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gatomic: Add APIs to perform atomic int / pointer exchanges

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Atomic APIs provide a way to exchange values only if we compare a value
that is equal to the old value, but not to just exchange the value
returning the old one.

However, compilers provide such built-in functions, so we can use them
to expose such functionality to GLib.

The only drawback is that when using an old version of gcc not providing
atomic APIs to swap values, we need to re-implement it with an
implementation that may not be fully atomic, but that is safe enough.

However this codepath should really not be used currently as gcc
introduced __atomic_exchange_n() at version 4.7.4, so 8 years ago.
This commit is contained in:
Marco Trevisan (Treviño)
2022-06-06 21:30:41 +02:00
parent 2b437402e8
commit fa4e34667c
6 changed files with 235 additions and 0 deletions
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30
glib/tests/atomic.c
View File

@@ -56,6 +56,9 @@ test_types (void)
u2 = g_atomic_int_xor (&u, 4);
g_assert_cmpint (u2, ==, 12);
g_assert_cmpint (u, ==, 8);
u2 = g_atomic_int_exchange (&u, 55);
g_assert_cmpint (u2, ==, 8);
g_assert_cmpint (u, ==, 55);
g_atomic_int_set (&s, 5);
s2 = g_atomic_int_get (&s);
@@ -79,6 +82,9 @@ test_types (void)
s2 = (gint) g_atomic_int_xor (&s, 4);
g_assert_cmpint (s2, ==, 12);
g_assert_cmpint (s, ==, 8);
s2 = g_atomic_int_exchange (&s, 55);
g_assert_cmpint (s2, ==, 8);
g_assert_cmpint (s, ==, 55);
g_atomic_pointer_set (&vp, 0);
vp2 = g_atomic_pointer_get (&vp);
@@ -89,10 +95,14 @@ test_types (void)
res = g_atomic_pointer_compare_and_exchange (&vp, NULL, NULL);
g_assert_true (res);
g_assert_true (vp == 0);
g_assert_null (g_atomic_pointer_exchange (&vp, &s));
g_assert_true (vp == &s);
g_atomic_pointer_set (&vp_str, NULL);
res = g_atomic_pointer_compare_and_exchange (&vp_str, NULL, str);
g_assert_true (res);
g_assert_cmpstr (g_atomic_pointer_exchange (&vp_str, NULL), ==, str);
g_assert_null (vp_str);
/* Note that atomic variables should almost certainly not be marked as
* `volatile` — see http://isvolatileusefulwiththreads.in/c/. This test exists
@@ -130,6 +140,10 @@ test_types (void)
gs2 = g_atomic_pointer_xor (&gs, 4);
g_assert_cmpuint (gs2, ==, 12);
g_assert_cmpuint (gs, ==, 8);
vp2 = g_atomic_pointer_exchange ((gpointer*) &gs, NULL);
gs2 = (gsize) vp2;
g_assert_cmpuint (gs2, ==, 8);
g_assert_null ((gpointer) gs);
g_assert_cmpint (g_atomic_int_get (csp), ==, s);
g_assert_true (g_atomic_pointer_get ((const gint **) cspp) == csp);
@@ -138,6 +152,7 @@ test_types (void)
#undef g_atomic_int_set
#undef g_atomic_int_get
#undef g_atomic_int_compare_and_exchange
#undef g_atomic_int_exchange
#undef g_atomic_int_add
#undef g_atomic_int_inc
#undef g_atomic_int_and
@@ -147,6 +162,7 @@ test_types (void)
#undef g_atomic_pointer_set
#undef g_atomic_pointer_get
#undef g_atomic_pointer_compare_and_exchange
#undef g_atomic_pointer_exchange
#undef g_atomic_pointer_add
#undef g_atomic_pointer_and
#undef g_atomic_pointer_or
@@ -173,6 +189,9 @@ test_types (void)
g_assert_cmpint (u, ==, 12);
u2 = g_atomic_int_xor (&u, 4);
g_assert_cmpint (u2, ==, 12);
u2 = g_atomic_int_exchange (&u, 55);
g_assert_cmpint (u2, ==, 8);
g_assert_cmpint (u, ==, 55);
g_atomic_int_set (&s, 5);
s2 = g_atomic_int_get (&s);
@@ -201,6 +220,9 @@ G_GNUC_BEGIN_IGNORE_DEPRECATIONS
G_GNUC_END_IGNORE_DEPRECATIONS
g_assert_cmpint (s2, ==, 8);
g_assert_cmpint (s, ==, 9);
s2 = g_atomic_int_exchange (&s, 55);
g_assert_cmpint (s2, ==, 9);
g_assert_cmpint (s, ==, 55);
g_atomic_pointer_set (&vp, 0);
vp2 = g_atomic_pointer_get (&vp);
@@ -211,6 +233,8 @@ G_GNUC_END_IGNORE_DEPRECATIONS
res = g_atomic_pointer_compare_and_exchange (&vp, NULL, NULL);
g_assert_true (res);
g_assert_true (vp == 0);
g_assert_null (g_atomic_pointer_exchange (&vp, &s));
g_assert_true (vp == &s);
g_atomic_pointer_set (&vp_str, NULL);
res = g_atomic_pointer_compare_and_exchange (&vp_str, NULL, (char *) str);
@@ -222,6 +246,8 @@ G_GNUC_END_IGNORE_DEPRECATIONS
g_atomic_pointer_set (&vp_str_vol, NULL);
res = g_atomic_pointer_compare_and_exchange (&vp_str_vol, NULL, (char *) str);
g_assert_true (res);
g_assert_cmpstr (g_atomic_pointer_exchange (&vp_str, NULL), ==, str);
g_assert_null (vp_str);
g_atomic_pointer_set (&ip, 0);
ip2 = g_atomic_pointer_get (&ip);
@@ -249,6 +275,10 @@ G_GNUC_END_IGNORE_DEPRECATIONS
gs2 = g_atomic_pointer_xor (&gs, 4);
g_assert_cmpuint (gs2, ==, 12);
g_assert_cmpuint (gs, ==, 8);
vp2 = g_atomic_pointer_exchange ((gpointer*) &gs, NULL);
gs2 = (gsize) vp2;
g_assert_cmpuint (gs2, ==, 8);
g_assert_null ((gpointer) gs);
g_assert_cmpint (g_atomic_int_get (csp), ==, s);
g_assert_true (g_atomic_pointer_get (cspp) == csp);

35
glib/tests/cxx.cpp
View File

@@ -87,6 +87,39 @@ test_atomic_int_compare_and_exchange (void)
#endif
}
static void
test_atomic_pointer_exchange (void)
{
#if __cplusplus >= 201103L
const gchar *str1 = "str1";
const gchar *str2 = "str2";
const gchar *atomic_string = str1;
g_test_message ("Test that g_atomic_pointer_exchange() with a "
"non-void* pointer doesn’t have any compiler warnings in C++ mode");
g_assert_true (g_atomic_pointer_exchange (&atomic_string, str2) == str1);
g_assert_true (atomic_string == str2);
#else
g_test_skip ("This test requires a C++11 compiler");
#endif
}
static void
test_atomic_int_exchange (void)
{
#if __cplusplus >= 201103L
gint atomic_int = 5;
g_test_message ("Test that g_atomic_int_compare_and_exchange() doesn’t have "
"any compiler warnings in C++ mode");
g_assert_cmpint (g_atomic_int_exchange (&atomic_int, 50), ==, 5);
#else
g_test_skip ("This test requires a C++11 compiler");
#endif
}
int
main (int argc, char *argv[])
{
@@ -99,6 +132,8 @@ main (int argc, char *argv[])
g_test_add_func ("/C++/typeof", test_typeof);
g_test_add_func ("/C++/atomic-pointer-compare-and-exchange", test_atomic_pointer_compare_and_exchange);
g_test_add_func ("/C++/atomic-int-compare-and-exchange", test_atomic_int_compare_and_exchange);
g_test_add_func ("/C++/atomic-pointer-exchange", test_atomic_pointer_exchange);
g_test_add_func ("/C++/atomic-int-exchange", test_atomic_int_exchange);
return g_test_run ();
}