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authorFlorian Weimer <fweimer@redhat.com>2018-05-23 14:16:18 +0200
committerFlorian Weimer <fweimer@redhat.com>2018-05-23 15:27:01 +0200
commit5f7b841d3aebdccc2baed27cb4b22ddb08cd7c0c (patch)
tree72c894b5b6bbafa8df86036263a5ef584d64bbe3 /misc
parented983107bbc62245b06b99f02e69acf36a0baa3e (diff)
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Implement allocate_once for atomic initialization with allocation
Diffstat (limited to 'misc')
-rw-r--r--misc/Makefile16
-rw-r--r--misc/Versions1
-rw-r--r--misc/allocate_once.c59
-rw-r--r--misc/tst-allocate_once.c181
4 files changed, 253 insertions, 4 deletions
diff --git a/misc/Makefile b/misc/Makefile
index a1d568b..b7be2bc 100644
--- a/misc/Makefile
+++ b/misc/Makefile
@@ -70,9 +70,11 @@ routines := brk sbrk sstk ioctl \
getloadavg getclktck \
fgetxattr flistxattr fremovexattr fsetxattr getxattr \
listxattr lgetxattr llistxattr lremovexattr lsetxattr \
- removexattr setxattr getauxval ifunc-impl-list makedev
+ removexattr setxattr getauxval ifunc-impl-list makedev \
+ allocate_once
-generated += tst-error1.mtrace tst-error1-mem.out
+generated += tst-error1.mtrace tst-error1-mem.out \
+ tst-allocate_once.mtrace tst-allocate_once-mem.out
aux := init-misc
install-lib := libg.a
@@ -84,11 +86,12 @@ tests := tst-dirname tst-tsearch tst-fdset tst-efgcvt tst-mntent tst-hsearch \
tst-preadvwritev tst-preadvwritev64 tst-makedev tst-empty \
tst-preadvwritev2 tst-preadvwritev64v2
-tests-internal := tst-atomic tst-atomic-long
+tests-internal := tst-atomic tst-atomic-long tst-allocate_once
tests-static := tst-empty
ifeq ($(run-built-tests),yes)
-tests-special += $(objpfx)tst-error1-mem.out
+tests-special += $(objpfx)tst-error1-mem.out \
+ $(objpfx)tst-allocate_once-mem.out
endif
CFLAGS-select.c += -fexceptions -fasynchronous-unwind-tables
@@ -137,3 +140,8 @@ tst-error1-ARGS = $(objpfx)tst-error1.out
$(objpfx)tst-error1-mem.out: $(objpfx)tst-error1.out
$(common-objpfx)malloc/mtrace $(objpfx)tst-error1.mtrace > $@; \
$(evaluate-test)
+
+tst-allocate_once-ENV = MALLOC_TRACE=$(objpfx)tst-allocate_once.mtrace
+$(objpfx)tst-allocate_once-mem.out: $(objpfx)tst-allocate_once.out
+ $(common-objpfx)malloc/mtrace $(objpfx)tst-allocate_once.mtrace > $@; \
+ $(evaluate-test)
diff --git a/misc/Versions b/misc/Versions
index bfbda50..900e4ff 100644
--- a/misc/Versions
+++ b/misc/Versions
@@ -165,5 +165,6 @@ libc {
__tdelete; __tfind; __tsearch; __twalk;
__mmap; __munmap; __mprotect;
__sched_get_priority_min; __sched_get_priority_max;
+ __libc_allocate_once_slow;
}
}
diff --git a/misc/allocate_once.c b/misc/allocate_once.c
new file mode 100644
index 0000000..2108014
--- /dev/null
+++ b/misc/allocate_once.c
@@ -0,0 +1,59 @@
+/* Concurrent allocation and initialization of a pointer.
+ Copyright (C) 2018 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <allocate_once.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+void *
+__libc_allocate_once_slow (void **place, void *(*allocate) (void *closure),
+ void (*deallocate) (void *closure, void *ptr),
+ void *closure)
+{
+ void *result = allocate (closure);
+ if (result == NULL)
+ return NULL;
+
+ /* This loop implements a strong CAS on *place, with acquire-release
+ MO semantics, from a weak CAS with relaxed-release MO. */
+ while (true)
+ {
+ /* Synchronizes with the acquire MO load in allocate_once. */
+ void *expected = NULL;
+ if (atomic_compare_exchange_weak_release (place, &expected, result))
+ return result;
+
+ /* The failed CAS has relaxed MO semantics, so perform another
+ acquire MO load. */
+ void *other_result = atomic_load_acquire (place);
+ if (other_result == NULL)
+ /* Spurious failure. Try again. */
+ continue;
+
+ /* We lost the race. Free what we allocated and return the
+ other result. */
+ if (deallocate == NULL)
+ free (result);
+ else
+ deallocate (closure, result);
+ return other_result;
+ }
+
+ return result;
+}
+libc_hidden_def (__libc_allocate_once_slow)
diff --git a/misc/tst-allocate_once.c b/misc/tst-allocate_once.c
new file mode 100644
index 0000000..89277b3
--- /dev/null
+++ b/misc/tst-allocate_once.c
@@ -0,0 +1,181 @@
+/* Test the allocate_once function.
+ Copyright (C) 2018 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <allocate_once.h>
+#include <mcheck.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/support.h>
+
+/* Allocate a new string. */
+static void *
+allocate_string (void *closure)
+{
+ return xstrdup (closure);
+}
+
+/* Allocation and deallocation functions which are not expected to be
+ called. */
+
+static void *
+allocate_not_called (void *closure)
+{
+ FAIL_EXIT1 ("allocation function called unexpectedly (%p)", closure);
+}
+
+static void
+deallocate_not_called (void *closure, void *ptr)
+{
+ FAIL_EXIT1 ("deallocate function called unexpectedly (%p, %p)",
+ closure, ptr);
+}
+
+/* Counter for various function calls. */
+static int function_called;
+
+/* An allocation function which returns NULL and records that it has
+ been called. */
+static void *
+allocate_return_null (void *closure)
+{
+ /* The function should only be called once. */
+ TEST_COMPARE (function_called, 0);
+ ++function_called;
+ return NULL;
+}
+
+
+/* The following is used to check the retry logic, by causing a fake
+ race condition. */
+static void *fake_race_place;
+static char fake_race_region[3]; /* To obtain unique addresses. */
+
+static void *
+fake_race_allocate (void *closure)
+{
+ TEST_VERIFY (closure == &fake_race_region[0]);
+ TEST_COMPARE (function_called, 0);
+ ++function_called;
+ /* Fake allocation by another thread. */
+ fake_race_place = &fake_race_region[1];
+ return &fake_race_region[2];
+}
+
+static void
+fake_race_deallocate (void *closure, void *ptr)
+{
+ /* Check that the pointer returned from fake_race_allocate is
+ deallocated (and not the one stored in fake_race_place). */
+ TEST_VERIFY (ptr == &fake_race_region[2]);
+
+ TEST_VERIFY (fake_race_place == &fake_race_region[1]);
+ TEST_VERIFY (closure == &fake_race_region[0]);
+ TEST_COMPARE (function_called, 1);
+ ++function_called;
+}
+
+/* Similar to fake_race_allocate, but expects to be paired with free
+ as the deallocation function. */
+static void *
+fake_race_allocate_for_free (void *closure)
+{
+ TEST_VERIFY (closure == &fake_race_region[0]);
+ TEST_COMPARE (function_called, 0);
+ ++function_called;
+ /* Fake allocation by another thread. */
+ fake_race_place = &fake_race_region[1];
+ return xstrdup ("to be freed");
+}
+
+static int
+do_test (void)
+{
+ mtrace ();
+
+ /* Simple allocation. */
+ void *place1 = NULL;
+ char *string1 = allocate_once (&place1, allocate_string,
+ deallocate_not_called,
+ (char *) "test string 1");
+ TEST_VERIFY_EXIT (string1 != NULL);
+ TEST_VERIFY (strcmp ("test string 1", string1) == 0);
+ /* Second call returns the first pointer, without calling any
+ callbacks. */
+ TEST_VERIFY (string1
+ == allocate_once (&place1, allocate_not_called,
+ deallocate_not_called,
+ (char *) "test string 1a"));
+
+ /* Different place should result in another call. */
+ void *place2 = NULL;
+ char *string2 = allocate_once (&place2, allocate_string,
+ deallocate_not_called,
+ (char *) "test string 2");
+ TEST_VERIFY_EXIT (string2 != NULL);
+ TEST_VERIFY (strcmp ("test string 2", string2) == 0);
+ TEST_VERIFY (string1 != string2);
+
+ /* Check error reporting (NULL return value from the allocation
+ function). */
+ void *place3 = NULL;
+ char *string3 = allocate_once (&place3, allocate_return_null,
+ deallocate_not_called, NULL);
+ TEST_VERIFY (string3 == NULL);
+ TEST_COMPARE (function_called, 1);
+
+ /* Check that the deallocation function is called if the race is
+ lost. */
+ function_called = 0;
+ TEST_VERIFY (allocate_once (&fake_race_place,
+ fake_race_allocate,
+ fake_race_deallocate,
+ &fake_race_region[0])
+ == &fake_race_region[1]);
+ TEST_COMPARE (function_called, 2);
+ function_called = 3;
+ TEST_VERIFY (allocate_once (&fake_race_place,
+ fake_race_allocate,
+ fake_race_deallocate,
+ &fake_race_region[0])
+ == &fake_race_region[1]);
+ TEST_COMPARE (function_called, 3);
+
+ /* Similar, but this time rely on that free is called. */
+ function_called = 0;
+ fake_race_place = NULL;
+ TEST_VERIFY (allocate_once (&fake_race_place,
+ fake_race_allocate_for_free,
+ NULL,
+ &fake_race_region[0])
+ == &fake_race_region[1]);
+ TEST_COMPARE (function_called, 1);
+ function_called = 3;
+ TEST_VERIFY (allocate_once (&fake_race_place,
+ fake_race_allocate_for_free,
+ NULL,
+ &fake_race_region[0])
+ == &fake_race_region[1]);
+ TEST_COMPARE (function_called, 3);
+
+ free (place2);
+ free (place1);
+
+ return 0;
+}
+
+#include <support/test-driver.c>