Modify the hasHotJournal() routine to return a false-positive if it is

unable to open the journal file to check its header due to a race
condition.  Processing downstream of hasHotJournal() already knows how to
deal with false-positives.  Ticket #3883. (CVS 6687)

FossilOrigin-Name: d6b5d8e1ab8e5d3348ace560230702718a2a8af9

diff --git a/manifest b/manifest
index 0dcb6dcb199e01e58edc9695faae6d401aa1e0f0..0e999c04662e4126f22f049a9ff9ba402e8ed2dd 100644 (file)
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Remove\sreferences\sto\sdeleted\sfunction\ssqlite3ExprRegister().\s\sChanges\sto\nthe\sexpr.c\ssource\smodule\sto\spromote\sbetter\stesting.\s(CVS\s6686)
-D 2009-05-28T21:04:38
+C Modify\sthe\shasHotJournal()\sroutine\sto\sreturn\sa\sfalse-positive\sif\sit\sis\nunable\sto\sopen\sthe\sjournal\sfile\sto\scheck\sits\sheader\sdue\sto\sa\srace\ncondition.\s\sProcessing\sdownstream\sof\shasHotJournal()\salready\sknows\show\sto\ndeal\swith\sfalse-positives.\s\sTicket\s#3883.\s(CVS\s6687)
+D 2009-05-29T00:30:30
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in 583e87706abc3026960ed759aff6371faf84c211
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -146,7 +146,7 @@ F src/os_common.h 8c61457df58f1a4bd5f5adc3e90e01b37bf7afbc
 F src/os_os2.c bed77dc26e3a95ce4a204936b9a1ca6fe612fcc5
 F src/os_unix.c e55d977c516ed880a2f83f0610b019efd9f8bc06
 F src/os_win.c 725c38a524d168ce280446ad8761d731bc516405
-F src/pager.c 8bf62fefc7afefc065d37611ebfd1fe0e1c2eb39
+F src/pager.c 6c0fc1c078fcdeefe969a36a186fb147c459c600
 F src/pager.h 73f481a308a873ccd626d97331c081db3b53e2e5
 F src/parse.y 07690df997d50b3fdb5e5121e5a27f1a080db13d
 F src/pcache.c 395f752a13574120bd7513a400ba02a265aaa76d
@@ -731,7 +731,7 @@ F tool/speedtest16.c c8a9c793df96db7e4933f0852abb7a03d48f2e81
 F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
-P 3b46142532934d17aa136c2e56e58e7828df0f54
-R 6a3a4185326252490b36e399fe92cbcc
+P 6ae4ad6ebee4db88c411df97bb1de574708dd53c
+R 3928c5dff5e5480b3ec95781956d3c18
 U drh
-Z 2830ef720e4e0990284e68ba861f067a
+Z a92eea42d5738ee5a30dde1c2bfece9a

diff --git a/manifest.uuid b/manifest.uuid
index 5b6459477dc42ce49b618e3fd826513405812619..89fad15bced1c6cd83bc4cfed36aff0d203bc434 100644 (file)
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-6ae4ad6ebee4db88c411df97bb1de574708dd53c
\ No newline at end of file
+d6b5d8e1ab8e5d3348ace560230702718a2a8af9
\ No newline at end of file

diff --git a/src/pager.c b/src/pager.c
index 9949c11f42ee9a7bd27938146ac68c9ac715bf42..c4c785147d5aea99ddd056ffde45940867d86551 100644 (file)
--- a/src/pager.c
+++ b/src/pager.c
@@ -18,7 +18,7 @@
 ** file simultaneously, or one process from reading the database while
 ** another is writing.
 **
-** @(#) $Id: pager.c,v 1.587 2009/05/13 07:52:06 danielk1977 Exp $
+** @(#) $Id: pager.c,v 1.588 2009/05/29 00:30:30 drh Exp $
 */
 #ifndef SQLITE_OMIT_DISKIO
 #include "sqliteInt.h"
@@ -3384,18 +3384,31 @@ static int hasHotJournal(Pager *pPager, int *pExists){
   rc = sqlite3OsAccess(pVfs, pPager->zJournal, SQLITE_ACCESS_EXISTS, &exists);
   if( rc==SQLITE_OK && exists ){
     int locked;                 /* True if some process holds a RESERVED lock */
+
+    /* Race condition here:  Another process might have been holding the
+    ** the RESERVED lock and have a journal open at the sqlite3OsAccess() 
+    ** call above, but then delete the journal and drop the lock before
+    ** we get to the following sqlite3OsCheckReservedLock() call.  If that
+    ** is the case, this routine might think there is a hot journal when
+    ** in fact there is none.  This results in a false-positive which will
+    ** be dealt with by the playback routine under.  Ticket #3883.
+    */
     rc = sqlite3OsCheckReservedLock(pPager->fd, &locked);
     if( rc==SQLITE_OK && !locked ){
       int nPage;
 
       /* Check the size of the database file. If it consists of 0 pages,
       ** then delete the journal file. See the header comment above for 
-      ** the reasoning here.
+      ** the reasoning here.  Delete the obsolete journal file under
+      ** a RESERVED lock to avoid race conditions.
       */
       rc = sqlite3PagerPagecount(pPager, &nPage);
       if( rc==SQLITE_OK ){
         if( nPage==0 ){
-          rc = sqlite3OsDelete(pVfs, pPager->zJournal, 0);
+          if( sqlite3OsLock(pPager->fd, RESERVED_LOCK)==SQLITE_OK ){
+            sqlite3OsDelete(pVfs, pPager->zJournal, 0);
+            sqlite3OsUnlock(pPager->fd, SHARED_LOCK);
+          }
         }else{
           /* The journal file exists and no other connection has a reserved
           ** or greater lock on the database file. Now check that there is
@@ -3413,6 +3426,18 @@ static int hasHotJournal(Pager *pPager, int *pExists){
             }
             sqlite3OsClose(pPager->jfd);
             *pExists = (first!=0);
+          }else{
+            /* If we cannot open the rollback journal file in order to see if
+            ** its has a zero header, that might be due to an I/O error, or
+            ** it might be due to the race condition described above and in
+            ** ticket #3883.  Either way, assume that the journal is hot.
+            ** This might be a false positive.  But if it is, then the
+            ** automatic journal playback and recovery mechanism will deal
+            ** with it under an EXCLUSIVE lock where we do not need to
+            ** worry so much with race conditions.
+            */
+            *pExists = 1;
+            rc = SQLITE_OK;
           }
         }
       }