Modify the sqlite3_log() interface and implementation so that it never

uses dynamic memory allocation - to avoid deadlocking when called while
holding the memory allocator mutex.

FossilOrigin-Name: 28d1bc98d60319b10af427072037a0121bc76259

manifest

@@ -1,5 +1,8 @@
-C Fix\ssome\sextra\sinstances\sof\sthe\sconstants\saddressed\sby\s[83e47ca006].
-D 2010-03-03T16:02:06
+-----BEGIN PGP SIGNED MESSAGE-----
+Hash: SHA1
+
+C Modify\sthe\ssqlite3_log()\sinterface\sand\simplementation\sso\sthat\sit\snever\nuses\sdynamic\smemory\sallocation\s-\sto\savoid\sdeadlocking\swhen\scalled\swhile\nholding\sthe\smemory\sallocator\smutex.
+D 2010-03-03T22:25:18
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in 4f2f967b7e58a35bb74fb7ec8ae90e0f4ca7868b
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -160,13 +163,13 @@ F src/pcache.h c683390d50f856d4cd8e24342ae62027d1bb6050
 F src/pcache1.c 2bb2261190b42a348038f5b1c285c8cef415fcc8
 F src/pragma.c 56d95f76154a5f873c32eae485bb625f3c70be46
 F src/prepare.c c80630169d82945070a50ebf298611fd9f1485f1
-F src/printf.c aa793722d793520fa31c54d81ddab26b0b410562
+F src/printf.c e2b8c9c8d34583dbda4a09fbcb95c522e8467344
 F src/random.c cd4a67b3953b88019f8cd4ccd81394a8ddfaba50
 F src/resolve.c a1648d98e869937b29f4f697461fe4d60f220a7b
 F src/rowset.c 69afa95a97c524ba6faf3805e717b5b7ae85a697
 F src/select.c 4113ef360430ed4e7533690ef46d06c20204adce
 F src/shell.c c40427c7245535a04a9cb4a417b6cc05c022e6a4
-F src/sqlite.h.in 8793d52e7d4e1124dc3cc94ff56376a97b67965f
+F src/sqlite.h.in 08a2d9a278ff0dfd65055a7ec9c599f7ae1a3c18
 F src/sqlite3ext.h 69dfb8116af51b84a029cddb3b35062354270c89
 F src/sqliteInt.h 32e6eb47d2f6fad587e16b0abbbfe3f7d55f2ec0
 F src/sqliteLimit.h 3afab2291762b5d09ae20c18feb8e9fa935a60a6
@@ -792,7 +795,14 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
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manifest.uuid

@@ -1 +1 @@
-0354ab279f0ea9915a14d1ed972b4aa6b5a27fd1
+28d1bc98d60319b10af427072037a0121bc76259

src/printf.c

@@ -939,25 +939,39 @@ char *sqlite3_snprintf(int n, char *zBuf, const char *zFormat, ...){
   return z;
 }
 
+/*
+** This is the routine that actually formats the sqlite3_log() message.
+** We house it in a separate routine from sqlite3_log() to avoid using
+** stack space on small-stack systems when logging is disabled.
+**
+** sqlite3_log() must render into a static buffer.  It cannot dynamically
+** allocate memory because it might be called while the memory allocator
+** mutex is held.
+*/
+static void renderLogMsg(int iErrCode, const char *zFormat, va_list ap){
+  StrAccum acc;                           /* String accumulator */
+#ifdef SQLITE_SMALL_STACK
+  char zMsg[150];                         /* Complete log message */
+#else
+  char zMsg[400];                         /* Complete log message */
+#endif
+
+  sqlite3StrAccumInit(&acc, zMsg, sizeof(zMsg), 0);
+  acc.useMalloc = 0;
+  sqlite3VXPrintf(&acc, 0, zFormat, ap);
+  sqlite3GlobalConfig.xLog(sqlite3GlobalConfig.pLogArg, iErrCode,
+                           sqlite3StrAccumFinish(&acc));
+}
+
 /*
 ** Format and write a message to the log if logging is enabled.
 */
 void sqlite3_log(int iErrCode, const char *zFormat, ...){
-  void (*xLog)(void*, int, const char*);  /* The global logger function */
-  void *pLogArg;                          /* First argument to the logger */
   va_list ap;                             /* Vararg list */
-  char *zMsg;                             /* Complete log message */
-  
-  xLog = sqlite3GlobalConfig.xLog;
-  if( xLog ){
+  if( sqlite3GlobalConfig.xLog ){
     va_start(ap, zFormat);
-    sqlite3BeginBenignMalloc();
-    zMsg = sqlite3_vmprintf(zFormat, ap);
-    sqlite3EndBenignMalloc();
+    renderLogMsg(iErrCode, zFormat, ap);
     va_end(ap);
-    pLogArg = sqlite3GlobalConfig.pLogArg;
-    xLog(pLogArg, iErrCode, zMsg ? zMsg : zFormat);
-    sqlite3_free(zMsg);
   }
 }
 

src/sqlite.h.in

@@ -5705,6 +5705,12 @@ int sqlite3_strnicmp(const char *, const char *, int);
 ** is considered bad form.
 **
 ** The zFormat string must not be NULL.
+**
+** To avoid deadlocks and other threading problems, the sqlite3_log() routine
+** will not use dynamically allocated memory.  The log message is stored in
+** a fixed-length buffer on the stack.  If the log message is longer than
+** a few hundred characters, it will be truncated to the length of the
+** buffer.
 */
 void sqlite3_log(int iErrCode, const char *zFormat, ...);