89 lines
2.6 KiB
Diff
89 lines
2.6 KiB
Diff
From 63b9fd055248bcd427fd455ce9623431885b235e Mon Sep 17 00:00:00 2001
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From: Nathaniel McCallum <npmccallum@redhat.com>
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Date: Tue, 30 Aug 2016 16:12:22 -0400
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Subject: [PATCH] Add support for the cleanup attribute in GCC/Clang
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The new json_auto_t macro allows easy declaration of json_t types that
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automatically decrement at the end of their scope.
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---
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doc/apiref.rst | 18 ++++++++++++++++++
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src/jansson.h | 13 +++++++++++++
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test/suites/api/test_simple.c | 13 +++++++++++++
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3 files changed, 44 insertions(+)
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diff --git a/doc/apiref.rst b/doc/apiref.rst
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index 0ab2348..2a090e4 100644
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--- a/doc/apiref.rst
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+++ b/doc/apiref.rst
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@@ -253,6 +253,24 @@ other. Moreover, trying to encode the values with any of the encoding
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functions will fail. The encoder detects circular references and
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returns an error status.
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+Scope Dereferencing
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+-------------------
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+
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+It is possible to use the ``json_auto_t`` type to automatically
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+dereference a value at the end of a scope. For example::
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+
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+ void function(void) {
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+ json_auto_t *value = NULL;
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+ value = json_string("foo");
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+ /* json_decref(value) is automatically called. */
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+ }
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+
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+This feature is only available on GCC and Clang. So if your project
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+has a portability requirement for other compilers, you should avoid
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+this feature.
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+
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+Additionally, as always, care should be taken when passing values to
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+functions that steal references.
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True, False and Null
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====================
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diff --git a/src/jansson.h b/src/jansson.h
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index 17a6e7a..b1a040a 100644
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--- a/src/jansson.h
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+++ b/src/jansson.h
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@@ -112,6 +112,19 @@ void json_decref(json_t *json)
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json_delete(json);
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}
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+#if defined(__GNUC__) || defined(__clang__)
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+static JSON_INLINE
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+void json_decrefp(json_t **json)
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+{
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+ if(json) {
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+ json_decref(*json);
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+ *json = NULL;
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+ }
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+}
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+
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+#define json_auto_t json_t __attribute__((cleanup(json_decrefp)))
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+#endif
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+
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/* error reporting */
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diff --git a/test/suites/api/test_simple.c b/test/suites/api/test_simple.c
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index 8b56954..e461561 100644
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--- a/test/suites/api/test_simple.c
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+++ b/test/suites/api/test_simple.c
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@@ -224,4 +224,17 @@ static void run_tests()
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json_incref(value);
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if(value->refcount != (size_t)-1)
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fail("refcounting null works incorrectly");
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+
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+#ifdef json_auto_t
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+ value = json_string("foo");
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+ {
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+ json_auto_t *test = json_incref(value);
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+ /* Use test so GCC doesn't complain it is unused. */
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+ if(!json_is_string(test))
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+ fail("value type check failed");
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+ }
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+ if(value->refcount != 1)
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+ fail("automatic decrement failed");
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+ json_decref(value);
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+#endif
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}
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