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Overview
Comment: | fix for locking in Windows (CVS 760) |
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Downloads: | Tarball | ZIP archive |
Timelines: | family | ancestors | descendants | both | trunk |
Files: | files | file ages | folders |
SHA1: |
83add34f64895a4b465881213eba82f3 |
User & Date: | mike 2002-10-17 00:38:54.000 |
Context
2002-10-17
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09:01 | Minor coding fix in getting the windows platform version, when multithreading (CVS 761) (check-in: b53ab71d07 user: mike tags: trunk) | |
00:38 | fix for locking in Windows (CVS 760) (check-in: 83add34f64 user: mike tags: trunk) | |
2002-10-12
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13:44 | Remove the call to srand() and add better comments to the sqliteOsRandomSeed() routine. Ticket #163. (CVS 759) (check-in: d87a886d8f user: drh tags: trunk) | |
Changes
Changes to src/os.c.
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488 489 490 491 492 493 494 | #endif #if OS_WIN DWORD got; SimulateIOError(SQLITE_IOERR); if( !ReadFile(id->h, pBuf, amt, &got, 0) ){ got = 0; } | | | 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 | #endif #if OS_WIN DWORD got; SimulateIOError(SQLITE_IOERR); if( !ReadFile(id->h, pBuf, amt, &got, 0) ){ got = 0; } if( (int)got==amt ){ return SQLITE_OK; }else{ return SQLITE_IOERR; } #endif } |
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622 623 624 625 626 627 628 629 630 631 632 | ** A lock is obtained on byte 0 before acquiring either a read lock or ** a write lock. This prevents two processes from attempting to get a ** lock at a same time. The semantics of sqliteOsReadLock() require that ** if there is already a write lock, that lock is converted into a read ** lock atomically. The lock on byte 0 allows us to drop the old write ** lock and get the read lock without another process jumping into the ** middle and messing us up. The same argument applies to sqliteOsWriteLock(). ** ** There are a finite number of read locks under windows. That number ** is determined by the following variable: */ | > > > > > | > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 | ** A lock is obtained on byte 0 before acquiring either a read lock or ** a write lock. This prevents two processes from attempting to get a ** lock at a same time. The semantics of sqliteOsReadLock() require that ** if there is already a write lock, that lock is converted into a read ** lock atomically. The lock on byte 0 allows us to drop the old write ** lock and get the read lock without another process jumping into the ** middle and messing us up. The same argument applies to sqliteOsWriteLock(). ** ** Locks must be obtained in an area that does not overlap the "real data area" ** otherwise read/write operations will conflict with lock operations. Locking beyond EOF ** is allowed in windows. ** ** There are a finite number of read locks under windows. That number ** is determined by the following variable: */ #define MX_LOCKBYTE 0xFFF0 #if OS_WIN // get the platform id to decide how to calculate the lock offset int mkPlatformId(void){ static long init=0; static int pid=VER_PLATFORM_WIN32_WINDOWS; OSVERSIONINFOA info; if (!init) { if (InterlockedIncrement(&init)==1) { info.dwOSVersionInfoSize=sizeof(info); if (GetVersionEx(&info)) pid=info.dwPlatformId; } } return pid; } // locks and unlocks beyond eof. uses platformid to move the lock as far as possible. int mklock(HANDLE h, WORD base, WORD size) { if (mkPlatformId()==VER_PLATFORM_WIN32_WINDOWS) return LockFile(h,0xFFFF0000+base,0,size,0); else return LockFile(h,base,0xFFFFFFFF,size,0); } int mkunlock(HANDLE h, WORD base, WORD size) { if (mkPlatformId()==VER_PLATFORM_WIN32_WINDOWS) return UnlockFile(h,0xFFFF0000+base,0,size,0); else return UnlockFile(h,base,0xFFFFFFFF,size,0); } //obtain the sync lock on a handle void synclock(HANDLE h){ while (!mklock(h,0,1)) Sleep(1); } void syncunlock(HANDLE h){ mkunlock(h,0,1); } #endif /* ** Change the status of the lock on the file "id" to be a readlock. ** If the file was write locked, then this reduces the lock to a read. ** If the file was read locked, then this acquires a new read lock. ** ** Return SQLITE_OK on success and SQLITE_BUSY on failure. */ int sqliteOsReadLock(OsFile *id){ #if OS_UNIX int rc; sqliteOsEnterMutex(); if( id->pLock->cnt>0 ){ if( !id->locked ){ id->pLock->cnt++; |
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670 671 672 673 674 675 676 | #if OS_WIN int rc; if( id->locked>0 ){ rc = SQLITE_OK; }else{ int lk = (sqliteRandomInteger() & 0x7ffffff)%MX_LOCKBYTE + 1; int res; | | | > | | | | 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 | #if OS_WIN int rc; if( id->locked>0 ){ rc = SQLITE_OK; }else{ int lk = (sqliteRandomInteger() & 0x7ffffff)%MX_LOCKBYTE + 1; int res; synclock(id->h); if (id->locked<0) mkunlock(id->h,1,MX_LOCKBYTE); // release write lock if we have it res=mklock(id->h,lk,1); syncunlock(id->h); if( res ){ id->locked = lk; rc = SQLITE_OK; }else{ rc = SQLITE_BUSY; } } |
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718 719 720 721 722 723 724 | #endif #if OS_WIN int rc; if( id->locked<0 ){ rc = SQLITE_OK; }else{ int res; | < < < < < | | > > > | | | 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 | #endif #if OS_WIN int rc; if( id->locked<0 ){ rc = SQLITE_OK; }else{ int res; synclock(id->h); if (id->locked>0) mkunlock(id->h,id->locked,1); // release read lock res=mklock(id->h,1,MX_LOCKBYTE); syncunlock(id->h); if(res){ id->locked = -1; rc = SQLITE_OK; }else{ rc = SQLITE_BUSY; } } return rc; |
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768 769 770 771 772 773 774 | } sqliteOsLeaveMutex(); id->locked = 0; return rc; #endif #if OS_WIN int rc; | < < | | < | < < < | > | | 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 | } sqliteOsLeaveMutex(); id->locked = 0; return rc; #endif #if OS_WIN int rc; if(id->locked<0 ) { mkunlock(id->h,1,MX_LOCKBYTE); }else if (id->locked>0) { mkunlock(id->h,id->locked,1); } id->locked = 0; return SQLITE_OK; #endif } /* ** Get information to seed the random number generator. The seed ** is written into the buffer zBuf[256]. The calling function must ** supply a sufficiently large buffer. |
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