Merge pull request #299 from qlyoung/perf-improvements

Improve json_object -> string performance

json_object.c

@@ -147,9 +147,12 @@ static int json_escape_str(struct printbuf *pb, const char *str, int len, int fl
 					printbuf_memappend(pb,
 							   str + start_offset,
 							   pos - start_offset);
-				sprintbuf(pb, "\\u00%c%c",
-				json_hex_chars[c >> 4],
-				json_hex_chars[c & 0xf]);
+				static char sbuf[7];
+				snprintf(sbuf, sizeof(sbuf),
+					 "\\u00%c%c",
+					 json_hex_chars[c >> 4],
+					 json_hex_chars[c & 0xf]);
+				printbuf_memappend_fast(pb, sbuf, (int) sizeof(sbuf) - 1);
 				start_offset = ++pos;
 			} else
 				pos++;
@@ -360,29 +363,29 @@ static int json_object_object_to_json_string(struct json_object* jso,
 	int had_children = 0;
 	struct json_object_iter iter;
 
-	sprintbuf(pb, "{" /*}*/);
+	printbuf_strappend(pb, "{" /*}*/);
 	if (flags & JSON_C_TO_STRING_PRETTY)
-		sprintbuf(pb, "\n");
+		printbuf_strappend(pb, "\n");
 	json_object_object_foreachC(jso, iter)
 	{
 		if (had_children)
 		{
-			sprintbuf(pb, ",");
+			printbuf_strappend(pb, ",");
 			if (flags & JSON_C_TO_STRING_PRETTY)
-				sprintbuf(pb, "\n");
+				printbuf_strappend(pb, "\n");
 		}
 		had_children = 1;
 		if (flags & JSON_C_TO_STRING_SPACED)
-			sprintbuf(pb, " ");
+			printbuf_strappend(pb, " ");
 		indent(pb, level+1, flags);
-		sprintbuf(pb, "\"");
+		printbuf_strappend(pb, "\"");
 		json_escape_str(pb, iter.key, strlen(iter.key), flags);
 		if (flags & JSON_C_TO_STRING_SPACED)
-			sprintbuf(pb, "\": ");
+			printbuf_strappend(pb, "\": ");
 		else
-			sprintbuf(pb, "\":");
+			printbuf_strappend(pb, "\":");
 		if(iter.val == NULL)
-			sprintbuf(pb, "null");
+			printbuf_strappend(pb, "null");
 		else
 			if (iter.val->_to_json_string(iter.val, pb, level+1,flags) < 0)
 				return -1;
@@ -390,13 +393,13 @@ static int json_object_object_to_json_string(struct json_object* jso,
 	if (flags & JSON_C_TO_STRING_PRETTY)
 	{
 		if (had_children)
-			sprintbuf(pb, "\n");
+			printbuf_strappend(pb, "\n");
 		indent(pb,level,flags);
 	}
 	if (flags & JSON_C_TO_STRING_SPACED)
-		return sprintbuf(pb, /*{*/ " }");
+		return printbuf_strappend(pb, /*{*/ " }");
 	else
-		return sprintbuf(pb, /*{*/ "}");
+		return printbuf_strappend(pb, /*{*/ "}");
 }
 
 
@@ -537,8 +540,8 @@ static int json_object_boolean_to_json_string(struct json_object* jso,
 					      int flags)
 {
 	if (jso->o.c_boolean)
-		return sprintbuf(pb, "true");
-	return sprintbuf(pb, "false");
+		return printbuf_strappend(pb, "true");
+	return printbuf_strappend(pb, "false");
 }
 
 struct json_object* json_object_new_boolean(json_bool b)
@@ -585,7 +588,10 @@ static int json_object_int_to_json_string(struct json_object* jso,
 					  int level,
 					  int flags)
 {
-	return sprintbuf(pb, "%" PRId64, jso->o.c_int64);
+	/* room for 19 digits, the sign char, and a null term */
+	static char sbuf[21];
+	snprintf(sbuf, sizeof(sbuf), "%"PRId64, jso->o.c_int64);
+	return printbuf_memappend (pb, sbuf, strlen(sbuf));
 }
 
 struct json_object* json_object_new_int(int32_t i)
@@ -853,9 +859,9 @@ static int json_object_string_to_json_string(struct json_object* jso,
 					     int level,
 					     int flags)
 {
-	sprintbuf(pb, "\"");
+	printbuf_strappend(pb, "\"");
 	json_escape_str(pb, get_string_component(jso), jso->o.c_string.len, flags);
-	sprintbuf(pb, "\"");
+	printbuf_strappend(pb, "\"");
 	return 0;
 }
 
@@ -972,25 +978,25 @@ static int json_object_array_to_json_string(struct json_object* jso,
 	int had_children = 0;
 	size_t ii;
 
-	sprintbuf(pb, "[");
+	printbuf_strappend(pb, "[");
 	if (flags & JSON_C_TO_STRING_PRETTY)
-		sprintbuf(pb, "\n");
+		printbuf_strappend(pb, "\n");
 	for(ii=0; ii < json_object_array_length(jso); ii++)
 	{
 		struct json_object *val;
 		if (had_children)
 		{
-			sprintbuf(pb, ",");
+			printbuf_strappend(pb, ",");
 			if (flags & JSON_C_TO_STRING_PRETTY)
-				sprintbuf(pb, "\n");
+				printbuf_strappend(pb, "\n");
 		}
 		had_children = 1;
 		if (flags & JSON_C_TO_STRING_SPACED)
-			sprintbuf(pb, " ");
+			printbuf_strappend(pb, " ");
 		indent(pb, level + 1, flags);
 		val = json_object_array_get_idx(jso, ii);
 		if(val == NULL)
-			sprintbuf(pb, "null");
+			printbuf_strappend(pb, "null");
 		else
 			if (val->_to_json_string(val, pb, level+1, flags) < 0)
 				return -1;
@@ -998,13 +1004,13 @@ static int json_object_array_to_json_string(struct json_object* jso,
 	if (flags & JSON_C_TO_STRING_PRETTY)
 	{
 		if (had_children)
-			sprintbuf(pb, "\n");
+			printbuf_strappend(pb, "\n");
 		indent(pb,level,flags);
 	}
 
 	if (flags & JSON_C_TO_STRING_SPACED)
-		return sprintbuf(pb, " ]");
-	return sprintbuf(pb, "]");
+		return printbuf_strappend(pb, " ]");
+	return printbuf_strappend(pb, "]");
 }
 
 static void json_object_array_entry_free(void *data)

printbuf.h

@@ -29,12 +29,13 @@ struct printbuf {
 extern struct printbuf*
 printbuf_new(void);
 
-/* As an optimization, printbuf_memappend_fast is defined as a macro
+/* As an optimization, printbuf_memappend_fast() is defined as a macro
  * that handles copying data if the buffer is large enough; otherwise
- * it invokes printbuf_memappend_real() which performs the heavy
+ * it invokes printbuf_memappend() which performs the heavy
  * lifting of realloc()ing the buffer and copying data.
- * Your code should not use printbuf_memappend directly--use
- * printbuf_memappend_fast instead.
+ *
+ * Your code should not use printbuf_memappend() directly unless it
+ * checks the return code. Use printbuf_memappend_fast() instead.
  */
 extern int
 printbuf_memappend(struct printbuf *p, const char *buf, int size);
@@ -50,6 +51,28 @@ do {                                                         \
 
 #define printbuf_length(p) ((p)->bpos)
 
+/**
+ * Results in a compile error if the argument is not a string literal.
+ */
+#define _printbuf_check_literal(mystr) ("" mystr)
+
+/**
+ * This is an optimization wrapper around printbuf_memappend() that is useful
+ * for appending string literals. Since the size of string constants is known
+ * at compile time, using this macro can avoid a costly strlen() call. This is
+ * especially helpful when a constant string must be appended many times. If
+ * you got here because of a compilation error caused by passing something
+ * other than a string literal, use printbuf_memappend_fast() in conjunction
+ * with strlen().
+ *
+ * See also:
+ *   printbuf_memappend_fast()
+ *   printbuf_memappend()
+ *   sprintbuf()
+ */
+#define printbuf_strappend(pb, str) \
+   printbuf_memappend ((pb), _printbuf_check_literal(str), sizeof(str) - 1)
+
 /**
  * Set len bytes of the buffer to charvalue, starting at offset offset.
  * Similar to calling memset(x, charvalue, len);
@@ -61,6 +84,20 @@ do {                                                         \
 extern int
 printbuf_memset(struct printbuf *pb, int offset, int charvalue, int len);
 
+/**
+ * Formatted print to printbuf.
+ *
+ * This function is the most expensive of the available functions for appending
+ * string data to a printbuf and should be used only where convenience is more
+ * important than speed. Avoid using this function in high performance code or
+ * tight loops; in these scenarios, consider using snprintf() with a static
+ * buffer in conjunction with one of the printbuf_*append() functions.
+ *
+ * See also:
+ *   printbuf_memappend_fast()
+ *   printbuf_memappend()
+ *   printbuf_strappend()
+ */
 extern int
 sprintbuf(struct printbuf *p, const char *msg, ...);
 

tests/test_printbuf.c

@@ -106,8 +106,15 @@ static void test_printbuf_memappend(int *before_resize)
 	printf("Append to just after resize: %d, [%s]\n", printbuf_length(pb), pb->buf);
 
 	free(data);
+	printbuf_free(pb);
 
+#define SA_TEST_STR "XXXXXXXXXXXXXXXX"
+	pb = printbuf_new();
+	printbuf_strappend(pb, SA_TEST_STR);
+	printf("Buffer size after printbuf_strappend(): %d, [%s]\n", printbuf_length(pb), pb->buf);
 	printbuf_free(pb);
+#undef  SA_TEST_STR
+
 	printf("%s: end test\n", __func__);
 }
 

tests/test_printbuf.expected

@@ -18,6 +18,7 @@ Partial append: 3, [blu]
 With embedded \0 character: 4, [ab]
 Append to just before resize: 31, [XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX]
 Append to just after resize: 32, [XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX]
+Buffer size after printbuf_strappend(): 16, [XXXXXXXXXXXXXXXX]
 test_printbuf_memappend: end test
 ========================================
 test_sprintbuf: starting test