Merge pull request #2 from json-c/master

merge upstream

Makefile.am

@@ -56,13 +56,43 @@ libjson_c_la_SOURCES = \
 	strerror_override.c \
 	strerror_override_private.h
 
+
+DISTCLEANFILES=
+DISTCLEANFILES+= \
+	config.h \
+	json-c-uninstalled.pc \
+	json-c.pc \
+	json_config.h
+
 distclean-local:
 	-rm -rf $(testsubdir)
-	-rm -rf config.h.in~ Makefile.in aclocal.m4 autom4te.cache/ config.guess config.sub depcomp install-sh ltmain.sh missing
-	-rm -f INSTALL test-driver tests/Makefile.in compile
 
-maintainer-clean-local:
-	-rm -rf configure
+JSON_CLEANFILES=
+JSON_CLEANFILES+= \
+	Makefile.in \
+	aclocal.m4 \
+	autom4te.cache/ \
+	compile \
+	config.guess \
+	config.h.in \
+	config.sub \
+	configure \
+	depcomp \
+	install-sh \
+	ltmain.sh \
+	missing \
+	test-driver \
+	tests/Makefile.in
+JSON_CLEANFILES+= \
+	libtool \
+	stamp-h1 \
+	stamp-h2
+
+# There's no built-in way to remove these after all the other
+# maintainer-clean steps happen, so do it explicitly here.
+really-clean:
+	$(MAKE) maintainer-clean
+	rm -rf ${JSON_CLEANFILES}
 
 uninstall-local:
 	rm -rf "$(DESTDIR)@includedir@/json-c"

README.md

@@ -45,7 +45,7 @@ $ sh autogen.sh
 followed by
 
 ```sh
-$ ./configure
+$ ./configure  # --enable-threading
 $ make
 $ make install
 ```
@@ -56,6 +56,25 @@ To build and run the test programs:
 $ make check
 ```
 
+Building with partial threading support
+----------------------------------------
+
+Although json-c does not support fully multi-threaded access to
+object trees, it has some code to help make use in threaded programs
+a bit safer.  Currently, this is limited to using atomic operations for
+json_object_get() and json_object_put().
+
+Since this may have a performance impact, of at least 3x slower
+according to https://stackoverflow.com/a/11609063, it is disabled by
+default.  You may turn it on by adjusting your configure command with:
+   --enable-threading
+
+Separately, the default hash function used for object field keys,
+lh_char_hash, uses a compare-and-swap operation to ensure the randomly
+seed is only generated once.  Because this is a one-time operation, it
+is always compiled in when the compare-and-swap operation is available.
+
+
 Linking to `libjson-c`
 ----------------------
 

arraylist.c

@@ -22,6 +22,7 @@
 # include <strings.h>
 #endif /* HAVE_STRINGS_H */
 
+#ifndef SIZE_T_MAX
 #if SIZEOF_SIZE_T == SIZEOF_INT
 #define SIZE_T_MAX UINT_MAX
 #elif SIZEOF_SIZE_T == SIZEOF_LONG
@@ -31,6 +32,7 @@
 #else
 #error Unable to determine size of size_t
 #endif
+#endif
 
 #include "arraylist.h"
 

autogen.sh

@@ -1,5 +1,5 @@
 #!/bin/sh
-autoreconf -Iautoconf-archive/m4 -v --install || exit 1
+autoreconf -v --install || exit 1
 
 # If there are any options, assume the user wants to run configure.
 # To run configure w/o any options, use ./autogen.sh --configure

configure.ac

@@ -5,16 +5,32 @@ AC_INIT([json-c], 0.12.99, [json-c@googlegroups.com])
 
 AM_INIT_AUTOMAKE
 
+AC_CONFIG_MACRO_DIRS([autoconf-archive/m4])
+
 AC_PROG_MAKE_SET
 
 AC_CANONICAL_HOST
 
+AC_ARG_ENABLE(threading,
+ AS_HELP_STRING([--enable-threading],
+   [Enable code to support partly multi-threaded use]),
+[if test x$enableval = xyes; then
+  enable_threading=yes
+  AC_DEFINE(ENABLE_THREADING, 1, [Enable partial threading support])
+fi])
+
+if test "x$enable_threading" = "xyes"; then
+  AC_MSG_RESULT([Partial multi-threaded support enabled.])
+else
+  AC_MSG_RESULT([Multi-threaded support disabled. Use --enable-threading to enable.])
+fi
+
 AC_ARG_ENABLE(rdrand,
  AS_HELP_STRING([--enable-rdrand],
    [Enable RDRAND Hardware RNG Hash Seed generation on supported x86/x64 platforms.]),
 [if test x$enableval = xyes; then
   enable_rdrand=yes
-  AC_DEFINE(ENABLE_RDRAND, 1, [Enable RDRANR Hardware RNG Hash Seed])
+  AC_DEFINE(ENABLE_RDRAND, 1, [Enable RDRAND Hardware RNG Hash Seed])
 fi])
 
 if test "x$enable_rdrand" = "xyes"; then
@@ -66,6 +82,30 @@ AC_CHECK_DECLS([isnan], [], [], [[#include <math.h>]])
 AC_CHECK_DECLS([isinf], [], [], [[#include <math.h>]])
 AC_CHECK_DECLS([_isnan], [], [], [[#include <float.h>]])
 AC_CHECK_DECLS([_finite], [], [], [[#include <float.h>]])
+AC_MSG_CHECKING(for GCC atomic builtins)
+AC_LINK_IFELSE(
+[
+ AC_LANG_SOURCE([[
+   int main() {
+      volatile unsigned int val = 1;
+      /* Note: __sync_val_compare_and_swap isn't checked here
+       * because it's protected by __GCC_HAVE_SYNC_COMPARE_AND_SWAP_<n>,
+       * which is automatically defined by gcc.
+       */
+      __sync_add_and_fetch(&val, 1);
+      __sync_sub_and_fetch(&val, 1);
+      return 0;
+   }
+ ]])
+],
+[
+ AC_MSG_RESULT([yes])
+ AC_DEFINE([HAVE_ATOMIC_BUILTINS],[1],[Has atomic builtins])
+],
+[
+ AC_MSG_RESULT([no])
+ AC_MSG_WARN([json-c will be built without atomic refcounts because atomic builtins are missing])
+])
 
 case "${host_os}" in
 	linux*)

json_object.c

@@ -163,25 +163,37 @@ static int json_escape_str(struct printbuf *pb, const char *str, int len, int fl
 
 extern struct json_object* json_object_retain(struct json_object *jso)
 {
-	if (jso)
-		jso->_ref_count++;
+	if (!jso) return jso;
+
+#if defined(HAVE_ATOMIC_BUILTINS) && defined(ENABLE_THREADING)
+	__sync_add_and_fetch(&jso->_ref_count, 1);
+#else
+	++jso->_ref_count;
+#endif        
+
 	return jso;
 }
 
 int json_object_release(struct json_object *jso)
 {
-	if(jso)
-	{
-		jso->_ref_count--;
-		if(!jso->_ref_count)
-		{
-			if (jso->_user_delete)
-				jso->_user_delete(jso, jso->_userdata);
-			jso->_delete(jso);
-			return 1;
-		}
-	}
-	return 0;
+	if(!jso) return 0;
+
+#if defined(HAVE_ATOMIC_BUILTINS) && defined(ENABLE_THREADING)
+	/* Note: this only allow the refcount to remain correct
+	 * when multiple threads are adjusting it.  It is still an error 
+	 * for a thread to decrement the refcount if it doesn't "own" it,
+	 * as that can result in the thread that loses the race to 0
+	 * operating on an already-freed object.
+	 */
+	if (__sync_sub_and_fetch(&jso->_ref_count, 1) > 0) return 0;
+#else
+	if (--jso->_ref_count > 0) return 0;
+#endif
+
+	if (jso->_user_delete)
+		jso->_user_delete(jso, jso->_userdata);
+	jso->_delete(jso);
+	return 1;
 }
 
 
@@ -693,7 +705,7 @@ int json_object_set_int64(struct json_object *jso,int64_t new_value){
 
 /* json_object_double */
 
-#ifdef HAVE___THREAD
+#if defined(HAVE___THREAD)
 // i.e. __thread or __declspec(thread)
 static SPEC___THREAD char *tls_serialization_float_format = NULL;
 #endif
@@ -703,7 +715,7 @@ int json_c_set_serialization_double_format(const char *double_format, int global
 {
 	if (global_or_thread == JSON_C_OPTION_GLOBAL)
 	{
-#ifdef HAVE___THREAD
+#if defined(HAVE___THREAD)
 		if (tls_serialization_float_format)
 		{
 			free(tls_serialization_float_format);
@@ -716,7 +728,7 @@ int json_c_set_serialization_double_format(const char *double_format, int global
 	}
 	else if (global_or_thread == JSON_C_OPTION_THREAD)
 	{
-#ifdef HAVE___THREAD
+#if defined(HAVE___THREAD)
 		if (tls_serialization_float_format)
 		{
 			free(tls_serialization_float_format);
@@ -765,7 +777,7 @@ static int json_object_double_to_json_string_format(struct json_object* jso,
 	{
 		const char *std_format = "%.17g";
 
-#ifdef HAVE___THREAD
+#if defined(HAVE___THREAD)
 		if (tls_serialization_float_format)
 			std_format = tls_serialization_float_format;
 		else

json_util.c

@@ -265,7 +265,9 @@ int json_parse_int64(const char *buf, int64_t *retval)
 		// Skip leading zeros, but keep at least one digit
 		while (buf_sig_digits[0] == '0' && buf_sig_digits[1] != '\0')
 			buf_sig_digits++;
-		if (num64 == 0) // assume all sscanf impl's will parse -0 to 0
+		// Can't check num64==0 because some sscanf impl's parse
+		//  non-zero values to 0.  (e.g. Illumos with UINT64_MAX)
+		if (buf_sig_digits[0] == '0' && buf_sig_digits[1] == '\0')
 			orig_has_neg = 0; // "-0" is the same as just plain "0"
 
 		snprintf(buf_cmp_start, sizeof(buf_cmp), "%" PRId64, num64);