Movatterモバイル変換

[0]ホーム
URL:

Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly

 Sign up
Appearance settings

Commitfe705ef

Browse files
committed
doc: Expand section related to LWLocks and shared memory
The documentation includes a section describing how to define customLWLocks in extensions using the shmem hooks. However, it has nevermentioned the second, more flexible method based on the followingroutines:- LWLockNewTrancheId() to allocate a tranche ID.- LWLockRegisterTranche() to associate a name to a tranche ID.- LWLockInitialize() to initialize a LWLock with a tranche ID.autoprewarm.c is the only example of extension in the tree thatallocates a LWLock this way.This commit adds some documentation about all that. While on it, acomment is added about the need of AddinShmemInitLock. This is requiredespecially for EXEC_BACKEND builds (aka Windows, normally), as per aremark from Alexander, because backends can execute shmem initializationpaths concurrently.Author: Aleksander Alekseev, Michael PaquierDiscussion:https://postgr.es/m/CAJ7c6TPKhFgL+54cdTD9yGpG4+sNcyJ+N1GvQqAxgWENAOa3VA@mail.gmail.com
1 parent6ec62b7 commitfe705ef

File tree

1 file changed

+30
-0
lines changed

1 file changed

+30
-0
lines changed

‎doc/src/sgml/xfunc.sgml‎

Lines changed: 30 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3428,6 +3428,29 @@ void RequestNamedLWLockTranche(const char *tranche_name, int num_lwlocks)
34283428
<filename>contrib/pg_stat_statements/pg_stat_statements.c</filename> in the
34293429
<productname>PostgreSQL</productname> source tree.
34303430
</para>
3431+
<para>
3432+
There is another, more flexible method of obtaining LWLocks. First,
3433+
allocate a <literal>tranche_id</literal> from a shared counter by
3434+
calling:
3435+
<programlisting>
3436+
int LWLockNewTrancheId(void)
3437+
</programlisting>
3438+
Next, each individual process using the <literal>tranche_id</literal>
3439+
should associate it with a <literal>tranche_name</literal> by calling:
3440+
<programlisting>
3441+
void LWLockRegisterTranche(int tranche_id, const char *tranche_name)
3442+
</programlisting>
3443+
It is also required to call <function>LWLockInitialize</function> once
3444+
per LWLock, passing the <literal>tranche_id</literal> as argument:
3445+
<programlisting>
3446+
void LWLockInitialize(LWLock *lock, int tranche_id)
3447+
</programlisting>
3448+
A complete usage example of <function>LWLockNewTrancheId</function>,
3449+
<function>LWLockInitialize</function> and
3450+
<function>LWLockRegisterTranche</function> can be found in
3451+
<filename>contrib/pg_prewarm/autoprewarm.c</filename> in the
3452+
<productname>PostgreSQL</productname> source tree.
3453+
</para>
34313454
<para>
34323455
To avoid possible race-conditions, each backend should use the LWLock
34333456
<function>AddinShmemInitLock</function> when connecting to and initializing
@@ -3451,6 +3474,13 @@ if (!ptr)
34513474
}
34523475
</programlisting>
34533476
</para>
3477+
<para>
3478+
It is convenient to use <literal>shmem_startup_hook</literal> which allows
3479+
placing all the code responsible for initializing shared memory in one
3480+
place. When using <literal>shmem_startup_hook</literal> the extension
3481+
still needs to acquire <function>AddinShmemInitLock</function> in order to
3482+
work properly on all the supported platforms.
3483+
</para>
34543484
</sect2>
34553485

34563486
<sect2 id="xfunc-addin-wait-events">

0 commit comments

Comments
 (0)
[8]ページ先頭
©2009-2025 Movatter.jp