SQLite

**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains the C functions that implement mutexes for
** use by the SQLite core.
**
** $Id: mutex.c,v 1.12 2007/08/25 16:21:30 drh Exp $
*/
/*
** If SQLITE_MUTEX_APPDEF is defined, then this whole module is
** omitted and equivalent functionality must be provided by the
** application that links against the SQLite library.
*/
#ifndef SQLITE_MUTEX_APPDEF


/* This is the beginning of internal implementation of mutexes
** for SQLite.
*/
#include "sqliteInt.h"

/*
** Figure out what version of the code to use.  The choices are
**
**   SQLITE_MUTEX_NOOP         For single-threaded applications that
**                             do not desire error checking.
**
**   SQLITE_MUTEX_NOOP_DEBUG   For single-threaded applications with
**                             error checking to help verify that mutexes
**                             are being used correctly even though they
**                             are not needed.  Used when SQLITE_DEBUG is
**                             defined on single-threaded builds.
**
**   SQLITE_MUTEX_PTHREADS     For multi-threaded applications on Unix.
**
**   SQLITE_MUTEX_WIN          For multi-threaded applications on Win32.
*/
#define SQLITE_MUTEX_NOOP 1   /* The default */
#if defined(SQLITE_DEBUG) && !SQLITE_THREADSAFE
# undef SQLITE_MUTEX_NOOP
# define SQLITE_MUTEX_NOOP_DEBUG
#endif
#if defined(SQLITE_MUTEX_NOOP) && SQLITE_THREADSAFE && OS_UNIX

** for test purposes.
*/

/*
** The mutex object
*/
struct sqlite3_mutex {
  int id;     /* The mutex type */
  int cnt;    /* Number of entries without a matching leave */
};

/*
** The sqlite3_mutex_alloc() routine allocates a new
** mutex and returns a pointer to it.  If it returns NULL
** that means that a mutex could not be allocated. 
*/

** be entered multiple times by the same thread.  In such cases the,
** mutex must be exited an equal number of times before another thread
** can enter.  If the same thread tries to enter any other kind of mutex
** more than once, the behavior is undefined.
*/
void sqlite3_mutex_enter(sqlite3_mutex *p){
  assert( p );
  assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
  p->cnt++;
}
int sqlite3_mutex_try(sqlite3_mutex *p){
  assert( p );
  assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );


  p->cnt++;
  return SQLITE_OK;
}

/*
** The sqlite3_mutex_leave() routine exits a mutex that was
** previously entered by the same thread.  The behavior
** is undefined if the mutex is not currently entered or
** is not currently allocated.  SQLite will never do either.
*/
void sqlite3_mutex_leave(sqlite3_mutex *p){
  assert( p );
  assert( sqlite3_mutex_held(p) );
  p->cnt--;
  assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
}

/*
** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
** intended for use inside assert() statements.
*/
int sqlite3_mutex_held(sqlite3_mutex *p){

** is undefined if the mutex is not currently entered or
** is not currently allocated.  SQLite will never do either.
*/
void sqlite3_mutex_leave(sqlite3_mutex *p){
  assert( p );
  assert( sqlite3_mutex_held(p) );
  p->nRef--;
  assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );
  pthread_mutex_unlock(&p->mutex);
}

/*
** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
** intended for use only inside assert() statements.  On some platforms,
** there might be race conditions that can cause these routines to
** deliver incorrect results.  In particular, if pthread_equal() is
** not an atomic operation, then these routines might delivery
** incorrect results.  On most platforms, pthread_equal() is a 
** comparison of two integers and is therefore atomic.  But we are
** told that HPUX is not such a platform.  If so, then these routines
** will not always work correctly on HPUX.
**
** On those platforms where pthread_equal() is not atomic, SQLite
** should be compiled without -DSQLITE_DEBUG and with -DNDEBUG to
** make sure no assert() statements are evaluated and hence these
** routines are never called.
*/
#ifndef NDEBUG
int sqlite3_mutex_held(sqlite3_mutex *p){
  return p==0 || (p->nRef!=0 && pthread_equal(p->owner, pthread_self()));
}
int sqlite3_mutex_notheld(sqlite3_mutex *p){
  return p==0 || p->nRef==0 || pthread_equal(p->owner, pthread_self())==0;
}
#endif
#endif /* SQLITE_MUTEX_PTHREAD */

#ifdef SQLITE_MUTEX_WIN
/********************** Windows Mutex Implementation **********************
**
** This implementation of mutexes is built using the win32 API.
*/

** is undefined if the mutex is not currently entered or
** is not currently allocated.  SQLite will never do either.
*/
void sqlite3_mutex_leave(sqlite3_mutex *p){
  assert( p->nRef>0 );
  assert( p->owner==GetCurrentThreadId() );
  p->nRef--;
  assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );
  LeaveCriticalSection(&p->mutex);
}

/*
** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
** intended for use only inside assert() statements.
*/
int sqlite3_mutex_held(sqlite3_mutex *p){
  return p==0 || (p->nRef!=0 && p->owner==GetCurrentThreadId());
}
int sqlite3_mutex_notheld(sqlite3_mutex *p){
  return p==0 || p->nRef==0 || p->owner!=GetCurrentThreadId();
}
#endif /* SQLITE_MUTEX_WIN */

#endif /* !defined(SQLITE_MUTEX_APPDEF) */

** on how SQLite interfaces are suppose to operate.
**
** The name of this file under configuration management is "sqlite.h.in".
** The makefile makes some minor changes to this file (such as inserting
** the version number) and changes its name to "sqlite3.h" as
** part of the build process.
**
** @(#) $Id: sqlite.h.in,v 1.242 2007/08/25 16:21:30 drh Exp $
*/
#ifndef _SQLITE3_H_
#define _SQLITE3_H_
#include <stdarg.h>     /* Needed for the definition of va_list */

/*
** Make sure we can call this stuff from C++.

int sqlite3_libversion_number(void);

/*
** CAPI3REF: Database Connection Handle
**
** Each open SQLite database is represented by pointer to an instance of the
** opaque structure named "sqlite3".  It is useful to think of an sqlite3
** pointer as an object.  The [sqlite3_open()], [sqlite3_open16()], and
** [sqlite3_open_v2()] interfaces are its constructors
** and [sqlite3_close()] is its destructor.  There are many other interfaces
** (such as [sqlite3_prepare_v2()], [sqlite3_create_function()], and
** [sqlite3_busy_timeout()] to name but three) that are methods on this
** object.
*/
typedef struct sqlite3 sqlite3;


/*
** CAPI3REF: 64-Bit Integer Types

** Instead of invoking a user-supplied callback for each row of the
** result, this routine remembers each row of the result in memory
** obtained from [sqlite3_malloc()], then returns all of the result after the
** query has finished. 
**
** As an example, suppose the query result where this table:
**
** <blockquote><pre>
**        Name        | Age
**        -----------------------
**        Alice       | 43
**        Bob         | 28
**        Cindy       | 21
** </pre></blockquote>
**
** If the 3rd argument were &azResult then after the function returns
** azResult will contain the following data:
**
** <blockquote><pre>
**        azResult&#91;0] = "Name";
**        azResult&#91;1] = "Age";
**        azResult&#91;2] = "Alice";
**        azResult&#91;3] = "43";
**        azResult&#91;4] = "Bob";
**        azResult&#91;5] = "28";
**        azResult&#91;6] = "Cindy";
**        azResult&#91;7] = "21";
** </pre></blockquote>
**
** Notice that there is an extra row of data containing the column
** headers.  But the *nrow return value is still 3.  *ncolumn is
** set to 2.  In general, the number of values inserted into azResult
** will be ((*nrow) + 1)*(*ncolumn).
**
** After the calling function has finished using the result, it should 

char *sqlite3_vmprintf(const char*, va_list);
char *sqlite3_snprintf(int,char*,const char*, ...);

/*
** CAPI3REF: Memory Allocation Subsystem
**
** The SQLite core uses these three routines for all of its own
** internal memory allocation needs. The default implementation
** of the memory allocation subsystem uses the malloc(), realloc()
** and free() provided by the standard C library.  However, if 
** SQLite is compiled with the following C preprocessor macro
**
** <blockquote> SQLITE_OMIT_MEMORY_ALLOCATION </blockquote>
**
** then no implementation is provided for these routines by
** SQLite.  The application that links against SQLite is
** expected to provide its own implementation.  If the application
** does provide its own implementation for these routines, then
** it must also provide an implementation for
** [sqlite3_memory_alarm()].
**
** <b>Exception:</b> The windows OS interface layer calls
** the system malloc() and free() directly when converting
** filenames between the UTF-8 encoding used by SQLite
** and whatever filename encoding is used by the particular windows
** installation.  Memory allocation errors are detected, but
** they are reported back as [SQLITE_CANTOPEN] or
** [SQLITE_IOERR] rather than [SQLITE_NOMEM].
*/
void *sqlite3_malloc(int);
void *sqlite3_realloc(void*, int);
void sqlite3_free(void*);

/*
** CAPI3REF: Memory Allocator Statistics

** the recursive calls.
**
** The [sqlite3_soft_heap_limit()] interface works by registering
** a memory alarm at the soft heap limit and invoking 
** [sqlite3_release_memory()] in the alarm callback.  Application
** programs should not attempt to use the [sqlite3_memory_alarm()]
** interface because doing so will interfere with the
** [sqlite3_soft_heap_limit()] module.  This interface is exposed
** only so that applications can provide their own
** alternative implementation when the SQLite core is
** compiled with SQLITE_OMIT_MEMORY_ALLOCATION.
*/
int sqlite3_memory_alarm(
  void(*xCallback)(void *pArg, sqlite3_int64 used, int N),
  void *pArg,
  sqlite3_int64 iThreshold
);

** if the same host parameter name is used multiple times, each occurrance
** is given the same number, so the value returned in that case is the number
** of unique host parameter names.  If host parameters of the form "?NNN"
** are used (where NNN is an integer) then there might be gaps in the
** numbering and the value returned by this interface is the index of the
** host parameter with the largest index value.
**
** The prepared statement must not be [sqlite3_finalize | finalized]
** prior to this routine returnning.  Otherwise the results are undefined
** and probably undesirable.
*/
int sqlite3_bind_parameter_count(sqlite3_stmt*);

/*
** CAPI3REF: Name Of A Host Parameter

** example, if the internal representation is FLOAT and a text result
** is requested, [sqlite3_snprintf()] is used internally to do the conversion
** automatically.  The following table details the conversions that
** are applied:
**
** <blockquote>
** <table border="1">
** <tr><th> Internal<br>Type <th> Requested<br>Type <th>  Conversion

**
** <tr><td>  NULL    <td> INTEGER   <td> Result is 0
** <tr><td>  NULL    <td>  FLOAT    <td> Result is 0.0
** <tr><td>  NULL    <td>   TEXT    <td> Result is NULL pointer
** <tr><td>  NULL    <td>   BLOB    <td> Result is NULL pointer
** <tr><td> INTEGER  <td>  FLOAT    <td> Convert from integer to float
** <tr><td> INTEGER  <td>   TEXT    <td> ASCII rendering of the integer

** This function causes the current thread to suspend execution
** a number of milliseconds specified in its parameter.
**
** If the operating system does not support sleep requests with 
** millisecond time resolution, then the time will be rounded up to 
** the nearest second. The number of milliseconds of sleep actually 
** requested from the operating system is returned.
**
** SQLite implements this interface by calling the xSleep()
** method of the default [sqlite3_vfs] object.
*/
int sqlite3_sleep(int);

/*
** CAPI3REF:  Name Of The Folder Holding Temporary Files
**
** If this global variable is made to point to a string which is

** implementation.  This means that if the application also uses the
** memory alarm interface it will interfere with the operation of the
** soft heap limit and undefined behavior will result.  
**
** Prior to SQLite version 3.5.0, this routine only constrained the memory
** allocated by a single thread - the same thread in which this routine
** runs.  Beginning with SQLite version 3.5.0, the soft heap limit is
** applied to all threads.  The value specified for the soft heap limit
** is an bound on the total memory allocation for all threads.  In
** version 3.5.0 there is no mechanism for limiting the heap usage for
** individual threads.
*/
void sqlite3_soft_heap_limit(int);

/*
** CAPI3REF:  Extract Metadata About A Column Of A Table
**
** This routine

**
** The SQLite core uses these routines for thread
** synchronization.  Though they are intended for internal
** use by SQLite, code that links against SQLite is
** permitted to use any of these routines.
**
** The SQLite source code contains multiple implementations 
** of these mutex routines.  An appropriate implementation
** is selected automatically at compile-time.  The following
** implementations are available in the SQLite core:
**
** <ul>
** <li>   SQLITE_MUTEX_PTHREAD
** <li>   SQLITE_MUTEX_WIN
** <li>   SQLITE_MUTEX_NOOP

** </ul>
**



** The SQLITE_MUTEX_NOOP implementation is a set of routines 
** that does no real locking and is appropriate for use in 
** a single-threaded application.  The SQLITE_MUTEX_PTHREAD
** and SQLITE_MUTEX_WIN implementations are appropriate for
** use on unix and windows.
** 
** If SQLite is compiled with the SQLITE_MUTEX_APPDEF preprocessor
** macro defined (with "-DSQLITE_MUTEX_APPDEF=1"), then no mutex
** implementation is included with the library.  The
** mutex interface routines defined here become external
** references in the SQLite library for which implementations
** must be provided by the application.  This facility allows an
** application that links against SQLite to provide its own mutex
** implementation without having to modify the SQLite core.
**
** The sqlite3_mutex_alloc() routine allocates a new
** mutex and returns a pointer to it.  If it returns NULL
** that means that a mutex could not be allocated.  SQLite
** will unwind its stack and return an error.  The argument
** to sqlite3_mutex_alloc() is one of these integer constants:
**

** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
** not want to.  But SQLite will only request a recursive mutex in
** cases where it really needs one.  If a faster non-recursive mutex
** implementation is available on the host platform, the mutex subsystem
** might return such a mutex in response to SQLITE_MUTEX_FAST.
**
** The other allowed parameters to sqlite3_mutex_alloc() each return
** a pointer to a static preexisting mutex.  Four static mutexes are
** used by the current version of SQLite.  Future versions of SQLite
** may add additional static mutexes.  Static mutexes are for internal
** use by SQLite only.  Applications that use SQLite mutexes should
** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
** SQLITE_MUTEX_RECURSIVE.
**
** Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST

** upon successful entry.  Mutexes created using SQLITE_MUTEX_RECURSIVE can
** be entered multiple times by the same thread.  In such cases the,
** mutex must be exited an equal number of times before another thread
** can enter.  If the same thread tries to enter any other kind of mutex
** more than once, the behavior is undefined.   SQLite will never exhibit
** such behavior in its own use of mutexes.
**
** The sqlite3_mutex_leave() routine exits a mutex that was
** previously entered by the same thread.  The behavior
** is undefined if the mutex is not currently entered by the
** calling thread or is not currently allocated.  SQLite will
** never do either.
**
** See also: [sqlite3_mutex_held()] and [sqlite3_mutex_notheld()].
*/
sqlite3_mutex *sqlite3_mutex_alloc(int);
void sqlite3_mutex_free(sqlite3_mutex*);
void sqlite3_mutex_enter(sqlite3_mutex*);
int sqlite3_mutex_try(sqlite3_mutex*);
void sqlite3_mutex_leave(sqlite3_mutex*);

/*
** CAPI3REF: Mutex Verifcation Routines
**
** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routines
** are intended for use inside assert() statements.  The SQLite core
** never uses these routines except inside an assert() and applications
** are advised to follow the lead of the core.  The core only
** provides implementations for these routines when it is compiled
** with the SQLITE_DEBUG flag.  External mutex implementations
** are only required to provide these routines if SQLITE_DEBUG is
** defined and if NDEBUG is not defined.
**
** These routines should return true if the mutex in their argument
** is held or not held, respectively, by the calling thread.
**
** The implementation is not required to provided versions of these
** routines that actually work.
** If the implementation does not provide working
** versions of these routines, it should at least provide stubs
** that always return true so that one does not get spurious
** assertion failures.
**
** If the argument to sqlite3_mutex_held() is a NULL pointer then
** the routine should return 1.  This seems counter-intuitive since
** clearly the mutex cannot be held if it does not exist.  But the
** the reason the mutex does not exist is because the build is not
** using mutexes.  And we do not want the assert() containing the
** call to sqlite3_mutex_held() to fail, so a non-zero return is
** the appropriate thing to do.  The sqlite3_mutex_notheld() 
** interface should also return 1 when given a NULL pointer.
*/





int sqlite3_mutex_held(sqlite3_mutex*);
int sqlite3_mutex_notheld(sqlite3_mutex*);

/*
** CAPI3REF: Mutex Types
**
** The [sqlite3_mutex_alloc()] interface takes a single argument