Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * dsm_registry.c
4 : * Functions for interfacing with the dynamic shared memory registry.
5 : *
6 : * This provides a way for libraries to use shared memory without needing
7 : * to request it at startup time via a shmem_request_hook. The registry
8 : * stores dynamic shared memory (DSM) segment handles keyed by a
9 : * library-specified string.
10 : *
11 : * The registry is accessed by calling GetNamedDSMSegment(). If a segment
12 : * with the provided name does not yet exist, it is created and initialized
13 : * with the provided init_callback callback function. Otherwise,
14 : * GetNamedDSMSegment() simply ensures that the segment is attached to the
15 : * current backend. This function guarantees that only one backend
16 : * initializes the segment and that all other backends just attach it.
17 : *
18 : * A DSA can be created in or retrieved from the registry by calling
19 : * GetNamedDSA(). As with GetNamedDSMSegment(), if a DSA with the provided
20 : * name does not yet exist, it is created. Otherwise, GetNamedDSA()
21 : * ensures the DSA is attached to the current backend. This function
22 : * guarantees that only one backend initializes the DSA and that all other
23 : * backends just attach it.
24 : *
25 : * A dshash table can be created in or retrieved from the registry by
26 : * calling GetNamedDSHash(). As with GetNamedDSMSegment(), if a hash
27 : * table with the provided name does not yet exist, it is created.
28 : * Otherwise, GetNamedDSHash() ensures the hash table is attached to the
29 : * current backend. This function guarantees that only one backend
30 : * initializes the table and that all other backends just attach it.
31 : *
32 : * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
33 : * Portions Copyright (c) 1994, Regents of the University of California
34 : *
35 : * IDENTIFICATION
36 : * src/backend/storage/ipc/dsm_registry.c
37 : *
38 : *-------------------------------------------------------------------------
39 : */
40 :
41 : #include "postgres.h"
42 :
43 : #include "funcapi.h"
44 : #include "lib/dshash.h"
45 : #include "storage/dsm_registry.h"
46 : #include "storage/lwlock.h"
47 : #include "storage/shmem.h"
48 : #include "utils/builtins.h"
49 : #include "utils/memutils.h"
50 :
51 : typedef struct DSMRegistryCtxStruct
52 : {
53 : dsa_handle dsah;
54 : dshash_table_handle dshh;
55 : } DSMRegistryCtxStruct;
56 :
57 : static DSMRegistryCtxStruct *DSMRegistryCtx;
58 :
59 : typedef struct NamedDSMState
60 : {
61 : dsm_handle handle;
62 : size_t size;
63 : } NamedDSMState;
64 :
65 : typedef struct NamedDSAState
66 : {
67 : dsa_handle handle;
68 : int tranche;
69 : } NamedDSAState;
70 :
71 : typedef struct NamedDSHState
72 : {
73 : dsa_handle dsa_handle;
74 : dshash_table_handle dsh_handle;
75 : int tranche;
76 : } NamedDSHState;
77 :
78 : typedef enum DSMREntryType
79 : {
80 : DSMR_ENTRY_TYPE_DSM,
81 : DSMR_ENTRY_TYPE_DSA,
82 : DSMR_ENTRY_TYPE_DSH,
83 : } DSMREntryType;
84 :
85 : static const char *const DSMREntryTypeNames[] =
86 : {
87 : [DSMR_ENTRY_TYPE_DSM] = "segment",
88 : [DSMR_ENTRY_TYPE_DSA] = "area",
89 : [DSMR_ENTRY_TYPE_DSH] = "hash",
90 : };
91 :
92 : typedef struct DSMRegistryEntry
93 : {
94 : char name[NAMEDATALEN];
95 : DSMREntryType type;
96 : union
97 : {
98 : NamedDSMState dsm;
99 : NamedDSAState dsa;
100 : NamedDSHState dsh;
101 : };
102 : } DSMRegistryEntry;
103 :
104 : static const dshash_parameters dsh_params = {
105 : offsetof(DSMRegistryEntry, type),
106 : sizeof(DSMRegistryEntry),
107 : dshash_strcmp,
108 : dshash_strhash,
109 : dshash_strcpy,
110 : LWTRANCHE_DSM_REGISTRY_HASH
111 : };
112 :
113 : static dsa_area *dsm_registry_dsa;
114 : static dshash_table *dsm_registry_table;
115 :
116 : Size
117 6312 : DSMRegistryShmemSize(void)
118 : {
119 6312 : return MAXALIGN(sizeof(DSMRegistryCtxStruct));
120 : }
121 :
122 : void
123 2204 : DSMRegistryShmemInit(void)
124 : {
125 : bool found;
126 :
127 2204 : DSMRegistryCtx = (DSMRegistryCtxStruct *)
128 2204 : ShmemInitStruct("DSM Registry Data",
129 : DSMRegistryShmemSize(),
130 : &found);
131 :
132 2204 : if (!found)
133 : {
134 2204 : DSMRegistryCtx->dsah = DSA_HANDLE_INVALID;
135 2204 : DSMRegistryCtx->dshh = DSHASH_HANDLE_INVALID;
136 : }
137 2204 : }
138 :
139 : /*
140 : * Initialize or attach to the dynamic shared hash table that stores the DSM
141 : * registry entries, if not already done. This must be called before accessing
142 : * the table.
143 : */
144 : static void
145 106 : init_dsm_registry(void)
146 : {
147 : /* Quick exit if we already did this. */
148 106 : if (dsm_registry_table)
149 16 : return;
150 :
151 : /* Otherwise, use a lock to ensure only one process creates the table. */
152 90 : LWLockAcquire(DSMRegistryLock, LW_EXCLUSIVE);
153 :
154 90 : if (DSMRegistryCtx->dshh == DSHASH_HANDLE_INVALID)
155 : {
156 : /* Initialize dynamic shared hash table for registry. */
157 22 : dsm_registry_dsa = dsa_create(LWTRANCHE_DSM_REGISTRY_DSA);
158 22 : dsm_registry_table = dshash_create(dsm_registry_dsa, &dsh_params, NULL);
159 :
160 22 : dsa_pin(dsm_registry_dsa);
161 22 : dsa_pin_mapping(dsm_registry_dsa);
162 :
163 : /* Store handles in shared memory for other backends to use. */
164 22 : DSMRegistryCtx->dsah = dsa_get_handle(dsm_registry_dsa);
165 22 : DSMRegistryCtx->dshh = dshash_get_hash_table_handle(dsm_registry_table);
166 : }
167 : else
168 : {
169 : /* Attach to existing dynamic shared hash table. */
170 68 : dsm_registry_dsa = dsa_attach(DSMRegistryCtx->dsah);
171 68 : dsa_pin_mapping(dsm_registry_dsa);
172 68 : dsm_registry_table = dshash_attach(dsm_registry_dsa, &dsh_params,
173 68 : DSMRegistryCtx->dshh, NULL);
174 : }
175 :
176 90 : LWLockRelease(DSMRegistryLock);
177 : }
178 :
179 : /*
180 : * Initialize or attach a named DSM segment.
181 : *
182 : * This routine returns the address of the segment. init_callback is called to
183 : * initialize the segment when it is first created.
184 : */
185 : void *
186 94 : GetNamedDSMSegment(const char *name, size_t size,
187 : void (*init_callback) (void *ptr), bool *found)
188 : {
189 : DSMRegistryEntry *entry;
190 : MemoryContext oldcontext;
191 : void *ret;
192 : NamedDSMState *state;
193 : dsm_segment *seg;
194 :
195 : Assert(found);
196 :
197 94 : if (!name || *name == '\0')
198 0 : ereport(ERROR,
199 : (errmsg("DSM segment name cannot be empty")));
200 :
201 94 : if (strlen(name) >= offsetof(DSMRegistryEntry, type))
202 0 : ereport(ERROR,
203 : (errmsg("DSM segment name too long")));
204 :
205 94 : if (size == 0)
206 0 : ereport(ERROR,
207 : (errmsg("DSM segment size must be nonzero")));
208 :
209 : /* Be sure any local memory allocated by DSM/DSA routines is persistent. */
210 94 : oldcontext = MemoryContextSwitchTo(TopMemoryContext);
211 :
212 : /* Connect to the registry. */
213 94 : init_dsm_registry();
214 :
215 94 : entry = dshash_find_or_insert(dsm_registry_table, name, found);
216 94 : state = &entry->dsm;
217 94 : if (!(*found))
218 : {
219 22 : entry->type = DSMR_ENTRY_TYPE_DSM;
220 22 : state->handle = DSM_HANDLE_INVALID;
221 22 : state->size = size;
222 : }
223 72 : else if (entry->type != DSMR_ENTRY_TYPE_DSM)
224 0 : ereport(ERROR,
225 : (errmsg("requested DSM segment does not match type of existing entry")));
226 72 : else if (state->size != size)
227 0 : ereport(ERROR,
228 : (errmsg("requested DSM segment size does not match size of existing segment")));
229 :
230 94 : if (state->handle == DSM_HANDLE_INVALID)
231 : {
232 22 : *found = false;
233 :
234 : /* Initialize the segment. */
235 22 : seg = dsm_create(size, 0);
236 :
237 22 : if (init_callback)
238 22 : (*init_callback) (dsm_segment_address(seg));
239 :
240 22 : dsm_pin_segment(seg);
241 22 : dsm_pin_mapping(seg);
242 22 : state->handle = dsm_segment_handle(seg);
243 : }
244 : else
245 : {
246 : /* If the existing segment is not already attached, attach it now. */
247 72 : seg = dsm_find_mapping(state->handle);
248 72 : if (seg == NULL)
249 : {
250 66 : seg = dsm_attach(state->handle);
251 66 : if (seg == NULL)
252 0 : elog(ERROR, "could not map dynamic shared memory segment");
253 :
254 66 : dsm_pin_mapping(seg);
255 : }
256 : }
257 :
258 94 : ret = dsm_segment_address(seg);
259 94 : dshash_release_lock(dsm_registry_table, entry);
260 94 : MemoryContextSwitchTo(oldcontext);
261 :
262 94 : return ret;
263 : }
264 :
265 : /*
266 : * Initialize or attach a named DSA.
267 : *
268 : * This routine returns a pointer to the DSA. A new LWLock tranche ID will be
269 : * generated if needed. Note that the lock tranche will be registered with the
270 : * provided name. Also note that this should be called at most once for a
271 : * given DSA in each backend.
272 : */
273 : dsa_area *
274 4 : GetNamedDSA(const char *name, bool *found)
275 : {
276 : DSMRegistryEntry *entry;
277 : MemoryContext oldcontext;
278 : dsa_area *ret;
279 : NamedDSAState *state;
280 :
281 : Assert(found);
282 :
283 4 : if (!name || *name == '\0')
284 0 : ereport(ERROR,
285 : (errmsg("DSA name cannot be empty")));
286 :
287 4 : if (strlen(name) >= offsetof(DSMRegistryEntry, type))
288 0 : ereport(ERROR,
289 : (errmsg("DSA name too long")));
290 :
291 : /* Be sure any local memory allocated by DSM/DSA routines is persistent. */
292 4 : oldcontext = MemoryContextSwitchTo(TopMemoryContext);
293 :
294 : /* Connect to the registry. */
295 4 : init_dsm_registry();
296 :
297 4 : entry = dshash_find_or_insert(dsm_registry_table, name, found);
298 4 : state = &entry->dsa;
299 4 : if (!(*found))
300 : {
301 2 : entry->type = DSMR_ENTRY_TYPE_DSA;
302 2 : state->handle = DSA_HANDLE_INVALID;
303 2 : state->tranche = -1;
304 : }
305 2 : else if (entry->type != DSMR_ENTRY_TYPE_DSA)
306 0 : ereport(ERROR,
307 : (errmsg("requested DSA does not match type of existing entry")));
308 :
309 4 : if (state->tranche == -1)
310 : {
311 2 : *found = false;
312 :
313 : /* Initialize the LWLock tranche for the DSA. */
314 2 : state->tranche = LWLockNewTrancheId(name);
315 : }
316 :
317 4 : if (state->handle == DSA_HANDLE_INVALID)
318 : {
319 2 : *found = false;
320 :
321 : /* Initialize the DSA. */
322 2 : ret = dsa_create(state->tranche);
323 2 : dsa_pin(ret);
324 2 : dsa_pin_mapping(ret);
325 :
326 : /* Store handle for other backends to use. */
327 2 : state->handle = dsa_get_handle(ret);
328 : }
329 2 : else if (dsa_is_attached(state->handle))
330 0 : ereport(ERROR,
331 : (errmsg("requested DSA already attached to current process")));
332 : else
333 : {
334 : /* Attach to existing DSA. */
335 2 : ret = dsa_attach(state->handle);
336 2 : dsa_pin_mapping(ret);
337 : }
338 :
339 4 : dshash_release_lock(dsm_registry_table, entry);
340 4 : MemoryContextSwitchTo(oldcontext);
341 :
342 4 : return ret;
343 : }
344 :
345 : /*
346 : * Initialize or attach a named dshash table.
347 : *
348 : * This routine returns the address of the table. The tranche_id member of
349 : * params is ignored; a new LWLock tranche ID will be generated if needed.
350 : * Note that the lock tranche will be registered with the provided name. Also
351 : * note that this should be called at most once for a given table in each
352 : * backend.
353 : */
354 : dshash_table *
355 4 : GetNamedDSHash(const char *name, const dshash_parameters *params, bool *found)
356 : {
357 : DSMRegistryEntry *entry;
358 : MemoryContext oldcontext;
359 : dshash_table *ret;
360 : NamedDSHState *dsh_state;
361 :
362 : Assert(params);
363 : Assert(found);
364 :
365 4 : if (!name || *name == '\0')
366 0 : ereport(ERROR,
367 : (errmsg("DSHash name cannot be empty")));
368 :
369 4 : if (strlen(name) >= offsetof(DSMRegistryEntry, type))
370 0 : ereport(ERROR,
371 : (errmsg("DSHash name too long")));
372 :
373 : /* Be sure any local memory allocated by DSM/DSA routines is persistent. */
374 4 : oldcontext = MemoryContextSwitchTo(TopMemoryContext);
375 :
376 : /* Connect to the registry. */
377 4 : init_dsm_registry();
378 :
379 4 : entry = dshash_find_or_insert(dsm_registry_table, name, found);
380 4 : dsh_state = &entry->dsh;
381 4 : if (!(*found))
382 : {
383 2 : entry->type = DSMR_ENTRY_TYPE_DSH;
384 2 : dsh_state->dsa_handle = DSA_HANDLE_INVALID;
385 2 : dsh_state->dsh_handle = DSHASH_HANDLE_INVALID;
386 2 : dsh_state->tranche = -1;
387 : }
388 2 : else if (entry->type != DSMR_ENTRY_TYPE_DSH)
389 0 : ereport(ERROR,
390 : (errmsg("requested DSHash does not match type of existing entry")));
391 :
392 4 : if (dsh_state->tranche == -1)
393 : {
394 2 : *found = false;
395 :
396 : /* Initialize the LWLock tranche for the hash table. */
397 2 : dsh_state->tranche = LWLockNewTrancheId(name);
398 : }
399 :
400 4 : if (dsh_state->dsa_handle == DSA_HANDLE_INVALID)
401 : {
402 : dshash_parameters params_copy;
403 : dsa_area *dsa;
404 :
405 2 : *found = false;
406 :
407 : /* Initialize the DSA for the hash table. */
408 2 : dsa = dsa_create(dsh_state->tranche);
409 :
410 : /* Initialize the dshash table. */
411 2 : memcpy(¶ms_copy, params, sizeof(dshash_parameters));
412 2 : params_copy.tranche_id = dsh_state->tranche;
413 2 : ret = dshash_create(dsa, ¶ms_copy, NULL);
414 :
415 2 : dsa_pin(dsa);
416 2 : dsa_pin_mapping(dsa);
417 :
418 : /* Store handles for other backends to use. */
419 2 : dsh_state->dsa_handle = dsa_get_handle(dsa);
420 2 : dsh_state->dsh_handle = dshash_get_hash_table_handle(ret);
421 : }
422 2 : else if (dsa_is_attached(dsh_state->dsa_handle))
423 0 : ereport(ERROR,
424 : (errmsg("requested DSHash already attached to current process")));
425 : else
426 : {
427 : dsa_area *dsa;
428 :
429 : /* XXX: Should we verify params matches what table was created with? */
430 :
431 : /* Attach to existing DSA for the hash table. */
432 2 : dsa = dsa_attach(dsh_state->dsa_handle);
433 2 : dsa_pin_mapping(dsa);
434 :
435 : /* Attach to existing dshash table. */
436 2 : ret = dshash_attach(dsa, params, dsh_state->dsh_handle, NULL);
437 : }
438 :
439 4 : dshash_release_lock(dsm_registry_table, entry);
440 4 : MemoryContextSwitchTo(oldcontext);
441 :
442 4 : return ret;
443 : }
444 :
445 : Datum
446 4 : pg_get_dsm_registry_allocations(PG_FUNCTION_ARGS)
447 : {
448 4 : ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
449 : DSMRegistryEntry *entry;
450 : MemoryContext oldcontext;
451 : dshash_seq_status status;
452 :
453 4 : InitMaterializedSRF(fcinfo, MAT_SRF_USE_EXPECTED_DESC);
454 :
455 : /* Be sure any local memory allocated by DSM/DSA routines is persistent. */
456 4 : oldcontext = MemoryContextSwitchTo(TopMemoryContext);
457 4 : init_dsm_registry();
458 4 : MemoryContextSwitchTo(oldcontext);
459 :
460 4 : dshash_seq_init(&status, dsm_registry_table, false);
461 10 : while ((entry = dshash_seq_next(&status)) != NULL)
462 : {
463 : Datum vals[3];
464 6 : bool nulls[3] = {0};
465 :
466 : /* Do not show partially-initialized entries. */
467 6 : if (entry->type == DSMR_ENTRY_TYPE_DSM &&
468 2 : entry->dsm.handle == DSM_HANDLE_INVALID)
469 0 : continue;
470 6 : if (entry->type == DSMR_ENTRY_TYPE_DSA &&
471 2 : entry->dsa.handle == DSA_HANDLE_INVALID)
472 0 : continue;
473 6 : if (entry->type == DSMR_ENTRY_TYPE_DSH &&
474 2 : entry->dsh.dsa_handle == DSA_HANDLE_INVALID)
475 0 : continue;
476 :
477 6 : vals[0] = CStringGetTextDatum(entry->name);
478 6 : vals[1] = CStringGetTextDatum(DSMREntryTypeNames[entry->type]);
479 :
480 : /*
481 : * Since we can't know the size of DSA/dshash entries without first
482 : * attaching to them, return NULL for those.
483 : */
484 6 : if (entry->type == DSMR_ENTRY_TYPE_DSM)
485 2 : vals[2] = Int64GetDatum(entry->dsm.size);
486 : else
487 4 : nulls[2] = true;
488 :
489 6 : tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, vals, nulls);
490 : }
491 4 : dshash_seq_term(&status);
492 :
493 4 : return (Datum) 0;
494 : }
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