dvander@1645: /*
dvander@1645: ** 2007 August 14
dvander@1645: **
dvander@1645: ** The author disclaims copyright to this source code.  In place of
dvander@1645: ** a legal notice, here is a blessing:
dvander@1645: **
dvander@1645: **    May you do good and not evil.
dvander@1645: **    May you find forgiveness for yourself and forgive others.
dvander@1645: **    May you share freely, never taking more than you give.
dvander@1645: **
dvander@1645: *************************************************************************
dvander@1645: ** This file contains the C functions that implement mutexes.
dvander@1645: **
dvander@1645: ** The implementation in this file does not provide any mutual
dvander@1645: ** exclusion and is thus suitable for use only in applications
dvander@1645: ** that use SQLite in a single thread.  But this implementation
dvander@1645: ** does do a lot of error checking on mutexes to make sure they
dvander@1645: ** are called correctly and at appropriate times.  Hence, this
dvander@1645: ** implementation is suitable for testing.
dvander@1645: ** debugging purposes
dvander@1645: **
dvander@1645: ** $Id$
dvander@1645: */
dvander@1645: #include "sqliteInt.h"
dvander@1645: 
dvander@1645: #ifdef SQLITE_MUTEX_NOOP_DEBUG
dvander@1645: /*
dvander@1645: ** In this implementation, mutexes do not provide any mutual exclusion.
dvander@1645: ** But the error checking is provided.  This implementation is useful
dvander@1645: ** for test purposes.
dvander@1645: */
dvander@1645: 
dvander@1645: /*
dvander@1645: ** The mutex object
dvander@1645: */
dvander@1645: struct sqlite3_mutex {
dvander@1645:   int id;     /* The mutex type */
dvander@1645:   int cnt;    /* Number of entries without a matching leave */
dvander@1645: };
dvander@1645: 
dvander@1645: /*
dvander@1645: ** The sqlite3_mutex_alloc() routine allocates a new
dvander@1645: ** mutex and returns a pointer to it.  If it returns NULL
dvander@1645: ** that means that a mutex could not be allocated. 
dvander@1645: */
dvander@1645: sqlite3_mutex *sqlite3_mutex_alloc(int id){
dvander@1645:   static sqlite3_mutex aStatic[5];
dvander@1645:   sqlite3_mutex *pNew = 0;
dvander@1645:   switch( id ){
dvander@1645:     case SQLITE_MUTEX_FAST:
dvander@1645:     case SQLITE_MUTEX_RECURSIVE: {
dvander@1645:       pNew = sqlite3_malloc(sizeof(*pNew));
dvander@1645:       if( pNew ){
dvander@1645:         pNew->id = id;
dvander@1645:         pNew->cnt = 0;
dvander@1645:       }
dvander@1645:       break;
dvander@1645:     }
dvander@1645:     default: {
dvander@1645:       assert( id-2 >= 0 );
dvander@1645:       assert( id-2 < sizeof(aStatic)/sizeof(aStatic[0]) );
dvander@1645:       pNew = &aStatic[id-2];
dvander@1645:       pNew->id = id;
dvander@1645:       break;
dvander@1645:     }
dvander@1645:   }
dvander@1645:   return pNew;
dvander@1645: }
dvander@1645: 
dvander@1645: /*
dvander@1645: ** This routine deallocates a previously allocated mutex.
dvander@1645: */
dvander@1645: void sqlite3_mutex_free(sqlite3_mutex *p){
dvander@1645:   assert( p );
dvander@1645:   assert( p->cnt==0 );
dvander@1645:   assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );
dvander@1645:   sqlite3_free(p);
dvander@1645: }
dvander@1645: 
dvander@1645: /*
dvander@1645: ** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
dvander@1645: ** to enter a mutex.  If another thread is already within the mutex,
dvander@1645: ** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
dvander@1645: ** SQLITE_BUSY.  The sqlite3_mutex_try() interface returns SQLITE_OK
dvander@1645: ** upon successful entry.  Mutexes created using SQLITE_MUTEX_RECURSIVE can
dvander@1645: ** be entered multiple times by the same thread.  In such cases the,
dvander@1645: ** mutex must be exited an equal number of times before another thread
dvander@1645: ** can enter.  If the same thread tries to enter any other kind of mutex
dvander@1645: ** more than once, the behavior is undefined.
dvander@1645: */
dvander@1645: void sqlite3_mutex_enter(sqlite3_mutex *p){
dvander@1645:   assert( p );
dvander@1645:   assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
dvander@1645:   p->cnt++;
dvander@1645: }
dvander@1645: int sqlite3_mutex_try(sqlite3_mutex *p){
dvander@1645:   assert( p );
dvander@1645:   assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
dvander@1645:   p->cnt++;
dvander@1645:   return SQLITE_OK;
dvander@1645: }
dvander@1645: 
dvander@1645: /*
dvander@1645: ** The sqlite3_mutex_leave() routine exits a mutex that was
dvander@1645: ** previously entered by the same thread.  The behavior
dvander@1645: ** is undefined if the mutex is not currently entered or
dvander@1645: ** is not currently allocated.  SQLite will never do either.
dvander@1645: */
dvander@1645: void sqlite3_mutex_leave(sqlite3_mutex *p){
dvander@1645:   assert( p );
dvander@1645:   assert( sqlite3_mutex_held(p) );
dvander@1645:   p->cnt--;
dvander@1645:   assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
dvander@1645: }
dvander@1645: 
dvander@1645: /*
dvander@1645: ** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
dvander@1645: ** intended for use inside assert() statements.
dvander@1645: */
dvander@1645: int sqlite3_mutex_held(sqlite3_mutex *p){
dvander@1645:   return p==0 || p->cnt>0;
dvander@1645: }
dvander@1645: int sqlite3_mutex_notheld(sqlite3_mutex *p){
dvander@1645:   return p==0 || p->cnt==0;
dvander@1645: }
dvander@1645: #endif /* SQLITE_MUTEX_NOOP_DEBUG */