SWI portability

os/pl-cstack.c

@@ -89,15 +89,49 @@ get_trace_store(void)
 }
 
 
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+next_btrace_id() produces the  id  for  the   next  backtrace  and  sets
+bt->current to the subsequent id. Although bt is thread-local, it may be
+called from a signal  handler  or   (Windows)  exception.  We cannot use
+locking because the mutex functions are not   async  signal safe. So, we
+use atomic instructions if possible. Otherwise, we ensure consistency of
+the datastructures, but we may overwrite an older stack trace.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+static int
+next_btrace_id(btrace *bt)
+{ int current;
+#ifdef COMPARE_AND_SWAP
+  int next;
+
+  do
+  { current = bt->current;
+    next = current+1;
+    if ( next == SAVE_TRACES )
+      next = 0;
+  } while ( !COMPARE_AND_SWAP(&bt->current, current, next) );
+#else
+  current = bt->current++ % SAVE_TRACES;
+
+  if ( bt->current >= SAVE_TRACES )
+    bt->current %= SAVE_TRACES;
+#endif
+
+  return current;
+}
+
+
 void
 save_backtrace(const char *why)
 { btrace *bt = get_trace_store();
 
   if ( bt )
-  { btrace_stack *s = &bt->dumps[bt->current];
+  { btrace_stack *s;
     unw_cursor_t cursor; unw_context_t uc;
     int depth;
+    int current = next_btrace_id(bt);
 
+    s = &bt->dumps[current];
     unw_getcontext(&uc);
     unw_init_local(&cursor, &uc);
     for(depth=0; unw_step(&cursor) > 0 && depth < MAX_DEPTH; depth++)
@@ -107,9 +141,6 @@ save_backtrace(const char *why)
     }
     s->name = why;
     s->depth = depth;
-
-    if ( ++bt->current == SAVE_TRACES )
-      bt->current = 0;
   }
 
 }
@@ -228,6 +259,33 @@ get_trace_store(void)
 }
 
 
+/* Copy of same function above.  Relies on a different btrace structure.
+   Ideally, this should be shared :-(
+*/
+
+static int
+next_btrace_id(btrace *bt)
+{ int current;
+#ifdef COMPARE_AND_SWAP
+  int next;
+
+  do
+  { current = bt->current;
+    next = current+1;
+    if ( next == SAVE_TRACES )
+      next = 0;
+  } while ( !COMPARE_AND_SWAP(&bt->current, current, next) );
+#else
+  current = bt->current++ % SAVE_TRACES;
+
+  if ( bt->current >= SAVE_TRACES )
+    bt->current %= SAVE_TRACES;
+#endif
+
+  return current;
+}
+
+
 void
 save_backtrace(const char *why)
 { btrace *bt = get_trace_store();
@@ -235,15 +293,14 @@ save_backtrace(const char *why)
   if ( bt )
   { void *array[100];
     size_t frames;
+    int current = next_btrace_id(bt);
 
     frames = backtrace(array, sizeof(array)/sizeof(void *));
-    bt->sizes[bt->current] = frames;
-    if ( bt->symbols[bt->current] )
-      free(bt->symbols[bt->current]);
-    bt->symbols[bt->current] = backtrace_symbols(array, frames);
-    bt->why[bt->current] = why;
-    if ( ++bt->current == SAVE_TRACES )
-      bt->current = 0;
+    bt->sizes[current] = frames;
+    if ( bt->symbols[current] )
+      free(bt->symbols[current]);
+    bt->symbols[current] = backtrace_symbols(array, frames);
+    bt->why[current] = why;
   }
 }
 
@@ -358,6 +415,9 @@ initBackTrace(void)
 */
 #define MAX_MODULE_NAME_LENGTH 64
 
+#define LOCK()   PL_LOCK(L_CSTACK)
+#define UNLOCK() PL_UNLOCK(L_CSTACK)
+
 typedef struct
 { char name[MAX_FUNCTION_NAME_LENGTH];	/* function called */
   DWORD64 offset;			/* offset in function */
@@ -397,6 +457,32 @@ get_trace_store(void)
   return LD->btrace_store;
 }
 
+/* Copy of same function above.  Relies on a different btrace structure.
+   Ideally, this should be shared :-(
+*/
+
+static int
+next_btrace_id(btrace *bt)
+{ int current;
+#ifdef COMPARE_AND_SWAP
+  int next;
+
+  do
+  { current = bt->current;
+    next = current+1;
+    if ( next == SAVE_TRACES )
+      next = 0;
+  } while ( !COMPARE_AND_SWAP(&bt->current, current, next) );
+#else
+  current = bt->current++ % SAVE_TRACES;
+
+  if ( bt->current >= SAVE_TRACES )
+    bt->current %= SAVE_TRACES;
+#endif
+
+  return current;
+}
+
 int backtrace(btrace_stack* trace, PEXCEPTION_POINTERS pExceptionInfo)
 { STACKFRAME64 frame;
   CONTEXT context;
@@ -406,7 +492,6 @@ int backtrace(btrace_stack* trace, PEXCEPTION_POINTERS pExceptionInfo)
   char symbolScratch[sizeof(SYMBOL_INFO) + MAX_SYMBOL_LEN];
   SYMBOL_INFO* symbol = (SYMBOL_INFO*)&symbolScratch;
   IMAGEHLP_MODULE64 moduleInfo;
-  EXCEPTION_POINTERS *pExp = NULL;
   DWORD64 offset;
   DWORD imageType;
   int skip = 0;
@@ -529,11 +614,12 @@ void
 win_save_backtrace(const char *why, PEXCEPTION_POINTERS pExceptionInfo)
 { btrace *bt = get_trace_store();
   if ( bt )
-  { btrace_stack *s = &bt->dumps[bt->current];
+  { int current = next_btrace_id(bt);
+    btrace_stack *s = &bt->dumps[current];
+    LOCK();
     s->depth = backtrace(s, pExceptionInfo);
+    UNLOCK();
     s->name = why;
-    if ( ++bt->current == SAVE_TRACES )
-      bt->current = 0;
   }
 }