Implement allocate_once for atomic initialization with allocation
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ChangeLog
15
ChangeLog
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@ -1,3 +1,18 @@
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2018-05-23 Florian Weimer <fweimer@redhat.com>
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Implement allocate_once.
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* include/allocate_once.h: New file.
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* misc/allocate_once.c: Likewise.
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* misc/tst-allocate_once.c: Likewise.
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* misc/Makefile (routines): Add allocate_once.
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(tests-internal): Add tst-allocate_once.
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(generated): Add tst-allocate_once.mtrace,
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tst-allocate_once-mem.out.
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(tests-special): Add tst-allocate_once-mem.out.
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(tst-allocate_once-ENV): Set MALLOC_TRACE.
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(tst-allocate_once-mem.out): Call mtrace.
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* misc/Versions (GLIBC_PRIVATE): Add __libc_allocate_once_slow.
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2018-05-23 H.J. Lu <hongjiu.lu@intel.com>
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2018-05-23 H.J. Lu <hongjiu.lu@intel.com>
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[BZ #23196]
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[BZ #23196]
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@ -0,0 +1,95 @@
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/* Allocate and initialize an object once, in a thread-safe fashion.
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Copyright (C) 2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef _ALLOCATE_ONCE_H
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#define _ALLOCATE_ONCE_H
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#include <atomic.h>
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/* Slow path for allocate_once; see below. */
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void *__libc_allocate_once_slow (void **__place,
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void *(*__allocate) (void *__closure),
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void (*__deallocate) (void *__closure,
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void *__ptr),
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void *__closure);
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/* Return an a pointer to an allocated and initialized data structure.
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If this function returns a non-NULL value, the caller can assume
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that pointed-to data has been initialized according to the ALLOCATE
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function.
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It is expected that callers define an inline helper function which
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adds type safety, like this.
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struct foo { ... };
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struct foo *global_foo;
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static void *allocate_foo (void *closure);
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static void *deallocate_foo (void *closure, void *ptr);
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static inline struct foo *
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get_foo (void)
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{
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return allocate_once (&global_foo, allocate_foo, free_foo, NULL);
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}
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(Note that the global_foo variable is initialized to zero.)
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Usage of this helper function looks like this:
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struct foo *local_foo = get_foo ();
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if (local_foo == NULL)
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report_allocation_failure ();
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allocate_once first performs an acquire MO load on *PLACE. If the
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result is not null, it is returned. Otherwise, ALLOCATE (CLOSURE)
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is called, yielding a value RESULT. If RESULT equals NULL,
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allocate_once returns NULL, and does not modify *PLACE (but another
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thread may concurrently perform an allocation which succeeds,
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updating *PLACE). If RESULT does not equal NULL, the function uses
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a CAS with acquire-release MO to update the NULL value in *PLACE
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with the RESULT value. If it turns out that *PLACE was updated
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concurrently, allocate_once calls DEALLOCATE (CLOSURE, RESULT) to
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undo the effect of ALLOCATE, and returns the new value of *PLACE
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(after an acquire MO load). If DEALLOCATE is NULL, free (RESULT)
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is called instead.
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Compared to __libc_once, allocate_once has the advantage that it
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does not need separate space for a control variable, and that it is
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safe with regards to cancellation and other forms of exception
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handling if the supplied callback functions are safe in that
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regard. allocate_once passes a closure parameter to the allocation
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function, too. */
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static inline void *
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allocate_once (void **__place, void *(*__allocate) (void *__closure),
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void (*__deallocate) (void *__closure, void *__ptr),
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void *__closure)
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{
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/* Synchronizes with the release MO CAS in
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__allocate_once_slow. */
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void *__result = atomic_load_acquire (__place);
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if (__result != NULL)
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return __result;
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else
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return __libc_allocate_once_slow (__place, __allocate, __deallocate,
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__closure);
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}
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#ifndef _ISOMAC
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libc_hidden_proto (__libc_allocate_once_slow)
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#endif
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#endif /* _ALLOCATE_ONCE_H */
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@ -70,9 +70,11 @@ routines := brk sbrk sstk ioctl \
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getloadavg getclktck \
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getloadavg getclktck \
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fgetxattr flistxattr fremovexattr fsetxattr getxattr \
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fgetxattr flistxattr fremovexattr fsetxattr getxattr \
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listxattr lgetxattr llistxattr lremovexattr lsetxattr \
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listxattr lgetxattr llistxattr lremovexattr lsetxattr \
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removexattr setxattr getauxval ifunc-impl-list makedev
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removexattr setxattr getauxval ifunc-impl-list makedev \
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allocate_once
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generated += tst-error1.mtrace tst-error1-mem.out
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generated += tst-error1.mtrace tst-error1-mem.out \
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tst-allocate_once.mtrace tst-allocate_once-mem.out
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aux := init-misc
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aux := init-misc
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install-lib := libg.a
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install-lib := libg.a
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@ -84,11 +86,12 @@ tests := tst-dirname tst-tsearch tst-fdset tst-efgcvt tst-mntent tst-hsearch \
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tst-preadvwritev tst-preadvwritev64 tst-makedev tst-empty \
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tst-preadvwritev tst-preadvwritev64 tst-makedev tst-empty \
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tst-preadvwritev2 tst-preadvwritev64v2
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tst-preadvwritev2 tst-preadvwritev64v2
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tests-internal := tst-atomic tst-atomic-long
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tests-internal := tst-atomic tst-atomic-long tst-allocate_once
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tests-static := tst-empty
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tests-static := tst-empty
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ifeq ($(run-built-tests),yes)
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ifeq ($(run-built-tests),yes)
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tests-special += $(objpfx)tst-error1-mem.out
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tests-special += $(objpfx)tst-error1-mem.out \
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$(objpfx)tst-allocate_once-mem.out
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endif
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endif
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CFLAGS-select.c += -fexceptions -fasynchronous-unwind-tables
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CFLAGS-select.c += -fexceptions -fasynchronous-unwind-tables
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@ -137,3 +140,8 @@ tst-error1-ARGS = $(objpfx)tst-error1.out
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$(objpfx)tst-error1-mem.out: $(objpfx)tst-error1.out
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$(objpfx)tst-error1-mem.out: $(objpfx)tst-error1.out
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$(common-objpfx)malloc/mtrace $(objpfx)tst-error1.mtrace > $@; \
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$(common-objpfx)malloc/mtrace $(objpfx)tst-error1.mtrace > $@; \
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$(evaluate-test)
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$(evaluate-test)
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tst-allocate_once-ENV = MALLOC_TRACE=$(objpfx)tst-allocate_once.mtrace
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$(objpfx)tst-allocate_once-mem.out: $(objpfx)tst-allocate_once.out
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$(common-objpfx)malloc/mtrace $(objpfx)tst-allocate_once.mtrace > $@; \
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$(evaluate-test)
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@ -165,5 +165,6 @@ libc {
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__tdelete; __tfind; __tsearch; __twalk;
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__tdelete; __tfind; __tsearch; __twalk;
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__mmap; __munmap; __mprotect;
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__mmap; __munmap; __mprotect;
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__sched_get_priority_min; __sched_get_priority_max;
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__sched_get_priority_min; __sched_get_priority_max;
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__libc_allocate_once_slow;
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}
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}
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}
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}
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@ -0,0 +1,59 @@
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/* Concurrent allocation and initialization of a pointer.
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Copyright (C) 2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <allocate_once.h>
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#include <stdlib.h>
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#include <stdbool.h>
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void *
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__libc_allocate_once_slow (void **place, void *(*allocate) (void *closure),
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void (*deallocate) (void *closure, void *ptr),
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void *closure)
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{
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void *result = allocate (closure);
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if (result == NULL)
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return NULL;
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/* This loop implements a strong CAS on *place, with acquire-release
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MO semantics, from a weak CAS with relaxed-release MO. */
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while (true)
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{
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/* Synchronizes with the acquire MO load in allocate_once. */
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void *expected = NULL;
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if (atomic_compare_exchange_weak_release (place, &expected, result))
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return result;
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/* The failed CAS has relaxed MO semantics, so perform another
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acquire MO load. */
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void *other_result = atomic_load_acquire (place);
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if (other_result == NULL)
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/* Spurious failure. Try again. */
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continue;
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/* We lost the race. Free what we allocated and return the
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other result. */
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if (deallocate == NULL)
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free (result);
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else
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deallocate (closure, result);
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return other_result;
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}
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return result;
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}
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libc_hidden_def (__libc_allocate_once_slow)
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@ -0,0 +1,181 @@
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/* Test the allocate_once function.
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Copyright (C) 2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <allocate_once.h>
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#include <mcheck.h>
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#include <string.h>
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#include <support/check.h>
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#include <support/support.h>
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/* Allocate a new string. */
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static void *
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allocate_string (void *closure)
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{
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return xstrdup (closure);
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}
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/* Allocation and deallocation functions which are not expected to be
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called. */
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static void *
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allocate_not_called (void *closure)
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{
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FAIL_EXIT1 ("allocation function called unexpectedly (%p)", closure);
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}
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static void
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deallocate_not_called (void *closure, void *ptr)
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{
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FAIL_EXIT1 ("deallocate function called unexpectedly (%p, %p)",
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closure, ptr);
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}
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/* Counter for various function calls. */
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static int function_called;
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/* An allocation function which returns NULL and records that it has
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been called. */
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static void *
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allocate_return_null (void *closure)
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{
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/* The function should only be called once. */
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TEST_COMPARE (function_called, 0);
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++function_called;
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return NULL;
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}
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/* The following is used to check the retry logic, by causing a fake
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race condition. */
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static void *fake_race_place;
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static char fake_race_region[3]; /* To obtain unique addresses. */
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static void *
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fake_race_allocate (void *closure)
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{
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TEST_VERIFY (closure == &fake_race_region[0]);
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TEST_COMPARE (function_called, 0);
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++function_called;
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/* Fake allocation by another thread. */
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fake_race_place = &fake_race_region[1];
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return &fake_race_region[2];
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}
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static void
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fake_race_deallocate (void *closure, void *ptr)
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{
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/* Check that the pointer returned from fake_race_allocate is
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deallocated (and not the one stored in fake_race_place). */
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TEST_VERIFY (ptr == &fake_race_region[2]);
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TEST_VERIFY (fake_race_place == &fake_race_region[1]);
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TEST_VERIFY (closure == &fake_race_region[0]);
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TEST_COMPARE (function_called, 1);
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++function_called;
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}
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/* Similar to fake_race_allocate, but expects to be paired with free
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as the deallocation function. */
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static void *
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fake_race_allocate_for_free (void *closure)
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{
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TEST_VERIFY (closure == &fake_race_region[0]);
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TEST_COMPARE (function_called, 0);
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++function_called;
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/* Fake allocation by another thread. */
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fake_race_place = &fake_race_region[1];
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return xstrdup ("to be freed");
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}
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static int
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do_test (void)
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{
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mtrace ();
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/* Simple allocation. */
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void *place1 = NULL;
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char *string1 = allocate_once (&place1, allocate_string,
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deallocate_not_called,
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(char *) "test string 1");
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TEST_VERIFY_EXIT (string1 != NULL);
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TEST_VERIFY (strcmp ("test string 1", string1) == 0);
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/* Second call returns the first pointer, without calling any
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callbacks. */
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TEST_VERIFY (string1
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== allocate_once (&place1, allocate_not_called,
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deallocate_not_called,
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(char *) "test string 1a"));
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/* Different place should result in another call. */
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void *place2 = NULL;
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char *string2 = allocate_once (&place2, allocate_string,
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deallocate_not_called,
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(char *) "test string 2");
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TEST_VERIFY_EXIT (string2 != NULL);
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TEST_VERIFY (strcmp ("test string 2", string2) == 0);
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TEST_VERIFY (string1 != string2);
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/* Check error reporting (NULL return value from the allocation
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function). */
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void *place3 = NULL;
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char *string3 = allocate_once (&place3, allocate_return_null,
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deallocate_not_called, NULL);
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TEST_VERIFY (string3 == NULL);
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TEST_COMPARE (function_called, 1);
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/* 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>
|
Loading…
Reference in New Issue