From 7d4514a4e16322182a06b2e4e24fc6cd639cff79 Mon Sep 17 00:00:00 2001
From: dan <dan@noemail.net>
Date: Thu, 15 Jul 2010 17:54:14 +0000
Subject: [PATCH] Handle the case where xShmMap returns SQLITE_BUSY.

FossilOrigin-Name: 75f5354876c4300a8e53fe551dc837dd383d1e38
---
 manifest      | 12 ++++++------
 manifest.uuid |  2 +-
 src/wal.c     | 12 ++++++++++--
 3 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/manifest b/manifest
index d0191b4abc..59bd74df4c 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C When\screating\sa\sjournal\sfile\son\sunix,\sattempt\sto\screate\sit\swith\sthe\ssame\spermissions\sas\sthe\sassociated\sdatabase\sfile.
-D 2010-07-15T14:59:38
+C Handle\sthe\scase\swhere\sxShmMap\sreturns\sSQLITE_BUSY.
+D 2010-07-15T17:54:15
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in ec08dc838fd8110fe24c92e5130bcd91cbb1ff2e
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -227,7 +227,7 @@ F src/vdbeblob.c 258a6010ba7a82b72b327fb24c55790655689256
 F src/vdbemem.c 5e579abf6532001dfbee0e640dc34eae897a9807
 F src/vdbetrace.c 864cef96919323482ebd9986f2132435115e9cc2
 F src/vtab.c a0f8a40274e4261696ef57aa806de2776ab72cda
-F src/wal.c 656d50bb0b64f79353110a0b50790edfc0da08e9
+F src/wal.c 66e9034aa9076ce2dbf9ac1ba9fbb9d52ef77c52
 F src/wal.h 906c85760598b18584921fe08008435aa4eeeeb2
 F src/walker.c 3112bb3afe1d85dc52317cb1d752055e9a781f8f
 F src/where.c 903a7828a0a7de03b5d0f1b5eff222d8d5b138f1
@@ -836,7 +836,7 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
-P dea7d33b2d7d25280a31a2b9c1573f4292b81187
-R 68b8490911573c353c565f7397abe3e4
+P a121cd80c5ac94e5977bc3164d2500e0ea132fed
+R b291f8d91c6eb25a36e00bd7f65fa871
 U dan
-Z 3d98b70e949007093904a9e0327dbd7d
+Z 6941f09d52700154471a2c362441f818
diff --git a/manifest.uuid b/manifest.uuid
index dd18395806..773df51172 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-a121cd80c5ac94e5977bc3164d2500e0ea132fed
\ No newline at end of file
+75f5354876c4300a8e53fe551dc837dd383d1e38
\ No newline at end of file
diff --git a/src/wal.c b/src/wal.c
index 769db036da..261bed1963 100644
--- a/src/wal.c
+++ b/src/wal.c
@@ -1866,8 +1866,16 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
       ** WAL_RETRY this routine will be called again and will probably be
       ** right on the second iteration.
       */
-      rc = walLockShared(pWal, WAL_RECOVER_LOCK);
-      if( rc==SQLITE_OK ){
+      if( pWal->apWiData[0]==0 ){
+        /* This branch is taken when the xShmMap() method returns SQLITE_BUSY.
+        ** We assume this is a transient condition, so return WAL_RETRY. The
+        ** xShmMap() implementation used by the default unix and win32 VFS 
+        ** modules may return SQLITE_BUSY due to a race condition in the 
+        ** code that determines whether or not the shared-memory region 
+        ** must be zeroed before the requested page is returned.
+        */
+        rc = WAL_RETRY;
+      }else if( SQLITE_OK==(rc = walLockShared(pWal, WAL_RECOVER_LOCK)) ){
         walUnlockShared(pWal, WAL_RECOVER_LOCK);
         rc = WAL_RETRY;
       }else if( rc==SQLITE_BUSY ){