Fix obsolete comment. No changes to code.

FossilOrigin-Name: 0ff59edbbba6211c98f1025018c0f7405cc6367bec3ebe2e9874f22f0f7c48ba

manifest

@@ -1,5 +1,5 @@
-C Abort\sthe\swindow\sfunction\stree\srewrite\searly\sfollowing\san\sOOM.
-D 2019-11-23T16:34:40.792
+C Fix\sobsolete\scomment.\s\sNo\schanges\sto\scode.
+D 2019-11-27T12:03:24.078
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -510,7 +510,7 @@ F src/os.c 669cc3839cc35d20f81faf0be1ab6d4581cea35e9d8f3a9d48a98d6571f7c285
 F src/os.h 48388821692e87da174ea198bf96b1b2d9d83be5dfc908f673ee21fafbe0d432
 F src/os_common.h b2f4707a603e36811d9b1a13278bffd757857b85
 F src/os_setup.h 0dbaea40a7d36bf311613d31342e0b99e2536586
-F src/os_unix.c 3e0e519f27683083a465e948e056759a8340728c222b5c394a135e0c57c220bc
+F src/os_unix.c 112995da72acac11ad335489acbbf7df097df5b496602e6ae5e08b9ed20d06ed
 F src/os_win.c 035a813cbd17f355bdcad7ab894af214a9c13a1db8aeac902365350b98cd45a7
 F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
 F src/pager.c 30f20d2263d3717f41a0d9a40f7a3d0f48ce1cfab461b875c6187ead9d6ad1c7
@@ -527,8 +527,8 @@ F src/random.c 80f5d666f23feb3e6665a6ce04c7197212a88384
 F src/resolve.c 2f8fb48e61d0006031df27e53810b6767972526d768d3cc6888435dc350c4c7a
 F src/rowset.c d977b011993aaea002cab3e0bb2ce50cf346000dff94e944d547b989f4b1fe93
 F src/select.c f403b7bd2304d4dfd5ad2614cc0ad3386a97af707922882bdabba4c14ce12975
-F src/shell.c.in 4a3a9e1c11847b1904f2b01d087af1c052f660902755abab457cab1756817ded
-F src/sqlite.h.in 4fe42f27a7be44586bbd94f49f2b097ef8a1053c747d82f135456c7f5381c85a
+F src/shell.c.in 6ecf8033fccb57b47a86e2bb87b1918f1aa5602f74bb72b1ae8c8ad1f44d2f27
+F src/sqlite.h.in d4fd966968f89426afa3924398896748a3cd82e07e0eef70e87b4aca5002b2c2
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
 F src/sqlite3ext.h 72af51aa4e912e14cd495fb6e7fac65f0940db80ed950d90911aff292cc47ce2
 F src/sqliteInt.h 98bc9562acfc361e34182aa25b00e2c73095732ddd3ba4158f984b94f5601f96
@@ -609,7 +609,7 @@ F src/vdbesort.c a3be032cc3fee0e3af31773af4a7a6f931b7230a34f53282ccf1d9a2a72343b
 F src/vdbetrace.c fa3bf238002f0bbbdfb66cc8afb0cea284ff9f148d6439bc1f6f2b4c3b7143f0
 F src/vtab.c 108f79166d4a232a8bfb9d46e2fbec191f83a87fe97f7b93fc4de976c3fa3434
 F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
-F src/wal.c bbd6838bd79c0a32144d482fb0b6a9d2d1a252fb3b16d5005ec30f2f80413b0d
+F src/wal.c 8ed0ca18d8d2728ba70a7b032723ef551cfc7fd66662863982e0c2cbfe8ac49e
 F src/wal.h 606292549f5a7be50b6227bd685fa76e3a4affad71bb8ac5ce4cb5c79f6a176a
 F src/walker.c a137468bf36c92e64d2275caa80c83902e3a0fc59273591b96c6416d3253d05d
 F src/where.c 874845fb5d93b3bc07123df8fee805e9650bd091e3ed62988273c7e2141ab8bd
@@ -1851,7 +1851,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 57070c68bbe15fc1d19a765182432e844c082909bdbc63b58fd86b96e2c521dd
-R 5ec4b862f5e315c01dbee90c995a71d6
+P 12b8fa233697f9f4026eb14fb7454c180f61aa639b1834ccdc8dcfde4420d3a4
+R a828043821ecae3894d05a23137b4c66
 U drh
-Z b069a61ef07a50420fc34a99d1dc8940
+Z f102e313d0cbfb7ab84dcd298e39c778

manifest.uuid

@@ -1 +1 @@
-d66f95a51530259ab48f78c9f91acc38055caf338b6fee846b99a8c077466e95
+0ff59edbbba6211c98f1025018c0f7405cc6367bec3ebe2e9874f22f0f7c48ba

src/os_unix.c

@@ -271,6 +271,77 @@ struct unixFile {
 #endif
 };
 
+
+/*
+** Object used to represent an shared memory buffer.  
+**
+** When multiple threads all reference the same wal-index, each thread
+** has its own unixShm object, but they all point to a single instance
+** of this unixShmNode object.  In other words, each wal-index is opened
+** only once per process.
+**
+** Each unixShmNode object is connected to a single unixInodeInfo object.
+** We could coalesce this object into unixInodeInfo, but that would mean
+** every open file that does not use shared memory (in other words, most
+** open files) would have to carry around this extra information.  So
+** the unixInodeInfo object contains a pointer to this unixShmNode object
+** and the unixShmNode object is created only when needed.
+**
+** unixMutexHeld() must be true when creating or destroying
+** this object or while reading or writing the following fields:
+**
+**      nRef
+**
+** The following fields are read-only after the object is created:
+** 
+**      hShm
+**      zFilename
+**
+** Either unixShmNode.pShmMutex must be held or unixShmNode.nRef==0 and
+** unixMutexHeld() is true when reading or writing any other field
+** in this structure.
+*/
+struct unixShmNode {
+  unixInodeInfo *pInode;     /* unixInodeInfo that owns this SHM node */
+  sqlite3_mutex *pShmMutex;  /* Mutex to access this object */
+  char *zFilename;           /* Name of the mmapped file */
+  int hShm;                  /* Open file descriptor */
+  int szRegion;              /* Size of shared-memory regions */
+  u16 nRegion;               /* Size of array apRegion */
+  u8 isReadonly;             /* True if read-only */
+  u8 isUnlocked;             /* True if no DMS lock held */
+  char **apRegion;           /* Array of mapped shared-memory regions */
+  int nRef;                  /* Number of unixShm objects pointing to this */
+  unixShm *pFirst;           /* All unixShm objects pointing to this */
+#ifdef SQLITE_DEBUG
+  u8 exclMask;               /* Mask of exclusive locks held */
+  u8 sharedMask;             /* Mask of shared locks held */
+  u8 nextShmId;              /* Next available unixShm.id value */
+#endif
+};
+
+/*
+** Structure used internally by this VFS to record the state of an
+** open shared memory connection.
+**
+** The following fields are initialized when this object is created and
+** are read-only thereafter:
+**
+**    unixShm.pShmNode
+**    unixShm.id
+**
+** All other fields are read/write.  The unixShm.pShmNode->pShmMutex must
+** be held while accessing any read/write fields.
+*/
+struct unixShm {
+  unixShmNode *pShmNode;     /* The underlying unixShmNode object */
+  unixShm *pNext;            /* Next unixShm with the same unixShmNode */
+  u8 hasMutex;               /* True if holding the unixShmNode->pShmMutex */
+  u8 id;                     /* Id of this connection within its unixShmNode */
+  u16 sharedMask;            /* Mask of shared locks held */
+  u16 exclMask;              /* Mask of exclusive locks held */
+};
+
 /* This variable holds the process id (pid) from when the xRandomness()
 ** method was called.  If xOpen() is called from a different process id,
 ** indicating that a fork() has occurred, the PRNG will be reset.
@@ -292,6 +363,7 @@ static pid_t randomnessPid = 0;
 #define UNIXFILE_DELETE      0x20     /* Delete on close */
 #define UNIXFILE_URI         0x40     /* Filename might have query parameters */
 #define UNIXFILE_NOLOCK      0x80     /* Do no file locking */
+#define UNIXFILE_REUSESHM   0x100     /* Reuse existing -shm file */
 
 /*
 ** Include code that is common to all os_*.c files
@@ -4042,6 +4114,33 @@ static int unixFileControl(sqlite3_file *id, int op, void *pArg){
       return proxyFileControl(id,op,pArg);
     }
 #endif /* SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__) */
+    case SQLITE_FCNTL_REUSE_SHM: {
+      /* Set the UNIXFILE_REUSESHM file.  If this flag is set before
+      ** the database file is first read, and the database is in WAL-mode,
+      ** and this is the first connection to connect to the database, and
+      ** there exists a -shm file from some prior connection that terminated
+      ** asynchronous, then this connection will attempt to reuse the existing
+      ** -shm file.  The default behavior (without this flag) is to scan
+      ** the entire -wal file and reconstruct the -shm file from scratch.
+      ** The default behavior is safer.  But some embedded systems want the
+      ** option to live dangerously. */
+      pFile->ctrlFlags |= UNIXFILE_REUSESHM;
+      return SQLITE_OK;
+    }
+    case SQLITE_FCNTL_SHM_HANDLE: {
+      /* If this database connection has a -shm file open, then set
+      ** *pArg to the file descriptor for that file.  If the -shm file is
+      ** not open for any reason (not opened yet, not in WAL mode, uses
+      ** an in-memory -shm file, etc) then set *pArg to -1. */
+      unixShm *pShm = pFile->pShm;
+      int h = -1;
+      if( pShm ){
+        unixShmNode *pNode = pShm->pShmNode;
+        if( pNode ) h = pNode->hShm;
+      }
+      *(int*)pArg = h;
+      return SQLITE_OK;
+    }
   }
   return SQLITE_NOTFOUND;
 }
@@ -4210,76 +4309,6 @@ static int unixGetpagesize(void){
 
 #ifndef SQLITE_OMIT_WAL
 
-/*
-** Object used to represent an shared memory buffer.  
-**
-** When multiple threads all reference the same wal-index, each thread
-** has its own unixShm object, but they all point to a single instance
-** of this unixShmNode object.  In other words, each wal-index is opened
-** only once per process.
-**
-** Each unixShmNode object is connected to a single unixInodeInfo object.
-** We could coalesce this object into unixInodeInfo, but that would mean
-** every open file that does not use shared memory (in other words, most
-** open files) would have to carry around this extra information.  So
-** the unixInodeInfo object contains a pointer to this unixShmNode object
-** and the unixShmNode object is created only when needed.
-**
-** unixMutexHeld() must be true when creating or destroying
-** this object or while reading or writing the following fields:
-**
-**      nRef
-**
-** The following fields are read-only after the object is created:
-** 
-**      hShm
-**      zFilename
-**
-** Either unixShmNode.pShmMutex must be held or unixShmNode.nRef==0 and
-** unixMutexHeld() is true when reading or writing any other field
-** in this structure.
-*/
-struct unixShmNode {
-  unixInodeInfo *pInode;     /* unixInodeInfo that owns this SHM node */
-  sqlite3_mutex *pShmMutex;  /* Mutex to access this object */
-  char *zFilename;           /* Name of the mmapped file */
-  int hShm;                  /* Open file descriptor */
-  int szRegion;              /* Size of shared-memory regions */
-  u16 nRegion;               /* Size of array apRegion */
-  u8 isReadonly;             /* True if read-only */
-  u8 isUnlocked;             /* True if no DMS lock held */
-  char **apRegion;           /* Array of mapped shared-memory regions */
-  int nRef;                  /* Number of unixShm objects pointing to this */
-  unixShm *pFirst;           /* All unixShm objects pointing to this */
-#ifdef SQLITE_DEBUG
-  u8 exclMask;               /* Mask of exclusive locks held */
-  u8 sharedMask;             /* Mask of shared locks held */
-  u8 nextShmId;              /* Next available unixShm.id value */
-#endif
-};
-
-/*
-** Structure used internally by this VFS to record the state of an
-** open shared memory connection.
-**
-** The following fields are initialized when this object is created and
-** are read-only thereafter:
-**
-**    unixShm.pShmNode
-**    unixShm.id
-**
-** All other fields are read/write.  The unixShm.pShmNode->pShmMutex must
-** be held while accessing any read/write fields.
-*/
-struct unixShm {
-  unixShmNode *pShmNode;     /* The underlying unixShmNode object */
-  unixShm *pNext;            /* Next unixShm with the same unixShmNode */
-  u8 hasMutex;               /* True if holding the unixShmNode->pShmMutex */
-  u8 id;                     /* Id of this connection within its unixShmNode */
-  u16 sharedMask;            /* Mask of shared locks held */
-  u16 exclMask;              /* Mask of exclusive locks held */
-};
-
 /*
 ** Constants used for locking
 */
@@ -4457,8 +4486,12 @@ static int unixLockSharedMemory(unixFile *pDbFd, unixShmNode *pShmNode){
       ** -shm header size) rather than 0 as a system debugging aid, to
       ** help detect if a -shm file truncation is legitimate or is the work
       ** or a rogue process. */
-      if( rc==SQLITE_OK && robust_ftruncate(pShmNode->hShm, 3) ){
-        rc = unixLogError(SQLITE_IOERR_SHMOPEN,"ftruncate",pShmNode->zFilename);
+      if( rc==SQLITE_OK
+       && (pDbFd->ctrlFlags & UNIXFILE_REUSESHM)==0
+       && robust_ftruncate(pShmNode->hShm, 3)
+      ){
+        rc = unixLogError(SQLITE_IOERR_SHMOPEN,"ftruncate",
+                          pShmNode->zFilename);
       }
     }
   }else if( lock.l_type==F_WRLCK ){

src/shell.c.in

@@ -7386,6 +7386,8 @@ static int do_meta_command(char *zLine, ShellState *p){
       { "tempfilename",   SQLITE_FCNTL_TEMPFILENAME,    ""               },
       { "has_moved",      SQLITE_FCNTL_HAS_MOVED,       ""               },  
       { "lock_timeout",   SQLITE_FCNTL_LOCK_TIMEOUT,    "MILLISEC"       },
+      { "reuse_shm",      SQLITE_FCNTL_REUSE_SHM,       ""               },
+      { "shm_handle",     SQLITE_FCNTL_SHM_HANDLE,      ""               },
     };
     int filectrl = -1;
     int iCtrl = -1;
@@ -7480,6 +7482,18 @@ static int do_meta_command(char *zLine, ShellState *p){
           isOk = 2;
           break;
         }
+        case SQLITE_FCNTL_REUSE_SHM: {
+          sqlite3_file_control(p->db, 0, filectrl, 0);
+          isOk = 2;
+          break;
+        }
+        case SQLITE_FCNTL_SHM_HANDLE: {
+          int h = -2;
+          sqlite3_file_control(p->db, 0, filectrl, &h);
+          isOk = 1;
+          iRes = h;
+          break;
+        }
       }
     }
     if( isOk==0 && iCtrl>=0 ){

src/sqlite.h.in

@@ -1147,6 +1147,8 @@ struct sqlite3_io_methods {
 #define SQLITE_FCNTL_LOCK_TIMEOUT           34
 #define SQLITE_FCNTL_DATA_VERSION           35
 #define SQLITE_FCNTL_SIZE_LIMIT             36
+#define SQLITE_FCNTL_REUSE_SHM              37
+#define SQLITE_FCNTL_SHM_HANDLE             38
 
 /* deprecated names */
 #define SQLITE_GET_LOCKPROXYFILE      SQLITE_FCNTL_GET_LOCKPROXYFILE

src/wal.c

@@ -3412,8 +3412,10 @@ int sqlite3WalFrames(
 
     /* Check if this page has already been written into the wal file by
     ** the current transaction. If so, overwrite the existing frame and
-    ** set Wal.writeLock to WAL_WRITELOCK_RECKSUM - indicating that 
-    ** checksums must be recomputed when the transaction is committed.  */
+    ** make sure pWal->iReCksum is set to the frame being overwritten or
+    ** or some earlier frame, so that we will know that checksums must
+    ** be recomputed when the transaction commits, and where to start
+    ** recomputing the checksums. */
     if( iFirst && (p->pDirty || isCommit==0) ){
       u32 iWrite = 0;
       VVA_ONLY(rc =) sqlite3WalFindFrame(pWal, p->pgno, &iWrite);