Avoid calling sqlite3_randomness and taking the PRNG mutex when writing a journal header in "journal_mode=memory" mode.

FossilOrigin-Name: c84e4483cb44f827416d8caafa22f076b2f31b2024fe8c5b5bcb0c9955149d11

manifest

@@ -1,5 +1,5 @@
-C Add\sa\sTCL\sscript\sthat\sdoes\svarious\sverification\schecks\son\sthe\ssource\stree\nto\smake\ssure\sthat\sgenerated\scode\shas\sbeen\supdated\scorrectly.
-D 2023-10-09T14:56:15.716
+C Avoid\scalling\ssqlite3_randomness\sand\staking\sthe\sPRNG\smutex\swhen\swriting\sa\sjournal\sheader\sin\s"journal_mode=memory"\smode.
+D 2023-10-09T17:54:34.805
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -701,7 +701,7 @@ F src/os_setup.h 6011ad7af5db4e05155f385eb3a9b4470688de6f65d6166b8956e58a3d87210
 F src/os_unix.c 2e8b12107f75d1bd16412f312b4c5d5103191807a37836d3b81beb26436ad81b
 F src/os_win.c 4a50a154aeebc66a1f8fb79c1ff6dd5fe3d005556533361e0d460d41cb6a45a8
 F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
-F src/pager.c 993445a19b611d473ca007542ab3149840661a4c7e9f2d9e1ec008b7cc2abe78
+F src/pager.c bbd9b93c014679d8148235cc42b73bebda3f598d4f63a63cf7723ddf3087fd58
 F src/pager.h f4d33fec8052603758792045493423b8871a996da2d0973927b7d36cd6070473
 F src/parse.y aeb7760d41cfa86465e3adba506500c021597049fd55f82a30e5b7045862c28c
 F src/pcache.c 040b165f30622a21b7a9a77c6f2e4877a32fb7f22d4c7f0d2a6fa6833a156a75
@@ -2128,8 +2128,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 7e8768bf8b4002b1c287f2bc95262548e2ae81b437936154f2bb1ea1f739a904
-R 12c539e104384e89d6175d6c2ff0dac1
-U drh
-Z ea1222de532c1395014340ac1b27f9c9
+P 1f1a358af77f4386f98010eeae8487e6d39548a6dfe58c2664552490e7661122
+R cb97a01edd9563d34e6c8de016f82192
+U dan
+Z 70f60047d69ba97a07899a1fb54836c4
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-1f1a358af77f4386f98010eeae8487e6d39548a6dfe58c2664552490e7661122
+c84e4483cb44f827416d8caafa22f076b2f31b2024fe8c5b5bcb0c9955149d11

src/pager.c

@@ -1492,9 +1492,32 @@ static int writeJournalHdr(Pager *pPager){
     memset(zHeader, 0, sizeof(aJournalMagic)+4);
   }
 
+
+
   /* The random check-hash initializer */
-  sqlite3_randomness(sizeof(pPager->cksumInit), &pPager->cksumInit);
+  if( pPager->journalMode!=PAGER_JOURNALMODE_MEMORY ){
+    sqlite3_randomness(sizeof(pPager->cksumInit), &pPager->cksumInit);
+  }
+#ifdef SQLITE_DEBUG
+  else{
+    /* The Pager.cksumInit variable is usually randomized above to protect
+    ** against there being existing records in the journal file. This is
+    ** dangerous, as following a crash they may be mistaken for records
+    ** written by the current transaction and rolled back into the database
+    ** file, causing corruption. The following assert statements verify
+    ** that this is not required in "journal_mode=memory" mode, as in that
+    ** case the journal file is always 0 bytes in size at this point. 
+    ** It is advantageous to avoid the sqlite3_randomness() call if possible 
+    ** as it takes the global PRNG mutex.  */
+    i64 sz = 0;
+    sqlite3OsFileSize(pPager->jfd, &sz);
+    assert( sz==0 );
+    assert( pPager->journalOff==journalHdrOffset(pPager) );
+    assert( sqlite3JournalIsInMemory(pPager->jfd) );
+  }
+#endif
   put32bits(&zHeader[sizeof(aJournalMagic)+4], pPager->cksumInit);
+
   /* The initial database size */
   put32bits(&zHeader[sizeof(aJournalMagic)+8], pPager->dbOrigSize);
   /* The assumed sector size for this process */