provsql_shmem.c File Reference

Shared-memory segment lifecycle and LWLock management. More...

#include <unistd.h>
#include "postgres.h"
#include "storage/shmem.h"
#include "provsql_shmem.h"
#include "provsql_mmap.h"

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Functions
void	provsql_shmem_startup (void)
	Initialise the ProvSQL shared-memory segment.
Size	provsql_memsize (void)
	Return the number of bytes required for the shared-memory segment.
void	provsql_shmem_request (void)
	Request shared memory from PostgreSQL (PG ≥ 15).
void	provsql_shmem_lock_exclusive (void)
	Acquire the ProvSQL LWLock in exclusive mode.
void	provsql_shmem_lock_shared (void)
	Acquire the ProvSQL LWLock in shared mode.
void	provsql_shmem_unlock (void)
	Release the ProvSQL LWLock.

Variables
shmem_startup_hook_type	prev_shmem_startup = NULL
	Saved pointer to the previous shmem_startup_hook, for chaining.
provsqlSharedState *	provsql_shared_state = NULL
	Pointer to the ProvSQL shared-memory segment (set in provsql_shmem_startup).

Detailed Description

Shared-memory segment lifecycle and LWLock management.

Implements the functions declared in provsql_shmem.h:

• provsql_shmem_startup(): allocates (or attaches to) the provsqlSharedState segment, initialises the LWLock, and calls pipe(2) to create the two inter-process pipes. Chains to prev_shmem_startup if set.
• provsql_memsize(): returns the size of the shared segment.
• provsql_shmem_request(): requests shared memory on PG ≥ 15.
• provsql_shmem_lock_exclusive() / provsql_shmem_lock_shared() / provsql_shmem_unlock(): thin wrappers around LWLockAcquire() / LWLockRelease().

Definition in file provsql_shmem.c.

Function Documentation

provsql_memsize()

Size provsql_memsize

(

void

)

Return the number of bytes required for the shared-memory segment.

Used by PostgreSQL's shared-memory allocator during startup.

Returns

Size in bytes of the provsqlSharedState structure.

Definition at line 69 of file provsql_shmem.c.

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provsql_shmem_lock_exclusive()

void provsql_shmem_lock_exclusive

(

void

)

Acquire the ProvSQL LWLock in exclusive mode.

Callers must pair this with provsql_shmem_unlock().

Definition at line 86 of file provsql_shmem.c.

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provsql_shmem_lock_shared()

void provsql_shmem_lock_shared

(

void

)

Acquire the ProvSQL LWLock in shared mode.

Multiple backends may hold the shared lock simultaneously. Callers must pair this with provsql_shmem_unlock().

Definition at line 91 of file provsql_shmem.c.

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provsql_shmem_request()

void provsql_shmem_request

(

void

)

Request shared memory from PostgreSQL (PG ≥ 15).

Called from the shmem_request_hook (introduced in PostgreSQL 15) to reserve the segment before shared memory is finalised. Chains to prev_shmem_request if set. On older PostgreSQL versions this is a no-op because memory reservation happened in _PG_init().

Definition at line 74 of file provsql_shmem.c.

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provsql_shmem_startup()

void provsql_shmem_startup

(

void

)

Initialise the ProvSQL shared-memory segment.

Called from the shmem_startup_hook. Creates (or attaches to) the provsqlSharedState segment and initialises the embedded LWLock and pipe file descriptors. Chains to prev_shmem_startup if set.

Definition at line 31 of file provsql_shmem.c.

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provsql_shmem_unlock()

void provsql_shmem_unlock

(

void

)

Release the ProvSQL LWLock.

Must be called after provsql_shmem_lock_exclusive() or provsql_shmem_lock_shared().

Definition at line 96 of file provsql_shmem.c.

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Variable Documentation

prev_shmem_startup

shmem_startup_hook_type prev_shmem_startup = NULL

Saved pointer to the previous shmem_startup_hook, for chaining.

Definition at line 24 of file provsql_shmem.c.

provsql_shared_state

provsqlSharedState* provsql_shared_state = NULL

Pointer to the ProvSQL shared-memory segment (set in provsql_shmem_startup).

Definition at line 29 of file provsql_shmem.c.