Memento: Add Memento_tick()

Sometimes it can be useful to be able to run a program
repeatedly and stop it at a given place, just before a
problem occurs.

Suppose you know that the problem occurs in the 'foo'
function, but only after a number of runs.

Insert a call to Memento_tick() at the top of foo, rebuild
and run in the debugger. When the problem occurs, consult
memento.sequence to see what event number we are on;
suppose it's 1000.

Then you can rerun the debugger with breakpoints on Memento_inited
and Memento_breakpoint. When the program stops at Memento_inited,
call Memento_breakAt(1000) and continue execution. The program
will then stop in Memento_breakpoint within the Memento_tick
call just before the problem occurs, enabling you to step forward
and see what goes wrong.

2 files changed, 15 insertions, 4 deletions

diff --git a/base/memento.c b/base/memento.c
index fd95b6ffa..de3a82134 100644
--- a/base/memento.c
+++ b/base/memento.c
@@ -1529,7 +1529,7 @@ static void Memento_startFailing(void)
     }
 }
 
-static void Memento_event(void)
+static int Memento_event(void)
 {
     memento.sequence++;
     if ((memento.sequence >= memento.paranoidAt) && (memento.paranoidAt != 0)) {
@@ -1550,8 +1550,9 @@ static void Memento_event(void)
 
     if (memento.sequence == memento.breakAt) {
         fprintf(stderr, "Breaking at event %d\n", memento.breakAt);
-        Memento_breakpoint();
+        return 1;
     }
+    return 0;
 }
 
 int Memento_breakAt(int event)
@@ -1573,6 +1574,14 @@ void *Memento_label(void *ptr, const char *label)
     return ptr;
 }
 
+void Memento_tick(void)
+{
+    if (!memento.inited)
+        Memento_init();
+
+    if (Memento_event()) Memento_breakpoint();
+}
+
 int Memento_failThisEvent(void)
 {
     int failThisOne;
@@ -1580,7 +1589,7 @@ int Memento_failThisEvent(void)
     if (!memento.inited)
         Memento_init();
 
-    Memento_event();
+    if (Memento_event()) Memento_breakpoint();
 
     if ((memento.sequence >= memento.failAt) && (memento.failAt != 0))
         Memento_startFailing();
@@ -1783,7 +1792,7 @@ static void do_free(void *blk, int eventType)
     if (!memento.inited)
         Memento_init();
 
-    Memento_event();
+    if (Memento_event()) Memento_breakpoint();
 
     if (blk == NULL)
         return;
diff --git a/base/memento.h b/base/memento.h
index 722c000ea..ec830b41f 100644
--- a/base/memento.h
+++ b/base/memento.h
@@ -214,6 +214,7 @@ void Memento_listNewBlocks(void);
 size_t Memento_setMax(size_t);
 void Memento_stats(void);
 void *Memento_label(void *, const char *);
+void Memento_tick(void);
 
 void *Memento_malloc(size_t s);
 void *Memento_realloc(void *, size_t s);
@@ -265,6 +266,7 @@ void *Memento_reference(void *blk);
 #define Memento_takeRef(A)        (A)
 #define Memento_dropRef(A)        (A)
 #define Memento_reference(A)      (A)
+#define Memento_tick()            do {} while (0)
 
 #endif /* MEMENTO */