[SQLite] Hack to touch page cache to debug slow connection close.

third_party/sqlite/amalgamation/sqlite3.c

Index: third_party/sqlite/amalgamation/sqlite3.c
diff --git a/third_party/sqlite/amalgamation/sqlite3.c b/third_party/sqlite/amalgamation/sqlite3.c
index 9c66c16c9e47cab0198735fcac01648a2c6be556..f82ed1cb45dc0527bb0595a1b448ae7c1aec780e 100644
--- a/third_party/sqlite/amalgamation/sqlite3.c
+++ b/third_party/sqlite/amalgamation/sqlite3.c
@@ -126259,3 +126259,94 @@ SQLITE_PRIVATE void sqlite3Fts3IcuTokenizerModule(
 #endif /* !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS3) */
 
 /************** End of fts3_icu.c ********************************************/
+
+/* Touch the bigs of pCache which will be processed by
+** pcache1TruncateUnsafe(), pcache1FreePage(), and pcache1Free()
+** during sqlite3_close().  *pnTouched will have the number of bytes
+** represented by the pages touched added to it. */
+SQLITE_PRIVATE void pcache1VisitUnsafe(PCache1 *pCache,
+                                       unsigned int *pnTouched){
+  unsigned int iHash;
+
+  assert( sqlite3_mutex_held(pCache->pGroup->mutex) );
+
+  for(iHash=0; iHash<pCache->nHash; iHash++){
+    PgHdr1 *pp = pCache->apHash[iHash];
+    PgHdr1 *lp = pp;
+    unsigned int s = 0;
+    while (pp) {
+      /* Crash if a loop is detected. */
+      /* NOTE(shess): Touches the PgHdr1 structure as a side effect.
+      ** If this check is removed, revise the code to match ordering
+      ** in pcache1TruncateUnsafe().  Yes, I realize this is
+      ** probably reordered to heck and back.
+      */
+      if (lp == pp->pNext) {
+        int *zero = NULL;
+        *zero = 42;
+      }
+
+      /* Touch the data area, in case it's on a prior VM page. */
+      *pnTouched += sqlite3MallocSize(PGHDR1_TO_PAGE(pp));
+
+      pp = pp->pNext;
+
+      /* Bump the loop-detection pointer forward every time s is an
+      ** even power of 2. */
+      s++;
+      if (!(s & (s-1))) {
+        lp = pp;
+      }
+    }
+  }
+}
+
+/* TODO(shess): Debugging code for http://crbug.com/95527 .
+** Touch the entire page cache for the given db.  The idea is that if
+** paging activity is causing the slowdown, the shutdown monitor will
+** see things happening here, rather than in sqlite3_close().
+*/
+int sqlite3_95527(sqlite3 *db, unsigned int *pnTouched){
+  unsigned int iDb;
+
+  /* This code assumes that pcache1 is the pager cache implementation. */
+  if (sqlite3GlobalConfig.pcache.xTruncate != pcache1Truncate) {
+    return SQLITE_OK;
+  }
+
+  /* This setup is like sqlite3_close(). */
+  if( !db ){
+    return SQLITE_OK;
+  }
+  if( !sqlite3SafetyCheckSickOrOk(db) ){
+    return SQLITE_MISUSE_BKPT;
+  }
+  sqlite3_mutex_enter(db->mutex);
+
+  /* A sqlite3* connection may refer to multiple underlying database
+     files.  Usually these will be 'main' and 'temp', with 'temp' having
+     no btree or pager. */
+  for(iDb=0; iDb<db->nDb; iDb++){
+    Btree *b;
+    Pager *p;
+    PCache1 *pCache;
+    struct Db *pDb = &db->aDb[iDb];
+    if (!pDb) continue;
+
+    b = pDb->pBt;
+    if (!b) continue;
+
+    p = sqlite3BtreePager(b);
+    if (!p) continue;
+
+    pCache = (PCache1*)p->pPCache->pCache;
+    if (!pCache) continue;
+
+    pcache1EnterMutex(pCache->pGroup);
+    pcache1VisitUnsafe(pCache, pnTouched);
+    pcache1LeaveMutex(pCache->pGroup);
+  }
+
+  sqlite3_mutex_leave(db->mutex);
+  return SQLITE_OK;
+}