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Implement allocate_once for atomic initialization with allocation

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This commit is contained in:
Florian Weimer 2018-05-23 14:16:18 +02:00
parent ed983107bb
commit 5f7b841d3a
6 changed files with 363 additions and 4 deletions
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15
ChangeLog
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@ -1,3 +1,18 @@
2018-05-23 Florian Weimer <fweimer@redhat.com>
Implement allocate_once.
* include/allocate_once.h: New file.
* misc/allocate_once.c: Likewise.
* misc/tst-allocate_once.c: Likewise.
* misc/Makefile (routines): Add allocate_once.
(tests-internal): Add tst-allocate_once.
(generated): Add tst-allocate_once.mtrace,
tst-allocate_once-mem.out.
(tests-special): Add tst-allocate_once-mem.out.
(tst-allocate_once-ENV): Set MALLOC_TRACE.
(tst-allocate_once-mem.out): Call mtrace.
* misc/Versions (GLIBC_PRIVATE): Add __libc_allocate_once_slow.
2018-05-23 H.J. Lu <hongjiu.lu@intel.com>
[BZ #23196]

95
include/allocate_once.h Normal file
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@ -0,0 +1,95 @@
/* Allocate and initialize an object once, in a thread-safe fashion.
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/>. */
#ifndef _ALLOCATE_ONCE_H
#define _ALLOCATE_ONCE_H
#include <atomic.h>
/* Slow path for allocate_once; see below. */
void *__libc_allocate_once_slow (void **__place,
void *(*__allocate) (void *__closure),
void (*__deallocate) (void *__closure,
void *__ptr),
void *__closure);
/* Return an a pointer to an allocated and initialized data structure.
If this function returns a non-NULL value, the caller can assume
that pointed-to data has been initialized according to the ALLOCATE
function.
It is expected that callers define an inline helper function which
adds type safety, like this.
struct foo { ... };
struct foo *global_foo;
static void *allocate_foo (void *closure);
static void *deallocate_foo (void *closure, void *ptr);
static inline struct foo *
get_foo (void)
{
return allocate_once (&global_foo, allocate_foo, free_foo, NULL);
}
(Note that the global_foo variable is initialized to zero.)
Usage of this helper function looks like this:
struct foo *local_foo = get_foo ();
if (local_foo == NULL)
report_allocation_failure ();
allocate_once first performs an acquire MO load on *PLACE. If the
result is not null, it is returned. Otherwise, ALLOCATE (CLOSURE)
is called, yielding a value RESULT. If RESULT equals NULL,
allocate_once returns NULL, and does not modify *PLACE (but another
thread may concurrently perform an allocation which succeeds,
updating *PLACE). If RESULT does not equal NULL, the function uses
a CAS with acquire-release MO to update the NULL value in *PLACE
with the RESULT value. If it turns out that *PLACE was updated
concurrently, allocate_once calls DEALLOCATE (CLOSURE, RESULT) to
undo the effect of ALLOCATE, and returns the new value of *PLACE
(after an acquire MO load). If DEALLOCATE is NULL, free (RESULT)
is called instead.
Compared to __libc_once, allocate_once has the advantage that it
does not need separate space for a control variable, and that it is
safe with regards to cancellation and other forms of exception
handling if the supplied callback functions are safe in that
regard. allocate_once passes a closure parameter to the allocation
function, too. */
static inline void *
allocate_once (void **__place, void *(*__allocate) (void *__closure),
void (*__deallocate) (void *__closure, void *__ptr),
void *__closure)
{
/* Synchronizes with the release MO CAS in
__allocate_once_slow. */
void *__result = atomic_load_acquire (__place);
if (__result != NULL)
return __result;
else
return __libc_allocate_once_slow (__place, __allocate, __deallocate,
__closure);
}
#ifndef _ISOMAC
libc_hidden_proto (__libc_allocate_once_slow)
#endif
#endif /* _ALLOCATE_ONCE_H */

16
misc/Makefile
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@ -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)

1
misc/Versions
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@ -165,5 +165,6 @@ libc {
__tdelete; __tfind; __tsearch; __twalk;
__mmap; __munmap; __mprotect;
__sched_get_priority_min; __sched_get_priority_max;
__libc_allocate_once_slow;
}
}

59
misc/allocate_once.c Normal file
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@ -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)

181
misc/tst-allocate_once.c Normal file
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@ -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>