src/test_thread.c

   1 /*
   2 ** 2007 September 9
   3 **
   4 ** The author disclaims copyright to this source code.  In place of
   5 ** a legal notice, here is a blessing:
   6 **
   7 **    May you do good and not evil.
   8 **    May you find forgiveness for yourself and forgive others.
   9 **    May you share freely, never taking more than you give.
  10 **
  11 *************************************************************************
  12 **
  13 ** This file contains the implementation of some Tcl commands used to
  14 ** test that sqlite3 database handles may be concurrently accessed by
  15 ** multiple threads. Right now this only works on unix.
  16 */
  17
  18 #include "sqliteInt.h"
  19 #include <tcl.h>
  20
  21 #if SQLITE_THREADSAFE
  22
  23 #include <errno.h>
  24
  25 #if !defined(_MSC_VER)
  26 #include <unistd.h>
  27 #endif
  28
  29 /*
  30 ** One of these is allocated for each thread created by [sqlthread spawn].
  31 */
  32 typedef struct SqlThread SqlThread;
  33 struct SqlThread {
  34   Tcl_ThreadId parent;     /* Thread id of parent thread */
  35   Tcl_Interp *interp;      /* Parent interpreter */
  36   char *zScript;           /* The script to execute. */
  37   char *zVarname;          /* Varname in parent script */
  38 };
  39
  40 /*
  41 ** A custom Tcl_Event type used by this module. When the event is
  42 ** handled, script zScript is evaluated in interpreter interp. If
  43 ** the evaluation throws an exception (returns TCL_ERROR), then the
  44 ** error is handled by Tcl_BackgroundError(). If no error occurs,
  45 ** the result is simply discarded.
  46 */
  47 typedef struct EvalEvent EvalEvent;
  48 struct EvalEvent {
  49   Tcl_Event base;          /* Base class of type Tcl_Event */
  50   char *zScript;           /* The script to execute. */
  51   Tcl_Interp *interp;      /* The interpreter to execute it in. */
  52 };
  53
  54 static Tcl_ObjCmdProc sqlthread_proc;
  55 static Tcl_ObjCmdProc clock_seconds_proc;
  56 #if SQLITE_OS_UNIX && defined(SQLITE_ENABLE_UNLOCK_NOTIFY)
  57 static Tcl_ObjCmdProc blocking_step_proc;
  58 static Tcl_ObjCmdProc blocking_prepare_v2_proc;
  59 #endif
  60 int Sqlitetest1_Init(Tcl_Interp *);
  61 int Sqlite3_Init(Tcl_Interp *);
  62
  63 /* Functions from main.c */
  64 extern const char *sqlite3ErrName(int);
  65
  66 /* Functions from test1.c */
  67 extern void *sqlite3TestTextToPtr(const char *);
  68 extern int getDbPointer(Tcl_Interp *, const char *, sqlite3 **);
  69 extern int sqlite3TestMakePointerStr(Tcl_Interp *, char *, void *);
  70 extern int sqlite3TestErrCode(Tcl_Interp *, sqlite3 *, int);
  71
  72 /*
  73 ** Handler for events of type EvalEvent.
  74 */
  75 static int tclScriptEvent(Tcl_Event *evPtr, int flags){
  76   int rc;
  77   EvalEvent *p = (EvalEvent *)evPtr;
  78   rc = Tcl_Eval(p->interp, p->zScript);
  79   if( rc!=TCL_OK ){
  80     Tcl_BackgroundError(p->interp);
  81   }
  82   UNUSED_PARAMETER(flags);
  83   return 1;
  84 }
  85
  86 /*
  87 ** Register an EvalEvent to evaluate the script pScript in the
  88 ** parent interpreter/thread of SqlThread p.
  89 */
  90 static void postToParent(SqlThread *p, Tcl_Obj *pScript){
  91   EvalEvent *pEvent;
  92   char *zMsg;
  93   int nMsg;
  94
  95   zMsg = Tcl_GetStringFromObj(pScript, &nMsg);
  96   pEvent = (EvalEvent *)ckalloc(sizeof(EvalEvent)+nMsg+1);
  97   pEvent->base.nextPtr = 0;
  98   pEvent->base.proc = tclScriptEvent;
  99   pEvent->zScript = (char *)&pEvent[1];
 100   memcpy(pEvent->zScript, zMsg, nMsg+1);
 101   pEvent->interp = p->interp;
 102
 103   Tcl_ThreadQueueEvent(p->parent, (Tcl_Event *)pEvent, TCL_QUEUE_TAIL);
 104   Tcl_ThreadAlert(p->parent);
 105 }
 106
 107 /*
 108 ** The main function for threads created with [sqlthread spawn].
 109 */
 110 static Tcl_ThreadCreateType tclScriptThread(ClientData pSqlThread){
 111   Tcl_Interp *interp;
 112   Tcl_Obj *pRes;
 113   Tcl_Obj *pList;
 114   int rc;
 115   SqlThread *p = (SqlThread *)pSqlThread;
 116   extern int Sqlitetest_mutex_Init(Tcl_Interp*);
 117
 118   interp = Tcl_CreateInterp();
 119   Tcl_CreateObjCommand(interp, "clock_seconds", clock_seconds_proc, 0, 0);
 120   Tcl_CreateObjCommand(interp, "sqlthread", sqlthread_proc, pSqlThread, 0);
 121 #if SQLITE_OS_UNIX && defined(SQLITE_ENABLE_UNLOCK_NOTIFY)
 122   Tcl_CreateObjCommand(interp, "sqlite3_blocking_step", blocking_step_proc,0,0);
 123   Tcl_CreateObjCommand(interp,
 124       "sqlite3_blocking_prepare_v2", blocking_prepare_v2_proc, (void *)1, 0);
 125   Tcl_CreateObjCommand(interp,
 126       "sqlite3_nonblocking_prepare_v2", blocking_prepare_v2_proc, 0, 0);
 127 #endif
 128   Sqlitetest1_Init(interp);
 129   Sqlitetest_mutex_Init(interp);
 130   Sqlite3_Init(interp);
 131
 132   rc = Tcl_Eval(interp, p->zScript);
 133   pRes = Tcl_GetObjResult(interp);
 134   pList = Tcl_NewObj();
 135   Tcl_IncrRefCount(pList);
 136   Tcl_IncrRefCount(pRes);
 137
 138   if( rc!=TCL_OK ){
 139     Tcl_ListObjAppendElement(interp, pList, Tcl_NewStringObj("error", -1));
 140     Tcl_ListObjAppendElement(interp, pList, pRes);
 141     postToParent(p, pList);
 142     Tcl_DecrRefCount(pList);
 143     pList = Tcl_NewObj();
 144   }
 145
 146   Tcl_ListObjAppendElement(interp, pList, Tcl_NewStringObj("set", -1));
 147   Tcl_ListObjAppendElement(interp, pList, Tcl_NewStringObj(p->zVarname, -1));
 148   Tcl_ListObjAppendElement(interp, pList, pRes);
 149   postToParent(p, pList);
 150
 151   ckfree((void *)p);
 152   Tcl_DecrRefCount(pList);
 153   Tcl_DecrRefCount(pRes);
 154   Tcl_DeleteInterp(interp);
 155   while( Tcl_DoOneEvent(TCL_ALL_EVENTS|TCL_DONT_WAIT) );
 156   Tcl_ExitThread(0);
 157   TCL_THREAD_CREATE_RETURN;
 158 }
 159
 160 /*
 161 ** sqlthread spawn VARNAME SCRIPT
 162 **
 163 **     Spawn a new thread with its own Tcl interpreter and run the
 164 **     specified SCRIPT(s) in it. The thread terminates after running
 165 **     the script. The result of the script is stored in the variable
 166 **     VARNAME.
 167 **
 168 **     The caller can wait for the script to terminate using [vwait VARNAME].
 169 */
 170 static int sqlthread_spawn(
 171   ClientData clientData,
 172   Tcl_Interp *interp,
 173   int objc,
 174   Tcl_Obj *CONST objv[]
 175 ){
 176   Tcl_ThreadId x;
 177   SqlThread *pNew;
 178   int rc;
 179
 180   int nVarname; char *zVarname;
 181   int nScript; char *zScript;
 182
 183   /* Parameters for thread creation */
 184   const int nStack = TCL_THREAD_STACK_DEFAULT;
 185   const int flags = TCL_THREAD_NOFLAGS;
 186
 187   assert(objc==4);
 188   UNUSED_PARAMETER(clientData);
 189   UNUSED_PARAMETER(objc);
 190
 191   zVarname = Tcl_GetStringFromObj(objv[2], &nVarname);
 192   zScript = Tcl_GetStringFromObj(objv[3], &nScript);
 193
 194   pNew = (SqlThread *)ckalloc(sizeof(SqlThread)+nVarname+nScript+2);
 195   pNew->zVarname = (char *)&pNew[1];
 196   pNew->zScript = (char *)&pNew->zVarname[nVarname+1];
 197   memcpy(pNew->zVarname, zVarname, nVarname+1);
 198   memcpy(pNew->zScript, zScript, nScript+1);
 199   pNew->parent = Tcl_GetCurrentThread();
 200   pNew->interp = interp;
 201
 202   rc = Tcl_CreateThread(&x, tclScriptThread, (void *)pNew, nStack, flags);
 203   if( rc!=TCL_OK ){
 204     Tcl_AppendResult(interp, "Error in Tcl_CreateThread()", 0);
 205     ckfree((char *)pNew);
 206     return TCL_ERROR;
 207   }
 208
 209   return TCL_OK;
 210 }
 211
 212 /*
 213 ** sqlthread parent SCRIPT
 214 **
 215 **     This can be called by spawned threads only. It sends the specified
 216 **     script back to the parent thread for execution. The result of
 217 **     evaluating the SCRIPT is returned. The parent thread must enter
 218 **     the event loop for this to work - otherwise the caller will
 219 **     block indefinitely.
 220 **
 221 **     NOTE: At the moment, this doesn't work. FIXME.
 222 */
 223 static int sqlthread_parent(
 224   ClientData clientData,
 225   Tcl_Interp *interp,
 226   int objc,
 227   Tcl_Obj *CONST objv[]
 228 ){
 229   EvalEvent *pEvent;
 230   char *zMsg;
 231   int nMsg;
 232   SqlThread *p = (SqlThread *)clientData;
 233
 234   assert(objc==3);
 235   UNUSED_PARAMETER(objc);
 236
 237   if( p==0 ){
 238     Tcl_AppendResult(interp, "no parent thread", 0);
 239     return TCL_ERROR;
 240   }
 241
 242   zMsg = Tcl_GetStringFromObj(objv[2], &nMsg);
 243   pEvent = (EvalEvent *)ckalloc(sizeof(EvalEvent)+nMsg+1);
 244   pEvent->base.nextPtr = 0;
 245   pEvent->base.proc = tclScriptEvent;
 246   pEvent->zScript = (char *)&pEvent[1];
 247   memcpy(pEvent->zScript, zMsg, nMsg+1);
 248   pEvent->interp = p->interp;
 249   Tcl_ThreadQueueEvent(p->parent, (Tcl_Event *)pEvent, TCL_QUEUE_TAIL);
 250   Tcl_ThreadAlert(p->parent);
 251
 252   return TCL_OK;
 253 }
 254
 255 static int xBusy(void *pArg, int nBusy){
 256   UNUSED_PARAMETER(pArg);
 257   UNUSED_PARAMETER(nBusy);
 258   sqlite3_sleep(50);
 259   return 1;             /* Try again... */
 260 }
 261
 262 /*
 263 ** sqlthread open
 264 **
 265 **     Open a database handle and return the string representation of
 266 **     the pointer value.
 267 */
 268 static int sqlthread_open(
 269   ClientData clientData,
 270   Tcl_Interp *interp,
 271   int objc,
 272   Tcl_Obj *CONST objv[]
 273 ){
 274   int sqlite3TestMakePointerStr(Tcl_Interp *interp, char *zPtr, void *p);
 275
 276   const char *zFilename;
 277   sqlite3 *db;
 278   char zBuf[100];
 279   extern void Md5_Register(sqlite3*);
 280
 281   UNUSED_PARAMETER(clientData);
 282   UNUSED_PARAMETER(objc);
 283
 284   zFilename = Tcl_GetString(objv[2]);
 285   sqlite3_open(zFilename, &db);
 286 #ifdef SQLITE_HAS_CODEC
 287   if( db && objc>=4 ){
 288     const char *zKey;
 289     int nKey;
 290     int rc;
 291     zKey = Tcl_GetStringFromObj(objv[3], &nKey);
 292     rc = sqlite3_key(db, zKey, nKey);
 293     if( rc!=SQLITE_OK ){
 294       char *zErrMsg = sqlite3_mprintf("error %d: %s", rc, sqlite3_errmsg(db));
 295       sqlite3_close(db);
 296       Tcl_AppendResult(interp, zErrMsg, (char*)0);
 297       sqlite3_free(zErrMsg);
 298       return TCL_ERROR;
 299     }
 300   }
 301 #endif
 302   Md5_Register(db);
 303   sqlite3_busy_handler(db, xBusy, 0);
 304
 305   if( sqlite3TestMakePointerStr(interp, zBuf, db) ) return TCL_ERROR;
 306   Tcl_AppendResult(interp, zBuf, 0);
 307
 308   return TCL_OK;
 309 }
 310
 311
 312 /*
 313 ** sqlthread open
 314 **
 315 **     Return the current thread-id (Tcl_GetCurrentThread()) cast to
 316 **     an integer.
 317 */
 318 static int sqlthread_id(
 319   ClientData clientData,
 320   Tcl_Interp *interp,
 321   int objc,
 322   Tcl_Obj *CONST objv[]
 323 ){
 324   Tcl_ThreadId id = Tcl_GetCurrentThread();
 325   Tcl_SetObjResult(interp, Tcl_NewIntObj(SQLITE_PTR_TO_INT(id)));
 326   UNUSED_PARAMETER(clientData);
 327   UNUSED_PARAMETER(objc);
 328   UNUSED_PARAMETER(objv);
 329   return TCL_OK;
 330 }
 331
 332
 333 /*
 334 ** Dispatch routine for the sub-commands of [sqlthread].
 335 */
 336 static int sqlthread_proc(
 337   ClientData clientData,
 338   Tcl_Interp *interp,
 339   int objc,
 340   Tcl_Obj *CONST objv[]
 341 ){
 342   struct SubCommand {
 343     char *zName;
 344     Tcl_ObjCmdProc *xProc;
 345     int nArg;
 346     char *zUsage;
 347   } aSub[] = {
 348     {"parent", sqlthread_parent, 1, "SCRIPT"},
 349     {"spawn",  sqlthread_spawn,  2, "VARNAME SCRIPT"},
 350     {"open",   sqlthread_open,   1, "DBNAME"},
 351     {"id",     sqlthread_id,     0, ""},
 352     {0, 0, 0}
 353   };
 354   struct SubCommand *pSub;
 355   int rc;
 356   int iIndex;
 357
 358   if( objc<2 ){
 359     Tcl_WrongNumArgs(interp, 1, objv, "SUB-COMMAND");
 360     return TCL_ERROR;
 361   }
 362
 363   rc = Tcl_GetIndexFromObjStruct(
 364       interp, objv[1], aSub, sizeof(aSub[0]), "sub-command", 0, &iIndex
 365   );
 366   if( rc!=TCL_OK ) return rc;
 367   pSub = &aSub[iIndex];
 368
 369   if( objc<(pSub->nArg+2) ){
 370     Tcl_WrongNumArgs(interp, 2, objv, pSub->zUsage);
 371     return TCL_ERROR;
 372   }
 373
 374   return pSub->xProc(clientData, interp, objc, objv);
 375 }
 376
 377 /*
 378 ** The [clock_seconds] command. This is more or less the same as the
 379 ** regular tcl [clock seconds], except that it is available in testfixture
 380 ** when linked against both Tcl 8.4 and 8.5. Because [clock seconds] is
 381 ** implemented as a script in Tcl 8.5, it is not usually available to
 382 ** testfixture.
 383 */
 384 static int clock_seconds_proc(
 385   ClientData clientData,
 386   Tcl_Interp *interp,
 387   int objc,
 388   Tcl_Obj *CONST objv[]
 389 ){
 390   Tcl_Time now;
 391   Tcl_GetTime(&now);
 392   Tcl_SetObjResult(interp, Tcl_NewIntObj(now.sec));
 393   UNUSED_PARAMETER(clientData);
 394   UNUSED_PARAMETER(objc);
 395   UNUSED_PARAMETER(objv);
 396   return TCL_OK;
 397 }
 398
 399 /*************************************************************************
 400 ** This block contains the implementation of the [sqlite3_blocking_step]
 401 ** command available to threads created by [sqlthread spawn] commands. It
 402 ** is only available on UNIX for now. This is because pthread condition
 403 ** variables are used.
 404 **
 405 ** The source code for the C functions sqlite3_blocking_step(),
 406 ** blocking_step_notify() and the structure UnlockNotification is
 407 ** automatically extracted from this file and used as part of the
 408 ** documentation for the sqlite3_unlock_notify() API function. This
 409 ** should be considered if these functions are to be extended (i.e. to
 410 ** support windows) in the future.
 411 */
 412 #if SQLITE_OS_UNIX && defined(SQLITE_ENABLE_UNLOCK_NOTIFY)
 413
 414 /* BEGIN_SQLITE_BLOCKING_STEP */
 415 /* This example uses the pthreads API */
 416 #include <pthread.h>
 417
 418 /*
 419 ** A pointer to an instance of this structure is passed as the user-context
 420 ** pointer when registering for an unlock-notify callback.
 421 */
 422 typedef struct UnlockNotification UnlockNotification;
 423 struct UnlockNotification {
 424   int fired;                         /* True after unlock event has occurred */
 425   pthread_cond_t cond;               /* Condition variable to wait on */
 426   pthread_mutex_t mutex;             /* Mutex to protect structure */
 427 };
 428
 429 /*
 430 ** This function is an unlock-notify callback registered with SQLite.
 431 */
 432 static void unlock_notify_cb(void **apArg, int nArg){
 433   int i;
 434   for(i=0; i<nArg; i++){
 435     UnlockNotification *p = (UnlockNotification *)apArg[i];
 436     pthread_mutex_lock(&p->mutex);
 437     p->fired = 1;
 438     pthread_cond_signal(&p->cond);
 439     pthread_mutex_unlock(&p->mutex);
 440   }
 441 }
 442
 443 /*
 444 ** This function assumes that an SQLite API call (either sqlite3_prepare_v2()
 445 ** or sqlite3_step()) has just returned SQLITE_LOCKED. The argument is the
 446 ** associated database connection.
 447 **
 448 ** This function calls sqlite3_unlock_notify() to register for an
 449 ** unlock-notify callback, then blocks until that callback is delivered
 450 ** and returns SQLITE_OK. The caller should then retry the failed operation.
 451 **
 452 ** Or, if sqlite3_unlock_notify() indicates that to block would deadlock
 453 ** the system, then this function returns SQLITE_LOCKED immediately. In
 454 ** this case the caller should not retry the operation and should roll
 455 ** back the current transaction (if any).
 456 */
 457 static int wait_for_unlock_notify(sqlite3 *db){
 458   int rc;
 459   UnlockNotification un;
 460
 461   /* Initialize the UnlockNotification structure. */
 462   un.fired = 0;
 463   pthread_mutex_init(&un.mutex, 0);
 464   pthread_cond_init(&un.cond, 0);
 465
 466   /* Register for an unlock-notify callback. */
 467   rc = sqlite3_unlock_notify(db, unlock_notify_cb, (void *)&un);
 468   assert( rc==SQLITE_LOCKED || rc==SQLITE_OK );
 469
 470   /* The call to sqlite3_unlock_notify() always returns either SQLITE_LOCKED
 471   ** or SQLITE_OK.
 472   **
 473   ** If SQLITE_LOCKED was returned, then the system is deadlocked. In this
 474   ** case this function needs to return SQLITE_LOCKED to the caller so
 475   ** that the current transaction can be rolled back. Otherwise, block
 476   ** until the unlock-notify callback is invoked, then return SQLITE_OK.
 477   */
 478   if( rc==SQLITE_OK ){
 479     pthread_mutex_lock(&un.mutex);
 480     if( !un.fired ){
 481       pthread_cond_wait(&un.cond, &un.mutex);
 482     }
 483     pthread_mutex_unlock(&un.mutex);
 484   }
 485
 486   /* Destroy the mutex and condition variables. */
 487   pthread_cond_destroy(&un.cond);
 488   pthread_mutex_destroy(&un.mutex);
 489
 490   return rc;
 491 }
 492
 493 /*
 494 ** This function is a wrapper around the SQLite function sqlite3_step().
 495 ** It functions in the same way as step(), except that if a required
 496 ** shared-cache lock cannot be obtained, this function may block waiting for
 497 ** the lock to become available. In this scenario the normal API step()
 498 ** function always returns SQLITE_LOCKED.
 499 **
 500 ** If this function returns SQLITE_LOCKED, the caller should rollback
 501 ** the current transaction (if any) and try again later. Otherwise, the
 502 ** system may become deadlocked.
 503 */
 504 int sqlite3_blocking_step(sqlite3_stmt *pStmt){
 505   int rc;
 506   while( SQLITE_LOCKED==(rc = sqlite3_step(pStmt)) ){
 507     rc = wait_for_unlock_notify(sqlite3_db_handle(pStmt));
 508     if( rc!=SQLITE_OK ) break;
 509     sqlite3_reset(pStmt);
 510   }
 511   return rc;
 512 }
 513
 514 /*
 515 ** This function is a wrapper around the SQLite function sqlite3_prepare_v2().
 516 ** It functions in the same way as prepare_v2(), except that if a required
 517 ** shared-cache lock cannot be obtained, this function may block waiting for
 518 ** the lock to become available. In this scenario the normal API prepare_v2()
 519 ** function always returns SQLITE_LOCKED.
 520 **
 521 ** If this function returns SQLITE_LOCKED, the caller should rollback
 522 ** the current transaction (if any) and try again later. Otherwise, the
 523 ** system may become deadlocked.
 524 */
 525 int sqlite3_blocking_prepare_v2(
 526   sqlite3 *db,              /* Database handle. */
 527   const char *zSql,         /* UTF-8 encoded SQL statement. */
 528   int nSql,                 /* Length of zSql in bytes. */
 529   sqlite3_stmt **ppStmt,    /* OUT: A pointer to the prepared statement */
 530   const char **pz           /* OUT: End of parsed string */
 531 ){
 532   int rc;
 533   while( SQLITE_LOCKED==(rc = sqlite3_prepare_v2(db, zSql, nSql, ppStmt, pz)) ){
 534     rc = wait_for_unlock_notify(db);
 535     if( rc!=SQLITE_OK ) break;
 536   }
 537   return rc;
 538 }
 539 /* END_SQLITE_BLOCKING_STEP */
 540
 541 /*
 542 ** Usage: sqlite3_blocking_step STMT
 543 **
 544 ** Advance the statement to the next row.
 545 */
 546 static int blocking_step_proc(
 547   void * clientData,
 548   Tcl_Interp *interp,
 549   int objc,
 550   Tcl_Obj *CONST objv[]
 551 ){
 552
 553   sqlite3_stmt *pStmt;
 554   int rc;
 555
 556   if( objc!=2 ){
 557     Tcl_WrongNumArgs(interp, 1, objv, "STMT");
 558     return TCL_ERROR;
 559   }
 560
 561   pStmt = (sqlite3_stmt*)sqlite3TestTextToPtr(Tcl_GetString(objv[1]));
 562   rc = sqlite3_blocking_step(pStmt);
 563
 564   Tcl_SetResult(interp, (char *)sqlite3ErrName(rc), 0);
 565   return TCL_OK;
 566 }
 567
 568 /*
 569 ** Usage: sqlite3_blocking_prepare_v2 DB sql bytes ?tailvar?
 570 ** Usage: sqlite3_nonblocking_prepare_v2 DB sql bytes ?tailvar?
 571 */
 572 static int blocking_prepare_v2_proc(
 573   void * clientData,
 574   Tcl_Interp *interp,
 575   int objc,
 576   Tcl_Obj *CONST objv[]
 577 ){
 578   sqlite3 *db;
 579   const char *zSql;
 580   int bytes;
 581   const char *zTail = 0;
 582   sqlite3_stmt *pStmt = 0;
 583   char zBuf[50];
 584   int rc;
 585   int isBlocking = !(clientData==0);
 586
 587   if( objc!=5 && objc!=4 ){
 588     Tcl_AppendResult(interp, "wrong # args: should be \"",
 589        Tcl_GetString(objv[0]), " DB sql bytes tailvar", 0);
 590     return TCL_ERROR;
 591   }
 592   if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
 593   zSql = Tcl_GetString(objv[2]);
 594   if( Tcl_GetIntFromObj(interp, objv[3], &bytes) ) return TCL_ERROR;
 595
 596   if( isBlocking ){
 597     rc = sqlite3_blocking_prepare_v2(db, zSql, bytes, &pStmt, &zTail);
 598   }else{
 599     rc = sqlite3_prepare_v2(db, zSql, bytes, &pStmt, &zTail);
 600   }
 601
 602   assert(rc==SQLITE_OK || pStmt==0);
 603   if( zTail && objc>=5 ){
 604     if( bytes>=0 ){
 605       bytes = bytes - (zTail-zSql);
 606     }
 607     Tcl_ObjSetVar2(interp, objv[4], 0, Tcl_NewStringObj(zTail, bytes), 0);
 608   }
 609   if( rc!=SQLITE_OK ){
 610     assert( pStmt==0 );
 611     sprintf(zBuf, "%s ", (char *)sqlite3ErrName(rc));
 612     Tcl_AppendResult(interp, zBuf, sqlite3_errmsg(db), 0);
 613     return TCL_ERROR;
 614   }
 615
 616   if( pStmt ){
 617     if( sqlite3TestMakePointerStr(interp, zBuf, pStmt) ) return TCL_ERROR;
 618     Tcl_AppendResult(interp, zBuf, 0);
 619   }
 620   return TCL_OK;
 621 }
 622
 623 #endif /* SQLITE_OS_UNIX && SQLITE_ENABLE_UNLOCK_NOTIFY */
 624 /*
 625 ** End of implementation of [sqlite3_blocking_step].
 626 ************************************************************************/
 627
 628 /*
 629 ** Register commands with the TCL interpreter.
 630 */
 631 int SqlitetestThread_Init(Tcl_Interp *interp){
 632   Tcl_CreateObjCommand(interp, "sqlthread", sqlthread_proc, 0, 0);
 633   Tcl_CreateObjCommand(interp, "clock_seconds", clock_seconds_proc, 0, 0);
 634 #if SQLITE_OS_UNIX && defined(SQLITE_ENABLE_UNLOCK_NOTIFY)
 635   Tcl_CreateObjCommand(interp, "sqlite3_blocking_step", blocking_step_proc,0,0);
 636   Tcl_CreateObjCommand(interp,
 637       "sqlite3_blocking_prepare_v2", blocking_prepare_v2_proc, (void *)1, 0);
 638   Tcl_CreateObjCommand(interp,
 639       "sqlite3_nonblocking_prepare_v2", blocking_prepare_v2_proc, 0, 0);
 640 #endif
 641   return TCL_OK;
 642 }
 643 #else
 644 int SqlitetestThread_Init(Tcl_Interp *interp){
 645   return TCL_OK;
 646 }
 647 #endif