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 <pbonz...@redhat.com>
---
include/qemu/compiler.h | 40 ++++++++++++++++++++
include/qemu/coroutine.h | 4 +-
include/qemu/lockable.h | 96 ++++++++++++++++++++++++++++++++++++++++++++++++
include/qemu/thread.h | 5 +--
include/qemu/typedefs.h | 4 ++
tests/test-coroutine.c | 25 +++++++++++++
6 files changed, 169 insertions(+), 5 deletions(-)
create mode 100644 include/qemu/lockable.h
diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index 340e5fdc09..5179bedb1e 100644
--- a/include/qemu/compiler.h
+++ b/include/qemu/compiler.h
@@ -111,4 +111,44 @@
#define GCC_FMT_ATTR(n, m)
#endif
+/* Implement C11 _Generic via GCC builtins. Example:
+ *
+ * QEMU_GENERIC(x, (float, sinf), (long double, sinl), sin) (x)
+ *
+ * The first argument is the discriminator. The last is the default value.
+ * The middle ones are tuples in "(type, expansion)" format.
+ */
+
+/* First, find out the number of generic cases. */
+#define QEMU_GENERIC(x, ...) \
+ QEMU_GENERIC_(typeof(x), __VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
+
+/* There will be extra arguments, but they are not used. */
+#define QEMU_GENERIC_(x, a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, count, ...) \
+ QEMU_GENERIC##count(x, a0, a1, a2, a3, a4, a5, a6, a7, a8, a9)
+
+/* Two more helper macros, this time to extract items from a parenthesized
+ * list.
+ */
+#define QEMU_FIRST_(a, b) a
+#define QEMU_SECOND_(a, b) b
+
+/* ... and a final one for the common part of the "recursion". */
+#define QEMU_GENERIC_IF(x, type_then, else_)
\
+ __builtin_choose_expr(__builtin_types_compatible_p(x,
\
+ QEMU_FIRST_ type_then),
\
+ QEMU_SECOND_ type_then, else_)
+
+/* CPP poor man's "recursion". */
+#define QEMU_GENERIC1(x, a0, ...) (a0)
+#define QEMU_GENERIC2(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC1(x,
__VA_ARGS__))
+#define QEMU_GENERIC3(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC2(x,
__VA_ARGS__))
+#define QEMU_GENERIC4(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC3(x,
__VA_ARGS__))
+#define QEMU_GENERIC5(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC4(x,
__VA_ARGS__))
+#define QEMU_GENERIC6(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC5(x,
__VA_ARGS__))
+#define QEMU_GENERIC7(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC6(x,
__VA_ARGS__))
+#define QEMU_GENERIC8(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC7(x,
__VA_ARGS__))
+#define QEMU_GENERIC9(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC8(x,
__VA_ARGS__))
+#define QEMU_GENERIC10(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC9(x,
__VA_ARGS__))
+
#endif /* COMPILER_H */
diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h
index ce2eb73670..8a5129741c 100644
--- a/include/qemu/coroutine.h
+++ b/include/qemu/coroutine.h
@@ -121,7 +121,7 @@ bool qemu_coroutine_entered(Coroutine *co);
* Provides a mutex that can be used to synchronise coroutines
*/
struct CoWaitRecord;
-typedef struct CoMutex {
+struct CoMutex {
/* Count of pending lockers; 0 for a free mutex, 1 for an
* uncontended mutex.
*/
@@ -142,7 +142,7 @@ typedef struct CoMutex {
unsigned handoff, sequence;
Coroutine *holder;
-} CoMutex;
+};
/**
* Initialises a CoMutex. This must be called before any other operation is
used
diff --git a/include/qemu/lockable.h b/include/qemu/lockable.h
new file mode 100644
index 0000000000..826ac3f675
--- /dev/null
+++ b/include/qemu/lockable.h
@@ -0,0 +1,96 @@
+/*
+ * Polymorphic locking functions (aka poor man templates)
+ *
+ * Copyright Red Hat, Inc. 2017, 2018
+ *
+ * Author: Paolo Bonzini <pbonz...@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ *
+ */
+
+#ifndef QEMU_LOCKABLE_H
+#define QEMU_LOCKABLE_H
+
+#include "qemu/coroutine.h"
+#include "qemu/thread.h"
+
+typedef void QemuLockUnlockFunc(void *);
+
+struct QemuLockable {
+ void *object;
+ QemuLockUnlockFunc *lock;
+ QemuLockUnlockFunc *unlock;
+};
+
+/* This function gives an error if an invalid, non-NULL pointer type is passed
+ * to QEMU_MAKE_LOCKABLE. For optimized builds, we can rely on dead-code
elimination
+ * from the compiler, and give the errors already at link time.
+ */
+#ifdef __OPTIMIZE__
+void unknown_lock_type(void *);
+#else
+static inline void unknown_lock_type(void *unused)
+{
+ abort();
+}
+#endif
+
+static inline __attribute__((__always_inline__)) QemuLockable *
+qemu_make_lockable(void *x, QemuLockable *lockable)
+{
+ /* We cannot test this in a macro, otherwise we get compiler
+ * warnings like "the address of 'm' will always evaluate as 'true'".
+ */
+ return x ? lockable : NULL;
+}
+
+/* Auxiliary macros to simplify QEMU_MAKE_LOCABLE. */
+#define QEMU_LOCK_FUNC(x) ((QemuLockUnlockFunc *) \
+ QEMU_GENERIC(x, \
+ (QemuMutex *, qemu_mutex_lock), \
+ (CoMutex *, qemu_co_mutex_lock), \
+ (QemuSpin *, qemu_spin_lock), \
+ unknown_lock_type))
+
+#define QEMU_UNLOCK_FUNC(x) ((QemuLockUnlockFunc *) \
+ QEMU_GENERIC(x, \
+ (QemuMutex *, qemu_mutex_unlock), \
+ (CoMutex *, qemu_co_mutex_unlock), \
+ (QemuSpin *, qemu_spin_unlock), \
+ unknown_lock_type))
+
+/* In C, compound literals have the lifetime of an automatic variable.
+ * In C++ it would be different, but then C++ wouldn't need QemuLockable
+ * either...
+ */
+#define QEMU_MAKE_LOCKABLE_(x) qemu_make_lockable((x), &(QemuLockable) { \
+ .object = (x), \
+ .lock = QEMU_LOCK_FUNC(x), \
+ .unlock = QEMU_UNLOCK_FUNC(x), \
+ })
+
+/* QEMU_MAKE_LOCKABLE - Make a polymorphic QemuLockable
+ *
+ * @x: a lock object (currently one of QemuMutex, CoMutex, QemuSpin).
+ *
+ * Returns a QemuLockable object that can be passed around
+ * to a function that can operate with locks of any kind.
+ */
+#define QEMU_MAKE_LOCKABLE(x) \
+ QEMU_GENERIC(x, \
+ (QemuLockable *, (x)), \
+ QEMU_MAKE_LOCKABLE_(x))
+
+static inline void qemu_lockable_lock(QemuLockable *x)
+{
+ x->lock(x->object);
+}
+
+static inline void qemu_lockable_unlock(QemuLockable *x)
+{
+ x->unlock(x->object);
+}
+
+#endif
diff --git a/include/qemu/thread.h b/include/qemu/thread.h
index 9af4e945aa..ef7bd16123 100644
--- a/include/qemu/thread.h
+++ b/include/qemu/thread.h
@@ -4,7 +4,6 @@
#include "qemu/processor.h"
#include "qemu/atomic.h"
-typedef struct QemuMutex QemuMutex;
typedef struct QemuCond QemuCond;
typedef struct QemuSemaphore QemuSemaphore;
typedef struct QemuEvent QemuEvent;
@@ -97,9 +96,9 @@ struct Notifier;
void qemu_thread_atexit_add(struct Notifier *notifier);
void qemu_thread_atexit_remove(struct Notifier *notifier);
-typedef struct QemuSpin {
+struct QemuSpin {
int value;
-} QemuSpin;
+};
static inline void qemu_spin_init(QemuSpin *spin)
{
diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
index 9bd7a834ba..5923849cdd 100644
--- a/include/qemu/typedefs.h
+++ b/include/qemu/typedefs.h
@@ -19,6 +19,7 @@ typedef struct BusClass BusClass;
typedef struct BusState BusState;
typedef struct Chardev Chardev;
typedef struct CompatProperty CompatProperty;
+typedef struct CoMutex CoMutex;
typedef struct CPUAddressSpace CPUAddressSpace;
typedef struct CPUState CPUState;
typedef struct DeviceListener DeviceListener;
@@ -86,9 +87,12 @@ typedef struct QEMUBH QEMUBH;
typedef struct QemuConsole QemuConsole;
typedef struct QemuDmaBuf QemuDmaBuf;
typedef struct QEMUFile QEMUFile;
+typedef struct QemuLockable QemuLockable;
+typedef struct QemuMutex QemuMutex;
typedef struct QemuOpt QemuOpt;
typedef struct QemuOpts QemuOpts;
typedef struct QemuOptsList QemuOptsList;
+typedef struct QemuSpin QemuSpin;
typedef struct QEMUSGList QEMUSGList;
typedef struct QEMUTimer QEMUTimer;
typedef struct QEMUTimerListGroup QEMUTimerListGroup;
diff --git a/tests/test-coroutine.c b/tests/test-coroutine.c
index 010cb95ad6..6e4842bfda 100644
--- a/tests/test-coroutine.c
+++ b/tests/test-coroutine.c
@@ -14,6 +14,7 @@
#include "qemu/osdep.h"
#include "qemu/coroutine.h"
#include "qemu/coroutine_int.h"
+#include "qemu/lockable.h"
/*
* Check that qemu_in_coroutine() works
@@ -210,6 +211,18 @@ static void coroutine_fn mutex_fn(void *opaque)
done++;
}
+static void coroutine_fn lockable_fn(void *opaque)
+{
+ QemuLockable *x = opaque;
+ qemu_lockable_lock(x);
+ assert(!locked);
+ locked = true;
+ qemu_coroutine_yield();
+ locked = false;
+ qemu_lockable_unlock(x);
+ done++;
+}
+
static void do_test_co_mutex(CoroutineEntry *entry, void *opaque)
{
Coroutine *c1 = qemu_coroutine_create(entry, opaque);
@@ -240,6 +253,17 @@ static void test_co_mutex(void)
do_test_co_mutex(mutex_fn, &m);
}
+static void test_co_mutex_lockable(void)
+{
+ CoMutex m;
+ CoMutex *null_pointer = NULL;
+
+ qemu_co_mutex_init(&m);
+ do_test_co_mutex(lockable_fn, QEMU_MAKE_LOCKABLE(&m));
+
+ g_assert(QEMU_MAKE_LOCKABLE(null_pointer) == NULL);
+}
+
/*
* Check that creation, enter, and return work
*/
@@ -478,6 +502,7 @@ int main(int argc, char **argv)
g_test_add_func("/basic/in_coroutine", test_in_coroutine);
g_test_add_func("/basic/order", test_order);
g_test_add_func("/locking/co-mutex", test_co_mutex);
+ g_test_add_func("/locking/co-mutex/lockable", test_co_mutex_lockable);
if (g_test_perf()) {
g_test_add_func("/perf/lifecycle", perf_lifecycle);
g_test_add_func("/perf/nesting", perf_nesting);
--
2.14.3
