/*

** 2007 August 28

**

** 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.

**

*************************************************************************

** This file contains the C functions that implement mutexes for pthreads

*/

#include "sqliteInt.h"

/*

** The code in this file is only used if we are compiling threadsafe

** under unix with pthreads.

**

** Note that this implementation requires a version of pthreads that

** supports recursive mutexes.

*/

#ifdef SQLITE_MUTEX_PTHREADS

#include <pthread.h>

/*

** The sqlite3_mutex.id, sqlite3_mutex.nRef, and sqlite3_mutex.owner fields

** are necessary under two condidtions: (1) Debug builds and (2) using

** home-grown mutexes. Encapsulate these conditions into a single #define.

*/

#if defined(SQLITE_DEBUG) || defined(SQLITE_HOMEGROWN_RECURSIVE_MUTEX)

# define SQLITE_MUTEX_NREF 1

#else

# define SQLITE_MUTEX_NREF 0

#endif

/*

** Each recursive mutex is an instance of the following structure.

*/

struct sqlite3_mutex {

pthread_mutex_t mutex; /* Mutex controlling the lock */

#if SQLITE_MUTEX_NREF || defined(SQLITE_ENABLE_API_ARMOR)

int id; /* Mutex type */

#endif

#if SQLITE_MUTEX_NREF

volatile int nRef; /* Number of entrances */

volatile pthread_t owner; /* Thread that is within this mutex */

int trace; /* True to trace changes */

#endif

};

#if SQLITE_MUTEX_NREF

# define SQLITE3_MUTEX_INITIALIZER(id) \

{PTHREAD_MUTEX_INITIALIZER,id,0,(pthread_t)0,0}

#elif defined(SQLITE_ENABLE_API_ARMOR)

# define SQLITE3_MUTEX_INITIALIZER(id) { PTHREAD_MUTEX_INITIALIZER, id }

#else

#define SQLITE3_MUTEX_INITIALIZER(id) { PTHREAD_MUTEX_INITIALIZER }

#endif

/*

** 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.

*/

#if !defined(NDEBUG) || defined(SQLITE_DEBUG)

static int pthreadMutexHeld(sqlite3_mutex *p){

return (p->nRef!=0 && pthread_equal(p->owner, pthread_self()));

}

static int pthreadMutexNotheld(sqlite3_mutex *p){

return p->nRef==0 || pthread_equal(p->owner, pthread_self())==0;

}

#endif

/*

** Try to provide a memory barrier operation, needed for initialization

** and also for the implementation of xShmBarrier in the VFS in cases

** where SQLite is compiled without mutexes.

*/

void sqlite3MemoryBarrier(void){

#if defined(SQLITE_MEMORY_BARRIER)

SQLITE_MEMORY_BARRIER;

#elif defined(__GNUC__) && GCC_VERSION>=4001000

__sync_synchronize();

#endif

}

/*

** Initialize and deinitialize the mutex subsystem.

*/

static int pthreadMutexInit(void){ return SQLITE_OK; }

static int pthreadMutexEnd(void){ return SQLITE_OK; }

/*

** 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:

**

** <ul>

** <li> SQLITE_MUTEX_FAST

** <li> SQLITE_MUTEX_RECURSIVE

** <li> SQLITE_MUTEX_STATIC_MASTER

** <li> SQLITE_MUTEX_STATIC_MEM

** <li> SQLITE_MUTEX_STATIC_OPEN

** <li> SQLITE_MUTEX_STATIC_PRNG

** <li> SQLITE_MUTEX_STATIC_LRU

** <li> SQLITE_MUTEX_STATIC_PMEM

** <li> SQLITE_MUTEX_STATIC_APP1

** <li> SQLITE_MUTEX_STATIC_APP2

** <li> SQLITE_MUTEX_STATIC_APP3

** <li> SQLITE_MUTEX_STATIC_VFS1

** <li> SQLITE_MUTEX_STATIC_VFS2

** <li> SQLITE_MUTEX_STATIC_VFS3

** </ul>

**

** The first two constants cause sqlite3_mutex_alloc() to create

** a new mutex. The new mutex is recursive when SQLITE_MUTEX_RECURSIVE

** is used but not necessarily so when SQLITE_MUTEX_FAST is used.

** The mutex implementation does not need to make a distinction

** 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. Six 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

** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()

** returns a different mutex on every call. But for the static

** mutex types, the same mutex is returned on every call that has

** the same type number.

*/

static sqlite3_mutex *pthreadMutexAlloc(int iType){

static sqlite3_mutex staticMutexes[] = {

SQLITE3_MUTEX_INITIALIZER(2),

SQLITE3_MUTEX_INITIALIZER(3),

SQLITE3_MUTEX_INITIALIZER(4),

SQLITE3_MUTEX_INITIALIZER(5),

SQLITE3_MUTEX_INITIALIZER(6),

SQLITE3_MUTEX_INITIALIZER(7),

SQLITE3_MUTEX_INITIALIZER(8),

SQLITE3_MUTEX_INITIALIZER(9),

SQLITE3_MUTEX_INITIALIZER(10),

SQLITE3_MUTEX_INITIALIZER(11),

SQLITE3_MUTEX_INITIALIZER(12),

SQLITE3_MUTEX_INITIALIZER(13)

};

sqlite3_mutex *p;

switch( iType ){

case SQLITE_MUTEX_RECURSIVE: {

p = sqlite3MallocZero( sizeof(*p) );

if( p ){

#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX

/* If recursive mutexes are not available, we will have to

** build our own. See below. */

pthread_mutex_init(&p->mutex, 0);

#else

/* Use a recursive mutex if it is available */

pthread_mutexattr_t recursiveAttr;

pthread_mutexattr_init(&recursiveAttr);

pthread_mutexattr_settype(&recursiveAttr, PTHREAD_MUTEX_RECURSIVE);

pthread_mutex_init(&p->mutex, &recursiveAttr);

pthread_mutexattr_destroy(&recursiveAttr);

#endif

#if SQLITE_MUTEX_NREF || defined(SQLITE_ENABLE_API_ARMOR)

p->id = SQLITE_MUTEX_RECURSIVE;

#endif

}

break;

}

case SQLITE_MUTEX_FAST: {

p = sqlite3MallocZero( sizeof(*p) );

if( p ){

pthread_mutex_init(&p->mutex, 0);

#if SQLITE_MUTEX_NREF || defined(SQLITE_ENABLE_API_ARMOR)

p->id = SQLITE_MUTEX_FAST;

#endif

}

break;

}

default: {

#ifdef SQLITE_ENABLE_API_ARMOR

if( iType-2<0 || iType-2>=ArraySize(staticMutexes) ){

(void)SQLITE_MISUSE_BKPT;

return 0;

}

#endif

p = &staticMutexes[iType-2];

break;

}

}

#if SQLITE_MUTEX_NREF || defined(SQLITE_ENABLE_API_ARMOR)

assert( p==0 || p->id==iType );

#endif

return p;

}

/*

** This routine deallocates a previously

** allocated mutex. SQLite is careful to deallocate every

** mutex that it allocates.

*/

static void pthreadMutexFree(sqlite3_mutex *p){

assert( p->nRef==0 );

#if SQLITE_ENABLE_API_ARMOR

if( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE )

#endif

{

pthread_mutex_destroy(&p->mutex);

sqlite3_free(p);

}

#ifdef SQLITE_ENABLE_API_ARMOR

else{

(void)SQLITE_MISUSE_BKPT;

}

#endif

}

/*

** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt

** to enter a mutex. If another thread is already within the mutex,

** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return

** SQLITE_BUSY. The sqlite3_mutex_try() interface returns SQLITE_OK

** 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.

*/

static void pthreadMutexEnter(sqlite3_mutex *p){

assert( p->id==SQLITE_MUTEX_RECURSIVE || pthreadMutexNotheld(p) );

#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX

/* If recursive mutexes are not available, then we have to grow

** our own. This implementation assumes that pthread_equal()

** is atomic - that it cannot be deceived into thinking self

** and p->owner are equal if p->owner changes between two values

** that are not equal to self while the comparison is taking place.

** This implementation also assumes a coherent cache - that

** separate processes cannot read different values from the same

** address at the same time. If either of these two conditions

** are not met, then the mutexes will fail and problems will result.

*/

{

pthread_t self = pthread_self();

if( p->nRef>0 && pthread_equal(p->owner, self) ){

p->nRef++;

}else{

pthread_mutex_lock(&p->mutex);

assert( p->nRef==0 );

p->owner = self;

p->nRef = 1;

}

}

#else

/* Use the built-in recursive mutexes if they are available.

*/

pthread_mutex_lock(&p->mutex);

#if SQLITE_MUTEX_NREF

assert( p->nRef>0 || p->owner==0 );

p->owner = pthread_self();

p->nRef++;

#endif

#endif

#ifdef SQLITE_DEBUG

if( p->trace ){

printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);

}

#endif

}

static int pthreadMutexTry(sqlite3_mutex *p){

int rc;

assert( p->id==SQLITE_MUTEX_RECURSIVE || pthreadMutexNotheld(p) );

#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX

/* If recursive mutexes are not available, then we have to grow

** our own. This implementation assumes that pthread_equal()

** is atomic - that it cannot be deceived into thinking self

** and p->owner are equal if p->owner changes between two values

** that are not equal to self while the comparison is taking place.

** This implementation also assumes a coherent cache - that

** separate processes cannot read different values from the same

** address at the same time. If either of these two conditions

** are not met, then the mutexes will fail and problems will result.

*/

{

pthread_t self = pthread_self();

if( p->nRef>0 && pthread_equal(p->owner, self) ){

p->nRef++;

rc = SQLITE_OK;

}else if( pthread_mutex_trylock(&p->mutex)==0 ){

assert( p->nRef==0 );

p->owner = self;

p->nRef = 1;

rc = SQLITE_OK;

}else{

rc = SQLITE_BUSY;

}

}

#else

/* Use the built-in recursive mutexes if they are available.

*/

if( pthread_mutex_trylock(&p->mutex)==0 ){

#if SQLITE_MUTEX_NREF

p->owner = pthread_self();

p->nRef++;

#endif

rc = SQLITE_OK;

}else{

rc = SQLITE_BUSY;

}

#endif

#ifdef SQLITE_DEBUG

if( rc==SQLITE_OK && p->trace ){

printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);

}

#endif

return rc;

}

/*

** 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.

*/

static void pthreadMutexLeave(sqlite3_mutex *p){

assert( pthreadMutexHeld(p) );

#if SQLITE_MUTEX_NREF

p->nRef--;

if( p->nRef==0 ) p->owner = 0;

#endif

assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );

#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX

if( p->nRef==0 ){

pthread_mutex_unlock(&p->mutex);

}

#else

pthread_mutex_unlock(&p->mutex);

#endif

#ifdef SQLITE_DEBUG

if( p->trace ){

printf("leave mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);

}

#endif

}

sqlite3_mutex_methods const *sqlite3DefaultMutex(void){

static const sqlite3_mutex_methods sMutex = {

pthreadMutexInit,

pthreadMutexEnd,

pthreadMutexAlloc,

pthreadMutexFree,

pthreadMutexEnter,

pthreadMutexTry,

pthreadMutexLeave,

#ifdef SQLITE_DEBUG

pthreadMutexHeld,

pthreadMutexNotheld

#else

0,

0

#endif

};

return &sMutex;

}

#endif /* SQLITE_MUTEX_PTHREADS */