Import SQLite 3.7.6.3.

third_party/sqlite/src/src/test_superlock.c

+/*
+** 2010 November 19
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+*************************************************************************
+** Example code for obtaining an exclusive lock on an SQLite database
+** file. This method is complicated, but works for both WAL and rollback
+** mode database files. The interface to the example code in this file 
+** consists of the following two functions:
+**
+**   sqlite3demo_superlock()
+**   sqlite3demo_superunlock()
+*/
+
+#include <sqlite3.h>
+#include <string.h>               /* memset(), strlen() */
+#include <assert.h>               /* assert() */
+
+/*
+** A structure to collect a busy-handler callback and argument and a count
+** of the number of times it has been invoked.
+*/
+struct SuperlockBusy {
+  int (*xBusy)(void*,int);        /* Pointer to busy-handler function */
+  void *pBusyArg;                 /* First arg to pass to xBusy */
+  int nBusy;                      /* Number of times xBusy has been invoked */
+};
+typedef struct SuperlockBusy SuperlockBusy;
+
+/*
+** An instance of the following structure is allocated for each active
+** superlock. The opaque handle returned by sqlite3demo_superlock() is
+** actually a pointer to an instance of this structure.
+*/
+struct Superlock {
+  sqlite3 *db;                    /* Database handle used to lock db */
+  int bWal;                       /* True if db is a WAL database */
+};
+typedef struct Superlock Superlock;
+
+/*
+** The pCtx pointer passed to this function is actually a pointer to a
+** SuperlockBusy structure. Invoke the busy-handler function encapsulated
+** by the structure and return the result.
+*/
+static int superlockBusyHandler(void *pCtx, int UNUSED){
+  SuperlockBusy *pBusy = (SuperlockBusy *)pCtx;
+  if( pBusy->xBusy==0 ) return 0;
+  return pBusy->xBusy(pBusy->pBusyArg, pBusy->nBusy++);
+}
+
+/*
+** This function is used to determine if the main database file for 
+** connection db is open in WAL mode or not. If no error occurs and the
+** database file is in WAL mode, set *pbWal to true and return SQLITE_OK.
+** If it is not in WAL mode, set *pbWal to false.
+**
+** If an error occurs, return an SQLite error code. The value of *pbWal
+** is undefined in this case.
+*/
+static int superlockIsWal(Superlock *pLock){
+  int rc;                         /* Return Code */
+  sqlite3_stmt *pStmt;            /* Compiled PRAGMA journal_mode statement */
+
+  rc = sqlite3_prepare(pLock->db, "PRAGMA main.journal_mode", -1, &pStmt, 0);
+  if( rc!=SQLITE_OK ) return rc;
+
+  pLock->bWal = 0;
+  if( SQLITE_ROW==sqlite3_step(pStmt) ){
+    const char *zMode = (const char *)sqlite3_column_text(pStmt, 0);
+    if( zMode && strlen(zMode)==3 && sqlite3_strnicmp("wal", zMode, 3)==0 ){
+      pLock->bWal = 1;
+    }
+  }
+
+  return sqlite3_finalize(pStmt);
+}
+
+/*
+** Obtain an exclusive shm-lock on nByte bytes starting at offset idx
+** of the file fd. If the lock cannot be obtained immediately, invoke
+** the busy-handler until either it is obtained or the busy-handler
+** callback returns 0.
+*/
+static int superlockShmLock(
+  sqlite3_file *fd,               /* Database file handle */
+  int idx,                        /* Offset of shm-lock to obtain */
+  int nByte,                      /* Number of consective bytes to lock */
+  SuperlockBusy *pBusy            /* Busy-handler wrapper object */
+){
+  int rc;
+  int (*xShmLock)(sqlite3_file*, int, int, int) = fd->pMethods->xShmLock;
+  do {
+    rc = xShmLock(fd, idx, nByte, SQLITE_SHM_LOCK|SQLITE_SHM_EXCLUSIVE);
+  }while( rc==SQLITE_BUSY && superlockBusyHandler((void *)pBusy, 0) );
+  return rc;
+}
+
+/*
+** Obtain the extra locks on the database file required for WAL databases.
+** Invoke the supplied busy-handler as required.
+*/
+static int superlockWalLock(
+  sqlite3 *db,                    /* Database handle open on WAL database */
+  SuperlockBusy *pBusy            /* Busy handler wrapper object */
+){
+  int rc;                         /* Return code */
+  sqlite3_file *fd = 0;           /* Main database file handle */
+  void volatile *p = 0;           /* Pointer to first page of shared memory */
+
+  /* Obtain a pointer to the sqlite3_file object open on the main db file. */
+  rc = sqlite3_file_control(db, "main", SQLITE_FCNTL_FILE_POINTER, (void *)&fd);
+  if( rc!=SQLITE_OK ) return rc;
+
+  /* Obtain the "recovery" lock. Normally, this lock is only obtained by
+  ** clients running database recovery.  
+  */
+  rc = superlockShmLock(fd, 2, 1, pBusy);
+  if( rc!=SQLITE_OK ) return rc;
+
+  /* Zero the start of the first shared-memory page. This means that any
+  ** clients that open read or write transactions from this point on will
+  ** have to run recovery before proceeding. Since they need the "recovery"
+  ** lock that this process is holding to do that, no new read or write
+  ** transactions may now be opened. Nor can a checkpoint be run, for the
+  ** same reason.
+  */
+  rc = fd->pMethods->xShmMap(fd, 0, 32*1024, 1, &p);
+  if( rc!=SQLITE_OK ) return rc;
+  memset((void *)p, 0, 32);
+
+  /* Obtain exclusive locks on all the "read-lock" slots. Once these locks
+  ** are held, it is guaranteed that there are no active reader, writer or 
+  ** checkpointer clients.
+  */
+  rc = superlockShmLock(fd, 3, SQLITE_SHM_NLOCK-3, pBusy);
+  return rc;
+}
+
+/*
+** Release a superlock held on a database file. The argument passed to 
+** this function must have been obtained from a successful call to
+** sqlite3demo_superlock().
+*/
+void sqlite3demo_superunlock(void *pLock){
+  Superlock *p = (Superlock *)pLock;
+  if( p->bWal ){
+    int rc;                         /* Return code */
+    int flags = SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE;
+    sqlite3_file *fd = 0;
+    rc = sqlite3_file_control(p->db, "main", SQLITE_FCNTL_FILE_POINTER, (void *)&fd);
+    if( rc==SQLITE_OK ){
+      fd->pMethods->xShmLock(fd, 2, 1, flags);
+      fd->pMethods->xShmLock(fd, 3, SQLITE_SHM_NLOCK-3, flags);
+    }
+  }
+  sqlite3_close(p->db);
+  sqlite3_free(p);
+}
+
+/*
+** Obtain a superlock on the database file identified by zPath, using the
+** locking primitives provided by VFS zVfs. If successful, SQLITE_OK is
+** returned and output variable *ppLock is populated with an opaque handle
+** that may be used with sqlite3demo_superunlock() to release the lock.
+**
+** If an error occurs, *ppLock is set to 0 and an SQLite error code 
+** (e.g. SQLITE_BUSY) is returned.
+**
+** If a required lock cannot be obtained immediately and the xBusy parameter
+** to this function is not NULL, then xBusy is invoked in the same way
+** as a busy-handler registered with SQLite (using sqlite3_busy_handler())
+** until either the lock can be obtained or the busy-handler function returns
+** 0 (indicating "give up").
+*/
+int sqlite3demo_superlock(
+  const char *zPath,              /* Path to database file to lock */
+  const char *zVfs,               /* VFS to use to access database file */
+  int (*xBusy)(void*,int),        /* Busy handler callback */
+  void *pBusyArg,                 /* Context arg for busy handler */
+  void **ppLock                   /* OUT: Context to pass to superunlock() */
+){
+  SuperlockBusy busy = {0, 0, 0}; /* Busy handler wrapper object */
+  int rc;                         /* Return code */
+  Superlock *pLock;
+
+  pLock = sqlite3_malloc(sizeof(Superlock));
+  if( !pLock ) return SQLITE_NOMEM;
+  memset(pLock, 0, sizeof(Superlock));
+
+  /* Open a database handle on the file to superlock. */
+  rc = sqlite3_open_v2(
+      zPath, &pLock->db, SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE, zVfs
+  );
+
+  /* Install a busy-handler and execute a BEGIN EXCLUSIVE. If this is not
+  ** a WAL database, this is all we need to do.  
+  **
+  ** A wrapper function is used to invoke the busy-handler instead of
+  ** registering the busy-handler function supplied by the user directly
+  ** with SQLite. This is because the same busy-handler function may be
+  ** invoked directly later on when attempting to obtain the extra locks
+  ** required in WAL mode. By using the wrapper, we are able to guarantee
+  ** that the "nBusy" integer parameter passed to the users busy-handler
+  ** represents the total number of busy-handler invocations made within
+  ** this call to sqlite3demo_superlock(), including any made during the
+  ** "BEGIN EXCLUSIVE".
+  */
+  if( rc==SQLITE_OK ){
+    busy.xBusy = xBusy;
+    busy.pBusyArg = pBusyArg;
+    sqlite3_busy_handler(pLock->db, superlockBusyHandler, (void *)&busy);
+    rc = sqlite3_exec(pLock->db, "BEGIN EXCLUSIVE", 0, 0, 0);
+  }
+
+  /* If the BEGIN EXCLUSIVE was executed successfully and this is a WAL
+  ** database, call superlockWalLock() to obtain the extra locks required
+  ** to prevent readers, writers and/or checkpointers from accessing the
+  ** db while this process is holding the superlock.
+  **
+  ** Before attempting any WAL locks, commit the transaction started above
+  ** to drop the WAL read and write locks currently held. Otherwise, the
+  ** new WAL locks may conflict with the old.
+  */
+  if( rc==SQLITE_OK ){
+    if( SQLITE_OK==(rc = superlockIsWal(pLock)) && pLock->bWal ){
+      rc = sqlite3_exec(pLock->db, "COMMIT", 0, 0, 0);
+      if( rc==SQLITE_OK ){
+        rc = superlockWalLock(pLock->db, &busy);
+      }
+    }
+  }
+
+  if( rc!=SQLITE_OK ){
+    sqlite3demo_superunlock(pLock);
+    *ppLock = 0;
+  }else{
+    *ppLock = pLock;
+  }
+
+  return rc;
+}
+
+/*
+** End of example code. Everything below here is the test harness.
+**************************************************************************
+**************************************************************************
+*************************************************************************/
+
+
+#ifdef SQLITE_TEST
+
+#include <tcl.h>
+
+struct InterpAndScript {
+  Tcl_Interp *interp;
+  Tcl_Obj *pScript;
+};
+typedef struct InterpAndScript InterpAndScript;
+
+static void superunlock_del(ClientData cd){
+  sqlite3demo_superunlock((void *)cd);
+}
+
+static int superunlock_cmd(
+  ClientData cd,
+  Tcl_Interp *interp,
+  int objc,
+  Tcl_Obj *CONST objv[]
+){
+  if( objc!=1 ){
+    Tcl_WrongNumArgs(interp, 1, objv, "");
+    return TCL_ERROR;
+  }
+  Tcl_DeleteCommand(interp, Tcl_GetString(objv[0]));
+  return TCL_OK;
+}
+
+static int superlock_busy(void *pCtx, int nBusy){
+  InterpAndScript *p = (InterpAndScript *)pCtx;
+  Tcl_Obj *pEval;                 /* Script to evaluate */
+  int iVal = 0;                   /* Value to return */
+
+  pEval = Tcl_DuplicateObj(p->pScript);
+  Tcl_IncrRefCount(pEval);
+  Tcl_ListObjAppendElement(p->interp, pEval, Tcl_NewIntObj(nBusy));
+  Tcl_EvalObjEx(p->interp, pEval, TCL_EVAL_GLOBAL);
+  Tcl_GetIntFromObj(p->interp, Tcl_GetObjResult(p->interp), &iVal);
+  Tcl_DecrRefCount(pEval);
+
+  return iVal;
+}
+
+/*
+** Tclcmd: sqlite3demo_superlock CMDNAME PATH VFS BUSY-HANDLER-SCRIPT
+*/
+static int superlock_cmd(
+  ClientData cd,
+  Tcl_Interp *interp,
+  int objc,
+  Tcl_Obj *CONST objv[]
+){
+  void *pLock;                    /* Lock context */
+  char *zPath;
+  char *zVfs = 0;
+  InterpAndScript busy = {0, 0};
+  int (*xBusy)(void*,int) = 0;    /* Busy handler callback */
+  int rc;                         /* Return code from sqlite3demo_superlock() */
+
+  if( objc<3 || objc>5 ){
+    Tcl_WrongNumArgs(
+        interp, 1, objv, "CMDNAME PATH ?VFS? ?BUSY-HANDLER-SCRIPT?");
+    return TCL_ERROR;
+  }
+
+  zPath = Tcl_GetString(objv[2]);
+
+  if( objc>3 ){
+    zVfs = Tcl_GetString(objv[3]);
+    if( strlen(zVfs)==0 ) zVfs = 0;
+  }
+  if( objc>4 ){
+    busy.interp = interp;
+    busy.pScript = objv[4];
+    xBusy = superlock_busy;
+  }
+
+  rc = sqlite3demo_superlock(zPath, zVfs, xBusy, &busy, &pLock);
+  assert( rc==SQLITE_OK || pLock==0 );
+  assert( rc!=SQLITE_OK || pLock!=0 );
+
+  if( rc!=SQLITE_OK ){
+    extern const char *sqlite3ErrStr(int);
+    Tcl_ResetResult(interp);
+    Tcl_AppendResult(interp, sqlite3ErrStr(rc), 0);
+    return TCL_ERROR;
+  }
+
+  Tcl_CreateObjCommand(
+      interp, Tcl_GetString(objv[1]), superunlock_cmd, pLock, superunlock_del
+  );
+  Tcl_SetObjResult(interp, objv[1]);
+  return TCL_OK;
+}
+
+int SqliteSuperlock_Init(Tcl_Interp *interp){
+  Tcl_CreateObjCommand(interp, "sqlite3demo_superlock", superlock_cmd, 0, 0);
+  return TCL_OK;
+}
+#endif