Horton

Re: Proposal: Add a callback data parameter to GetNamedDSMSegment

Sami Imseih <samimseih@gmail.com>

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From: Sami Imseih <samimseih@gmail.com>
To: Zsolt Parragi <zsolt.parragi@percona.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2025-12-04T16:30:38Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Allow passing a pointer to GetNamedDSMSegment()'s init callback.

  2. Move dynamically-allocated LWLock tranche names to shared memory.

> struct Foo {
>     LWLock lock;
>     size_t size;
>     Bar data[];
> };
>
> * To create a few of these, I have to provide a lock name to the
> callback, that's the "reusing the same callback" part again
> * And then there's the question of initialization. Either I leave it
> to the caller after returning from GetNamedDSHash using the lock,

"caller after returning from GetNamedDSHash" <- do you mean
GetNamedDSMSegment ?

> or somehow I have to tell the initialization callback the array size -
> even if I can calculate the size based on a GUC,

```
typedef struct Bar {
int f1;
int f2;
} Bar;

typedef struct Foo {
LWLock lock;
size_t size;
Bar data[];
} Foo;

foo_state = GetNamedDSMSegment("Foo",

offsetof(Foo, data) + BAR_ARRAY_SIZE * sizeof(int),
                                                            foo_init_state,
                                                            &found);
```

wouldn't the above be sufficient to create a DSM segment containing
a flexible array?

--
Sami Imseih
Amazon Web Services (AWS)