src/test/modules/delay_execution/delay_execution.c

/*-------------------------------------------------------------------------
 *
 * delay_execution.c
 *		Test module to allow delay between parsing and execution of a query.
 *
 * The delay is implemented by taking and immediately releasing a specified
 * advisory lock.  If another process has previously taken that lock, the
 * current process will be blocked until the lock is released; otherwise,
 * there's no effect.  This allows an isolationtester script to reliably
 * test behaviors where some specified action happens in another backend
 * between parsing and execution of any desired query.
 *
 * Copyright (c) 2020-2021, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *	  src/test/modules/delay_execution/delay_execution.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <limits.h>

#include "optimizer/planner.h"
#include "utils/builtins.h"
#include "utils/guc.h"
#include "utils/inval.h"


PG_MODULE_MAGIC;

/* GUC: advisory lock ID to use.  Zero disables the feature. */
static int	post_planning_lock_id = 0;

/* Save previous planner hook user to be a good citizen */
static planner_hook_type prev_planner_hook = NULL;

/* Module load/unload functions */
void		_PG_init(void);
void		_PG_fini(void);


/* planner_hook function to provide the desired delay */
static PlannedStmt *
delay_execution_planner(Query *parse, const char *query_string,
						int cursorOptions, ParamListInfo boundParams, OptimizerOptions *optimizer_options)
{
	PlannedStmt *result;

	/* Invoke the planner, possibly via a previous hook user */
	if (prev_planner_hook)
		result = prev_planner_hook(parse, query_string, cursorOptions,
								   boundParams, optimizer_options);
	else
		result = standard_planner(parse, query_string, cursorOptions,
								  boundParams, optimizer_options);

	/* If enabled, delay by taking and releasing the specified lock */
	if (post_planning_lock_id != 0)
	{
		DirectFunctionCall1(pg_advisory_lock_int8,
							Int64GetDatum((int64) post_planning_lock_id));
		DirectFunctionCall1(pg_advisory_unlock_int8,
							Int64GetDatum((int64) post_planning_lock_id));

		/*
		 * Ensure that we notice any pending invalidations, since the advisory
		 * lock functions don't do this.
		 */
		AcceptInvalidationMessages();
	}

	return result;
}

/* Module load function */
void
_PG_init(void)
{
	/* Set up the GUC to control which lock is used */
	DefineCustomIntVariable("delay_execution.post_planning_lock_id",
							"Sets the advisory lock ID to be locked/unlocked after planning.",
							"Zero disables the delay.",
							&post_planning_lock_id,
							0,
							0, INT_MAX,
							PGC_USERSET,
							0,
							NULL,
							NULL,
							NULL);

	/* Install our hook */
	prev_planner_hook = planner_hook;
	planner_hook = delay_execution_planner;
}

/* Module unload function (pro forma, not used currently) */
void
_PG_fini(void)
{
	planner_hook = prev_planner_hook;
}