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/*
** 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 OS/2
**
** $Id: mutex_os2.c,v 1.3 2007/10/02 19:56:04 pweilbacher Exp $
*/
#include "sqliteInt.h"
/*
** The code in this file is only used if SQLITE_MUTEX_OS2 is defined.
** See the mutex.h file for details.
*/
#ifdef SQLITE_MUTEX_OS2
/********************** OS/2 Mutex Implementation **********************
**
** This implementation of mutexes is built using the OS/2 API.
*/
/*
** The mutex object
** Each recursive mutex is an instance of the following structure.
*/
struct sqlite3_mutex {
PSZ mutexName; /* Mutex name controlling the lock */
HMTX mutex; /* Mutex controlling the lock */
int id; /* Mutex type */
int nRef; /* Number of references */
TID owner; /* Thread holding this mutex */
};
/*
** 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 0
** <li> SQLITE_MUTEX_RECURSIVE 1
** <li> SQLITE_MUTEX_STATIC_MASTER 2
** <li> SQLITE_MUTEX_STATIC_MEM 3
** <li> SQLITE_MUTEX_STATIC_PRNG 4
** </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. Three 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.
*/
sqlite3_mutex *sqlite3_mutex_alloc(int iType){
PSZ mutex_name = "\\SEM32\\SQLITE\\MUTEX";
int mutex_name_len = strlen(mutex_name) + 1; /* name length + null byte */
sqlite3_mutex *p;
switch( iType ){
case SQLITE_MUTEX_FAST:
case SQLITE_MUTEX_RECURSIVE: {
p = sqlite3MallocZero( sizeof(*p) );
if( p ){
p->mutexName = (PSZ)malloc(mutex_name_len);
sqlite3_snprintf(mutex_name_len, p->mutexName, "%s", mutex_name);
p->id = iType;
DosCreateMutexSem(p->mutexName, &p->mutex, 0, FALSE);
DosOpenMutexSem(p->mutexName, &p->mutex);
}
break;
}
default: {
static sqlite3_mutex staticMutexes[5];
static int isInit = 0;
while( !isInit ) {
static long lock = 0;
DosEnterCritSec();
lock++;
if( lock == 1 ) {
DosExitCritSec();
int i;
for(i = 0; i < sizeof(staticMutexes)/sizeof(staticMutexes[0]); i++) {
staticMutexes[i].mutexName = (PSZ)malloc(mutex_name_len + 1);
sqlite3_snprintf(mutex_name_len + 1, /* one more for the number */
staticMutexes[i].mutexName, "%s%1d", mutex_name, i);
DosCreateMutexSem(staticMutexes[i].mutexName,
&staticMutexes[i].mutex, 0, FALSE);
DosOpenMutexSem(staticMutexes[i].mutexName,
&staticMutexes[i].mutex);
}
isInit = 1;
} else {
DosExitCritSec();
DosSleep(1);
}
}
assert( iType-2 >= 0 );
assert( iType-2 < sizeof(staticMutexes)/sizeof(staticMutexes[0]) );
p = &staticMutexes[iType-2];
p->id = iType;
break;
}
}
return p;
}
/*
** This routine deallocates a previously allocated mutex.
** SQLite is careful to deallocate every mutex that it allocates.
*/
void sqlite3_mutex_free(sqlite3_mutex *p){
assert( p );
assert( p->nRef==0 );
assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );
DosCloseMutexSem(p->mutex);
free(p->mutexName);
sqlite3_free(p);
}
/*
** 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.
*/
void sqlite3_mutex_enter(sqlite3_mutex *p){
TID tid;
PID holder1;
ULONG holder2;
assert( p );
assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
DosRequestMutexSem(p->mutex, SEM_INDEFINITE_WAIT);
DosQueryMutexSem(p->mutex, &holder1, &tid, &holder2);
p->owner = tid;
p->nRef++;
}
int sqlite3_mutex_try(sqlite3_mutex *p){
int rc;
TID tid;
PID holder1;
ULONG holder2;
assert( p );
assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
if( DosRequestMutexSem(p->mutex, SEM_IMMEDIATE_RETURN) == NO_ERROR) {
DosQueryMutexSem(p->mutex, &holder1, &tid, &holder2);
p->owner = tid;
p->nRef++;
rc = SQLITE_OK;
} else {
rc = SQLITE_BUSY;
}
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.
*/
void sqlite3_mutex_leave(sqlite3_mutex *p){
TID tid;
PID holder1;
ULONG holder2;
assert( p->nRef>0 );
DosQueryMutexSem(p->mutex, &holder1, &tid, &holder2);
assert( p->owner==tid );
p->nRef--;
assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );
DosReleaseMutexSem(p->mutex);
}
/*
** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
** intended for use inside assert() statements.
*/
int sqlite3_mutex_held(sqlite3_mutex *p){
TID tid;
PID pid;
ULONG ulCount;
PTIB ptib;
if( p!=0 ) {
DosQueryMutexSem(p->mutex, &pid, &tid, &ulCount);
} else {
DosGetInfoBlocks(&ptib, NULL);
tid = ptib->tib_ptib2->tib2_ultid;
}
return p==0 || (p->nRef!=0 && p->owner==tid);
}
int sqlite3_mutex_notheld(sqlite3_mutex *p){
TID tid;
PID pid;
ULONG ulCount;
PTIB ptib;
if( p!= 0 ) {
DosQueryMutexSem(p->mutex, &pid, &tid, &ulCount);
} else {
DosGetInfoBlocks(&ptib, NULL);
tid = ptib->tib_ptib2->tib2_ultid;
}
return p==0 || p->nRef==0 || p->owner!=tid;
}
#endif /* SQLITE_MUTEX_OS2 */
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