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In wal.c: improved comments, new assert() and testcase() macros, and

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replace some magic numbers with appropriate symbolic constants.

FossilOrigin-Name: 13ec8a77a47aa471af587459f4094da0d06674c5960f0d34777bcb3d38bc413b
This commit is contained in:
drh
2017-11-11 20:11:01 +00:00
parent 870655bb9e
commit c05a063c68
3 changed files with 30 additions and 17 deletions
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33
src/wal.c
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@@ -545,6 +545,11 @@ struct WalIterator {
** is broken into pages of WALINDEX_PGSZ bytes. Wal-index pages are
** numbered from zero.
**
** If the wal-index is currently smaller the iPage pages then the size
** of the wal-index might be increased, but only if it is safe to do
** so. It is safe to enlarge the wal-index if pWal->writeLock is true
** or pWal->exclusiveMode==WAL_HEAPMEMORY_MODE.
**
** If this call is successful, *ppPage is set to point to the wal-index
** page and SQLITE_OK is returned. If an error (an OOM or VFS error) occurs,
** then an SQLite error code is returned and *ppPage is set to 0.
@@ -576,6 +581,8 @@ static int walIndexPage(Wal *pWal, int iPage, volatile u32 **ppPage){
rc = sqlite3OsShmMap(pWal->pDbFd, iPage, WALINDEX_PGSZ,
pWal->writeLock, (void volatile **)&pWal->apWiData[iPage]
);
assert( pWal->apWiData[iPage]!=0 || rc!=SQLITE_OK || pWal->writeLock==0 );
testcase( pWal->apWiData[iPage]==0 && rc==SQLITE_OK );
if( (rc&0xff)==SQLITE_READONLY ){
pWal->readOnly |= WAL_SHM_RDONLY;
if( rc==SQLITE_READONLY ){
@@ -2108,15 +2115,21 @@ static int walIndexReadHdr(Wal *pWal, int *pChanged){
** open, and hence the content of the shared-memory is unreliable,
** since the shared-memory might be inconsistent with the WAL file
** and there is no writer on hand to fix it. */
assert( page0==0 && pWal->writeLock==0 );
assert( page0==0 );
assert( pWal->writeLock==0 );
assert( pWal->readOnly & WAL_SHM_RDONLY );
pWal->bShmUnreliable = 1;
pWal->exclusiveMode = WAL_HEAPMEMORY_MODE;
*pChanged = 1;
}else{
return rc; /* Any other non-OK return is just an error */
}
};
assert( page0 || pWal->writeLock==0 );
}else{
/* page0 can be NULL if the SHM is zero bytes in size and pWal->writeLock
** is zero, which prevents the SHM from growing */
testcase( page0!=0 );
}
assert( page0!=0 || pWal->writeLock==0 );
/* If the first page of the wal-index has been mapped, try to read the
** wal-index header immediately, without holding any lock. This usually
@@ -3661,24 +3674,24 @@ int sqlite3WalExclusiveMode(Wal *pWal, int op){
assert( pWal->readLock>=0 || (op<=0 && pWal->exclusiveMode==0) );
if( op==0 ){
if( pWal->exclusiveMode ){
pWal->exclusiveMode = 0;
if( pWal->exclusiveMode!=WAL_NORMAL_MODE ){
pWal->exclusiveMode = WAL_NORMAL_MODE;
if( walLockShared(pWal, WAL_READ_LOCK(pWal->readLock))!=SQLITE_OK ){
pWal->exclusiveMode = 1;
pWal->exclusiveMode = WAL_EXCLUSIVE_MODE;
}
rc = pWal->exclusiveMode==0;
rc = pWal->exclusiveMode==WAL_NORMAL_MODE;
}else{
/* Already in locking_mode=NORMAL */
rc = 0;
}
}else if( op>0 ){
assert( pWal->exclusiveMode==0 );
assert( pWal->exclusiveMode==WAL_NORMAL_MODE );
assert( pWal->readLock>=0 );
walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock));
pWal->exclusiveMode = 1;
pWal->exclusiveMode = WAL_EXCLUSIVE_MODE;
rc = 1;
}else{
rc = pWal->exclusiveMode==0;
rc = pWal->exclusiveMode==WAL_NORMAL_MODE;
}
return rc;
}