemd-pkgconfig.xml" />
+  <refsect1>
+    <title>Notes</title>
+
+    <xi:include href="threads-aware.xml" xpointer="strict"/>
+
+    <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
+  </refsect1>
 
   <refsect1>
     <title>See Also</title>
diff --git a/man/sd_journal_get_usage.xml b/man/sd_journal_get_usage.xml
index 358a62d066..39f53dd5eb 100644
--- a/man/sd_journal_get_usage.xml
+++ b/man/sd_journal_get_usage.xml
@@ -56,8 +56,7 @@
   <refsect1>
     <title>Notes</title>
 
-    <para>All functions listed here are thread-agnostic and only a single thread may operate
-    on a given <structname>sd_journal</structname> object.</para>
+    <xi:include href="threads-aware.xml" xpointer="strict"/>
 
     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
   </refsect1>
diff --git a/man/sd_journal_has_runtime_files.xml b/man/sd_journal_has_runtime_files.xml
index b7bbf224d4..44fdc8d186 100644
--- a/man/sd_journal_has_runtime_files.xml
+++ b/man/sd_journal_has_runtime_files.xml
@@ -66,8 +66,7 @@
   <refsect1>
     <title>Notes</title>
 
-    <para>All functions listed here are thread-agnostic and only a single thread may operate
-    on a given <structname>sd_journal</structname> object.</para>
+    <xi:include href="threads-aware.xml" xpointer="strict"/>
 
     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
   </refsect1>
diff --git a/man/sd_journal_next.xml b/man/sd_journal_next.xml
index c0ca5a8a14..9a27d1426e 100644
--- a/man/sd_journal_next.xml
+++ b/man/sd_journal_next.xml
@@ -122,8 +122,7 @@
   <refsect1>
     <title>Notes</title>
 
-    <para>All functions listed here are thread-agnostic and only a single thread may operate
-    on a given <structname>sd_journal</structname> object.</para>
+    <xi:include href="threads-aware.xml" xpointer="strict"/>
 
     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
   </refsect1>
diff --git a/man/sd_journal_open.xml b/man/sd_journal_open.xml
index 9f600b223f..cf787b7ea1 100644
--- a/man/sd_journal_open.xml
+++ b/man/sd_journal_open.xml
@@ -6,7 +6,8 @@
   SPDX-License-Identifier: LGPL-2.1+
 -->
 
-<refentry id="sd_journal_open">
+<refentry id="sd_journal_open"
+          xmlns:xi="http://www.w3.org/2001/XInclude">
 
   <refentryinfo>
     <title>sd_journal_open</title>
@@ -184,15 +185,9 @@
   <refsect1>
     <title>Notes</title>
 
-    <para>All functions listed here are thread-agnostic and only a single thread may operate
-    on a given <structname>sd_journal</structname> object.</para>
+    <xi:include href="threads-aware.xml" xpointer="strict"/>
 
-    <para>The <function>sd_journal_open()</function>,
-    <function>sd_journal_open_directory()</function> and
-    <function>sd_journal_close()</function> interfaces are available
-    as a shared library, which can be compiled and linked to with the
-    <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
-    file.</para>
+    <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
   </refsect1>
 
   <refsect1>
diff --git a/man/sd_journal_print.xml b/man/sd_journal_print.xml
index f8ff7ba093..e18cf88bbc 100644
--- a/man/sd_journal_print.xml
+++ b/man/sd_journal_print.xml
@@ -177,7 +177,8 @@ sd_journal_send("MESSAGE=Hello World, this is PID %lu!", (unsigned long) getpid(
 
   <refsect1>
     <title>Thread safety</title>
-    <para>All functions listed here are thread-safe and may be called in parallel from multiple threads.</para>
+
+    <xi:include href="threads-aware.xml" xpointer="safe"/>
 
     <para><function>sd_journal_sendv()</function> is "async signal safe" in the meaning of <citerefentry
     project='man-pages'><refentrytitle>signal-safety</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
diff --git a/man/sd_journal_query_unique.xml b/man/sd_journal_query_unique.xml
index c62f333eab..9adafa1144 100644
--- a/man/sd_journal_query_unique.xml
+++ b/man/sd_journal_query_unique.xml
@@ -126,8 +126,7 @@
   <refsect1>
     <title>Notes</title>
 
-    <para>All functions listed here are thread-agnostic and only a single thread may operate
-    on a given <structname>sd_journal</structname> object.</para>
+    <xi:include href="threads-aware.xml" xpointer="strict"/>
 
     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
   </refsect1>
diff --git a/man/sd_journal_seek_head.xml b/man/sd_journal_seek_head.xml
index 86274071f5..da88d241e8 100644
--- a/man/sd_journal_seek_head.xml
+++ b/man/sd_journal_seek_head.xml
@@ -120,8 +120,7 @@
   <refsect1>
     <title>Notes</title>
 
-    <para>All functions listed here are thread-agnostic and only a single thread may operate
-    on a given <structname>sd_journal</structname> object.</para>
+    <xi:include href="threads-aware.xml" xpointer="strict"/>
 
     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
   </refsect1>
diff --git a/man/sd_journal_stream_fd.xml b/man/sd_journal_stream_fd.xml
index de76cabb4d..8e65dc7658 100644
--- a/man/sd_journal_stream_fd.xml
+++ b/man/sd_journal_stream_fd.xml
@@ -92,8 +92,7 @@
   <refsect1>
     <title>Notes</title>
 
-    <para>Function <function>sd_journal_stream_fd()</function> is thread-safe and may be called
-    from multiple threads.</para>
+    <xi:include href="threads-aware.xml" xpointer="safe"/>
 
     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
   </refsect1>
diff --git a/man/threads-aware.xml b/man/threads-aware.xml
new file mode 100644
index 0000000000..7985f4acd1
--- /dev/null
+++ b/man/threads-aware.xml
@@ -0,0 +1,17 @@
+<?xml version="1.0"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
+
+<!--
+  SPDX-License-Identifier: LGPL-2.1+
+-->
+
+<refsect1>
+
+<para id="strict">All functions listed here are thread-agnostic and only a single specific thread may operate on a
+given object during its entire lifetime. It's safe to allocate multiple independent objects and use each from a
+specific thread in parallel. However, it's not safe to allocate such an object in one thread, and operate or free it
+from any other, even if locking is used to ensure these threads don't operate on it at the very same time.</para>
+
+<para id="safe">All functions listed here are thread-safe and may be called in parallel from multiple threads.</para>
+
+</refsect1>
diff --git a/src/basic/hashmap.c b/src/basic/hashmap.c
index 69a7d70b04..44d718c83d 100644
--- a/src/basic/hashmap.c
+++ b/src/basic/hashmap.c
@@ -6,8 +6,9 @@
 #include <string.h>
 
 #include "alloc-util.h"
-#include "hashmap.h"
+#include "env-util.h"
 #include "fileio.h"
+#include "hashmap.h"
 #include "macro.h"
 #include "mempool.h"
 #include "process-util.h"
@@ -766,20 +767,31 @@ static void reset_direct_storage(HashmapBase *h) {
         memset(p, DIB_RAW_INIT, sizeof(dib_raw_t) * hi->n_direct_buckets);
 }
 
+static bool use_pool(void) {
+        static int b = -1;
+
+        if (!is_main_thread())
+                return false;
+
+        if (b < 0)
+                b = getenv_bool("SYSTEMD_MEMPOOL") != 0;
+
+        return b;
+}
+
 static struct HashmapBase *hashmap_base_new(const struct hash_ops *hash_ops, enum HashmapType type HASHMAP_DEBUG_PARAMS) {
         HashmapBase *h;
         const struct hashmap_type_info *hi = &hashmap_type_info[type];
-        bool use_pool;
+        bool up;
 
-        use_pool = is_main_thread();
-
-        h = use_pool ? mempool_alloc0_tile(hi->mempool) : malloc0(hi->head_size);
+        up = use_pool();
 
+        h = up ? mempool_alloc0_tile(hi->mempool) : malloc0(hi->head_size);
         if (!h)
                 return NULL;
 
         h->type = type;
-        h->from_pool = use_pool;
+        h->from_pool = up;
         h->hash_ops = hash_ops ? hash_ops : &trivial_hash_ops;
 
         if (type == HASHMAP_TYPE_ORDERED) {
@@ -857,9 +869,11 @@ static void hashmap_free_no_clear(HashmapBase *h) {
         assert_se(pthread_mutex_unlock(&hashmap_debug_list_mutex) == 0);
 #endif
 
-        if (h->from_pool)
+        if (h->from_pool) {
+                /* Ensure that the object didn't get migrated between threads. */
+                assert_se(is_main_thread());
                 mempool_free_tile(hashmap_type_info[h->type].mempool, h);
-        else
+        } else
                 free(h);
 }
 
diff --git a/src/resolve/test-resolved-etc-hosts.c b/src/resolve/test-resolved-etc-hosts.c
index 5b8f1e220e..b7dba0d780 100644
--- a/src/resolve/test-resolved-etc-hosts.c
+++ b/src/resolve/test-resolved-etc-hosts.c
@@ -9,7 +9,7 @@
 static void test_parse_etc_hosts_system(void) {
         _cleanup_fclose_ FILE *f = NULL;
 
-        f = fopen("/etc/hosts", "r");
+        f = fopen("/etc/hosts", "re");
         if (!f) {
                 assert_se(errno == -ENOENT);
                 return;
@@ -27,7 +27,7 @@ static void test_parse_etc_hosts(const char *fname) {
         _cleanup_fclose_ FILE *f;
 
         if (fname) {
-                f = fopen(fname, "r");
+                f = fopen(fname, "re");
                 assert_se(f);
         } else {
                 fd = mkostemp_safe(t);