Add a DTrace probe for string capacity resizes

tenderlove · tenderlove · commit 871841c53aaf · 2019-01-11T12:19:54.000-08:00
diff --git a/probes.d b/probes.d
@@ -151,6 +151,18 @@ provider ruby {
   */
   probe string__create(long length, const char *filename, int lineno);
 
+  /*
+     ruby:::string-capa-resize(from_capa, to_capa, filename, lineno);
+
+     This probe is fired when String capacity is changed
+
+      * `from_capa` the current capacity of the string (long)
+      * `to_capa` the new capacity of the string (long)
+      * `filename` the name of the file where the string is allocated (string)
+      * `lineno` the line number in the file where the string is allocated (int)
+  */
+  probe string__capa__resize(long from_capa, long to_capa, const char *filename, int lineno);
+
   /*
      ruby:::symbol-create(str, filename, lineno);
 
diff --git a/string.c b/string.c
@@ -132,6 +132,18 @@ VALUE rb_cSymbol;
     RESIZE_CAPA_TERM(str,capacity,termlen);\
 } while (0)
 #define RESIZE_CAPA_TERM(str,capacity,termlen) do {\
+    if (UNLIKELY(RUBY_DTRACE_STRING_CAPA_RESIZE_ENABLED())) {\
+	int dtrace_line; \
+	const char *dtrace_file = rb_source_location_cstr(&dtrace_line); \
+	long prev_capa;\
+	if (STR_EMBED_P(str)) {\
+	    prev_capa = RSTRING_EMBED_LEN_MAX + 1 - termlen;\
+	} else {\
+	    prev_capa = RSTRING(str)->as.heap.aux.capa;\
+	}\
+	if (!dtrace_file) dtrace_file = ""; \
+	RUBY_DTRACE_STRING_CAPA_RESIZE(prev_capa, capacity, dtrace_file, dtrace_line);\
+    }\
     if (STR_EMBED_P(str)) {\
 	if (!STR_EMBEDDABLE_P(capacity, termlen)) {\
 	    char *const tmp = ALLOC_N(char, (size_t)(capacity) + (termlen));\
