Add the test_oom_breakpoint() routine on debug builds, to serve as a

convenient breakpoint to intercept OOM conditions.

FossilOrigin-Name: e45df7dcd6b5766d7593ee87e59dd422a217cce0a1a8d369c03144bb21859428

src/malloc.c

@@ -221,6 +221,24 @@ static void sqlite3MallocAlarm(int nByte){
   sqlite3_mutex_enter(mem0.mutex);
 }
 
+#ifdef SQLITE_DEBUG
+/*
+** This routine is called whenever an out-of-memory condition is seen,
+** It's only purpose to to serve as a breakpoint for gdb or similar
+** code debuggers when working on out-of-memory conditions, for example
+** caused by PRAGMA hard_heap_limit=N.
+*/
+static SQLITE_NOINLINE void test_oom_breakpoint(void){
+  static u64 nOomFault = 0;
+  nOomFault++;
+  /* The assert() is never reached in a human lifetime.  It  is here mostly
+  ** to prevent code optimizers from optimizing out this function. */
+  assert( (nOomFault>>32) < 0xffffffff );
+}
+#else
+# define test_oom_breakpoint(X)   /* No-op for production builds */
+#endif
+
 /*
 ** Do a memory allocation with statistics and alarms.  Assume the
 ** lock is already held.
@@ -247,6 +265,7 @@ static void mallocWithAlarm(int n, void **pp){
       if( mem0.hardLimit ){
         nUsed = sqlite3StatusValue(SQLITE_STATUS_MEMORY_USED);
         if( nUsed >= mem0.hardLimit - nFull ){
+          test_oom_breakpoint();
           *pp = 0;
           return;
         }
@@ -535,6 +554,7 @@ void *sqlite3Realloc(void *pOld, u64 nBytes){
       sqlite3MallocAlarm(nDiff);
       if( mem0.hardLimit>0 && nUsed >= mem0.hardLimit - nDiff ){
         sqlite3_mutex_leave(mem0.mutex);
+        test_oom_breakpoint();
         return 0;
       }
     }