e70372fcaf
QemuLockable is a polymorphic lock type that takes an object and knows which function to use for locking and unlocking. The implementation could use C11 _Generic, but since the support is not very widespread I am instead using __builtin_choose_expr and __builtin_types_compatible_p, which are already used by include/qemu/atomic.h. QemuLockable can be used to implement lock guards, or to pass around a lock in such a way that a function can release it and re-acquire it. The next patch will do this for CoQueue. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-Id: <20180203153935.8056-3-pbonzini@redhat.com> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Fam Zheng <famz@redhat.com> Signed-off-by: Fam Zheng <famz@redhat.com>
97 lines
2.9 KiB
C
97 lines
2.9 KiB
C
/*
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* Polymorphic locking functions (aka poor man templates)
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*
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* Copyright Red Hat, Inc. 2017, 2018
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*
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* Author: Paolo Bonzini <pbonzini@redhat.com>
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*
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* This work is licensed under the terms of the GNU LGPL, version 2 or later.
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* See the COPYING.LIB file in the top-level directory.
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*
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*/
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#ifndef QEMU_LOCKABLE_H
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#define QEMU_LOCKABLE_H
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#include "qemu/coroutine.h"
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#include "qemu/thread.h"
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typedef void QemuLockUnlockFunc(void *);
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struct QemuLockable {
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void *object;
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QemuLockUnlockFunc *lock;
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QemuLockUnlockFunc *unlock;
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};
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/* This function gives an error if an invalid, non-NULL pointer type is passed
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* to QEMU_MAKE_LOCKABLE. For optimized builds, we can rely on dead-code elimination
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* from the compiler, and give the errors already at link time.
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*/
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#ifdef __OPTIMIZE__
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void unknown_lock_type(void *);
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#else
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static inline void unknown_lock_type(void *unused)
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{
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abort();
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}
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#endif
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static inline __attribute__((__always_inline__)) QemuLockable *
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qemu_make_lockable(void *x, QemuLockable *lockable)
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{
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/* We cannot test this in a macro, otherwise we get compiler
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* warnings like "the address of 'm' will always evaluate as 'true'".
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*/
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return x ? lockable : NULL;
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}
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/* Auxiliary macros to simplify QEMU_MAKE_LOCABLE. */
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#define QEMU_LOCK_FUNC(x) ((QemuLockUnlockFunc *) \
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QEMU_GENERIC(x, \
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(QemuMutex *, qemu_mutex_lock), \
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(CoMutex *, qemu_co_mutex_lock), \
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(QemuSpin *, qemu_spin_lock), \
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unknown_lock_type))
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#define QEMU_UNLOCK_FUNC(x) ((QemuLockUnlockFunc *) \
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QEMU_GENERIC(x, \
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(QemuMutex *, qemu_mutex_unlock), \
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(CoMutex *, qemu_co_mutex_unlock), \
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(QemuSpin *, qemu_spin_unlock), \
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unknown_lock_type))
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/* In C, compound literals have the lifetime of an automatic variable.
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* In C++ it would be different, but then C++ wouldn't need QemuLockable
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* either...
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*/
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#define QEMU_MAKE_LOCKABLE_(x) qemu_make_lockable((x), &(QemuLockable) { \
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.object = (x), \
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.lock = QEMU_LOCK_FUNC(x), \
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.unlock = QEMU_UNLOCK_FUNC(x), \
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})
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/* QEMU_MAKE_LOCKABLE - Make a polymorphic QemuLockable
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*
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* @x: a lock object (currently one of QemuMutex, CoMutex, QemuSpin).
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*
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* Returns a QemuLockable object that can be passed around
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* to a function that can operate with locks of any kind.
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*/
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#define QEMU_MAKE_LOCKABLE(x) \
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QEMU_GENERIC(x, \
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(QemuLockable *, (x)), \
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QEMU_MAKE_LOCKABLE_(x))
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static inline void qemu_lockable_lock(QemuLockable *x)
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{
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x->lock(x->object);
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}
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static inline void qemu_lockable_unlock(QemuLockable *x)
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{
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x->unlock(x->object);
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}
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#endif
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