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

replace some magic numbers with appropriate symbolic constants.

FossilOrigin-Name: 13ec8a77a47aa471af587459f4094da0d06674c5960f0d34777bcb3d38bc413b

manifest

@@ -1,5 +1,5 @@
-C Further\scomment\simprovements\sin\swal.c.\s\sNo\scode\schanges.
+C In\swal.c:\simproved\scomments,\snew\sassert()\sand\stestcase()\smacros,\sand\nreplace\ssome\smagic\snumbers\swith\sappropriate\ssymbolic\sconstants.
-D 2017-11-11T13:30:44.595
+D 2017-11-11T20:11:01.646
 F Makefile.in 5bae3f2f3d42f2ad52b141562d74872c97ac0fca6c54953c91bb150a0e6427a8
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc 3a5cb477ec3ce5274663b693164e349db63348667cd45bad78cc13d580b691e2
@@ -543,7 +543,7 @@ F src/vdbesort.c 731a09e5cb9e96b70c394c1b7cf3860fbe84acca7682e178615eb941a3a0ef2
 F src/vdbetrace.c 48e11ebe040c6b41d146abed2602e3d00d621d7ebe4eb29b0a0f1617fd3c2f6c
 F src/vtab.c 0e4885495172e1bdf54b12cce23b395ac74ef5729031f15e1bc1e3e6b360ed1a
 F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
-F src/wal.c 0e19d4fbb52085697509f9407176e732d440f372f49ca08510a65d1aa976bd07
+F src/wal.c 213ddce034c354e640294e77b28097db2a7e10e16c12f6a1158bd7fbcc8e730c
 F src/wal.h 8de5d2d3de0956d6f6cb48c83a4012d5f227b8fe940f3a349a4b7e85ebcb492a
 F src/walker.c d591e8a9ccf60abb010966b354fcea4aa08eba4d83675c2b281a8764c76cc22f
 F src/where.c b7a075f5fb3d912a891dcc3257f538372bb4a1622dd8ca7d752ad95ce8949ba4
@@ -1669,7 +1669,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P d3c25740eec9a2a41c29e6e488fcf6587c1fb821147a442c29439b25a92154a5
+P 346388007de585083dc67ad865b91db7c7d7b78c10a06f8bb7c48767c326c47e
-R cc050d490699d35569ec56a8515bac08
+R cc8d47b78b14e89aa0bda73b44dcaa29
 U drh
-Z 1e870a391397f9beedb8e100937bac44
+Z f012da86d6540243e580ab3866be51e7

manifest.uuid

@@ -1 +1 @@
-346388007de585083dc67ad865b91db7c7d7b78c10a06f8bb7c48767c326c47e
+13ec8a77a47aa471af587459f4094da0d06674c5960f0d34777bcb3d38bc413b

src/wal.c

@@ -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 */
     }
-  };
+  }else{
-  assert( page0 || pWal->writeLock==0 );
+    /* 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 ){
+    if( pWal->exclusiveMode!=WAL_NORMAL_MODE ){
-      pWal->exclusiveMode = 0;
+      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;
 }