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Extra comments on the sqlite3OsShmMap() call in walBeginUnlocked(). No 

changes to code.

FossilOrigin-Name: 033ee92bf4d5dc57f5cb8fd02d1154ae06f2d3261d214e7191a82c70c8ffebf7
This commit is contained in:
drh 2017-11-08 19:26:27 +00:00
parent 7316960cec
commit 9214c1efe8
3 changed files with 16 additions and 8 deletions
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12
manifest
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@ -1,5 +1,5 @@
C Turns\sout\sthat\sSQLITE_READONLY_CANTLOCK\sis\san\shistorical\sname\sthat\smust\nbe\spreserved.\s\sSo\smake\sa\snew\sSQLITE_READLOCK_CANTINIT\sname\sinstead.
D 2017-11-08T17:51:10.682
C Extra\scomments\son\sthe\ssqlite3OsShmMap()\scall\sin\swalBeginUnlocked().\s\sNo\nchanges\sto\scode.
D 2017-11-08T19:26:27.278
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 b1fef64a242ab30b5fdeeaba49150b420608681673b08833acd17024a179cb1e
F src/wal.c 6903d391b6c224e45910795d66f97151428662c5f459d3b69997209dbcadc6f5
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 6d7f94faa7e6de62f82bc6cac019508a9c1ffd6fa1d14f52fa93e9c06afdd32f
R 1af2a9a9afceb6f159be2ed742a0108b
P 04974a8b5c0e6748216226006ca9125529c8bb2a7a9df4641217eb1413426a14
R eba2a72214a6da7d512bda6426cfe5de
U drh
Z 83682bfec24bdede404f3ec79bae717f
Z 493ea33d970c37f0e10aaccf35cd6d47

2
manifest.uuid
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@ -1 +1 @@
04974a8b5c0e6748216226006ca9125529c8bb2a7a9df4641217eb1413426a14
033ee92bf4d5dc57f5cb8fd02d1154ae06f2d3261d214e7191a82c70c8ffebf7

10
src/wal.c
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@ -2210,6 +2210,14 @@ static int walBeginUnlocked(Wal *pWal, int *pChanged){
/* Try to map the *-shm file again. If it succeeds this time, then
** a non-readonly_shm connection has already connected to the database.
** In this case, start over with opening the transaction.
**
** The *-shm file was opened read-only, so sqlite3OsShmMap() can never
** return SQLITE_OK here, as that would imply that it had established
** a read/write mapping. A return of SQLITE_READONLY means success - that
** a mapping has been established to a shared-memory segment that is actively
** maintained by a writer. SQLITE_READONLY_CANTINIT means that all
** all connections to the -shm file are read-only and hence the content
** of the -shm file might be out-of-date.
**
** The WAL_READ_LOCK(0) lock held by this client prevents a checkpoint
** from taking place. But it does not prevent the wal from being wrapped
@ -2219,8 +2227,8 @@ static int walBeginUnlocked(Wal *pWal, int *pChanged){
** the unlocked transaction, as the other client may overwrite wal
** frames that this client is still using. */
rc = sqlite3OsShmMap(pWal->pDbFd, 0, WALINDEX_PGSZ, 0, &pDummy);
assert( rc!=SQLITE_OK ); /* SQLITE_OK not possible for read-only connection */
if( rc!=SQLITE_READONLY_CANTINIT ){
assert( rc!=SQLITE_OK );
rc = (rc==SQLITE_READONLY ? WAL_RETRY : rc);
goto begin_unlocked_out;
}