From 6045461eee8c9921e1b4155e211e6d944cec41eb Mon Sep 17 00:00:00 2001
From: dan <dan@noemail.net>
Date: Fri, 30 Apr 2010 15:24:43 +0000
Subject: [PATCH] If a reader attempts to upgrade to a writer, but is not
 reading the most recent database snapshot, return SQLITE_BUSY.

FossilOrigin-Name: 837d82a92977cbfa0963411daf8160d286a7ed32
---
 manifest      | 24 +++++++-----------------
 manifest.uuid |  2 +-
 src/wal.c     | 18 ++++++++++++++++++
 3 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/manifest b/manifest
index 63d18faa80..2cf1660e03 100644
--- a/manifest
+++ b/manifest
@@ -1,8 +1,5 @@
------BEGIN PGP SIGNED MESSAGE-----
-Hash: SHA1
-
-C Separate\sthe\sconcepts\sof\sunderlying\sstorage\ssize\sand\smapped\ssize\sin\sthe\nVFS\sshared-memory\simplementation.
-D 2010-04-30T14:39:51
+C If\sa\sreader\sattempts\sto\supgrade\sto\sa\swriter,\sbut\sis\snot\sreading\sthe\smost\srecent\sdatabase\ssnapshot,\sreturn\sSQLITE_BUSY.
+D 2010-04-30T15:24:44
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in d83a0ffef3dcbfb08b410a6c6dd6c009ec9167fb
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -224,7 +221,7 @@ F src/vdbeblob.c 5327132a42a91e8b7acfb60b9d2c3b1c5c863e0e
 F src/vdbemem.c 2a82f455f6ca6f78b59fb312f96054c04ae0ead1
 F src/vdbetrace.c 864cef96919323482ebd9986f2132435115e9cc2
 F src/vtab.c a0f8a40274e4261696ef57aa806de2776ab72cda
-F src/wal.c a4c643582fd9956b46dca187161d466f584b47af
+F src/wal.c 94ebe9e477574baac105975088529f7b141be159
 F src/wal.h c3f347ba8f1cde46d9bcc6fedaf3ed0aa4b53294
 F src/walker.c 3112bb3afe1d85dc52317cb1d752055e9a781f8f
 F src/where.c faadd9c2bf08868e5135192b44e0d753e363a885
@@ -811,14 +808,7 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
-P 1f9e8c5c27ae2c68bc01d8e2bb2c662be7b3f161
-R 2fbe76e11b4a2b6e620f52387007559a
-U drh
-Z 868ea682fbe4fab342b578dc69caee7c
------BEGIN PGP SIGNATURE-----
-Version: GnuPG v1.4.6 (GNU/Linux)
-
-iD8DBQFL2uu6oxKgR168RlERAqI3AJ4jq6FSOAaisShm+qyJakBJL+pVmwCgg1Vd
-tQBOoEYMwVK9lQZSibwuRzM=
-=5suj
------END PGP SIGNATURE-----
+P 4cbe49f13fed288f94ff305bcfd99df907bf7baf
+R a532c500516c30c14fdbbd5b70d5c12a
+U dan
+Z 18b7f313bb88e234cdae10ff0630f7fb
diff --git a/manifest.uuid b/manifest.uuid
index 0313645415..eff7969501 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-4cbe49f13fed288f94ff305bcfd99df907bf7baf
\ No newline at end of file
+837d82a92977cbfa0963411daf8160d286a7ed32
\ No newline at end of file
diff --git a/src/wal.c b/src/wal.c
index 033d1c5232..3bc5bea855 100644
--- a/src/wal.c
+++ b/src/wal.c
@@ -1009,6 +1009,24 @@ int sqlite3WalWriteLock(Wal *pWal, int op){
   if( op ){
     assert( pWal->lockState == SQLITE_SHM_READ );
     rc = walSetLock(pWal, SQLITE_SHM_WRITE);
+
+    /* If this connection is not reading the most recent database snapshot,
+    ** it is not possible to write to the database. In this case release
+    ** the write locks and return SQLITE_BUSY.
+    */
+    if( rc==SQLITE_OK ){
+      rc = walIndexMap(pWal, -1);
+      if( rc==SQLITE_OK 
+       && memcmp(&pWal->hdr, pWal->pWiData, sizeof(WalIndexHdr))
+      ){
+        rc = SQLITE_BUSY;
+      }
+      walIndexUnmap(pWal);
+      if( rc!=SQLITE_OK ){
+        walSetLock(pWal, SQLITE_SHM_READ);
+      }
+    }
+
   }else if( pWal->lockState==SQLITE_SHM_WRITE ){
     rc = walSetLock(pWal, SQLITE_SHM_READ);
   }
-- 
2.47.2