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[Qemu-devel] [PULL 08/17] qemu-thread: add QemuEvent
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PULL 08/17] qemu-thread: add QemuEvent |
Date: |
Thu, 17 Oct 2013 17:48:46 +0200 |
This emulates Win32 manual-reset events using futexes or conditional
variables. Typical ways to use them are with multi-producer,
single-consumer data structures, to test for a complex condition whose
elements come from different threads:
for (;;) {
qemu_event_reset(ev);
... test complex condition ...
if (condition is true) {
break;
}
qemu_event_wait(ev);
}
Or more efficiently (but with some duplication):
... evaluate condition ...
while (!condition) {
qemu_event_reset(ev);
... evaluate condition ...
if (!condition) {
qemu_event_wait(ev);
... evaluate condition ...
}
}
QemuEvent provides a very fast userspace path in the common case when
no other thread is waiting, or the event is not changing state.
Signed-off-by: Paolo Bonzini <address@hidden>
---
include/qemu/thread-posix.h | 8 +++
include/qemu/thread-win32.h | 4 ++
include/qemu/thread.h | 7 +++
util/qemu-thread-posix.c | 116 ++++++++++++++++++++++++++++++++++++++++++++
util/qemu-thread-win32.c | 26 ++++++++++
5 files changed, 161 insertions(+)
diff --git a/include/qemu/thread-posix.h b/include/qemu/thread-posix.h
index 361566a..eb5c7a1 100644
--- a/include/qemu/thread-posix.h
+++ b/include/qemu/thread-posix.h
@@ -21,6 +21,14 @@ struct QemuSemaphore {
#endif
};
+struct QemuEvent {
+#ifndef __linux__
+ pthread_mutex_t lock;
+ pthread_cond_t cond;
+#endif
+ unsigned value;
+};
+
struct QemuThread {
pthread_t thread;
};
diff --git a/include/qemu/thread-win32.h b/include/qemu/thread-win32.h
index 13adb95..3d58081 100644
--- a/include/qemu/thread-win32.h
+++ b/include/qemu/thread-win32.h
@@ -17,6 +17,10 @@ struct QemuSemaphore {
HANDLE sema;
};
+struct QemuEvent {
+ HANDLE event;
+};
+
typedef struct QemuThreadData QemuThreadData;
struct QemuThread {
QemuThreadData *data;
diff --git a/include/qemu/thread.h b/include/qemu/thread.h
index c02404b..3e32c65 100644
--- a/include/qemu/thread.h
+++ b/include/qemu/thread.h
@@ -7,6 +7,7 @@
typedef struct QemuMutex QemuMutex;
typedef struct QemuCond QemuCond;
typedef struct QemuSemaphore QemuSemaphore;
+typedef struct QemuEvent QemuEvent;
typedef struct QemuThread QemuThread;
#ifdef _WIN32
@@ -45,6 +46,12 @@ void qemu_sem_wait(QemuSemaphore *sem);
int qemu_sem_timedwait(QemuSemaphore *sem, int ms);
void qemu_sem_destroy(QemuSemaphore *sem);
+void qemu_event_init(QemuEvent *ev, bool init);
+void qemu_event_set(QemuEvent *ev);
+void qemu_event_reset(QemuEvent *ev);
+void qemu_event_wait(QemuEvent *ev);
+void qemu_event_destroy(QemuEvent *ev);
+
void qemu_thread_create(QemuThread *thread,
void *(*start_routine)(void *),
void *arg, int mode);
diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
index 4de133e..37dd298 100644
--- a/util/qemu-thread-posix.c
+++ b/util/qemu-thread-posix.c
@@ -20,7 +20,12 @@
#include <limits.h>
#include <unistd.h>
#include <sys/time.h>
+#ifdef __linux__
+#include <sys/syscall.h>
+#include <linux/futex.h>
+#endif
#include "qemu/thread.h"
+#include "qemu/atomic.h"
static void error_exit(int err, const char *msg)
{
@@ -272,6 +277,117 @@ void qemu_sem_wait(QemuSemaphore *sem)
#endif
}
+#ifdef __linux__
+#define futex(...) syscall(__NR_futex, __VA_ARGS__)
+
+static inline void futex_wake(QemuEvent *ev, int n)
+{
+ futex(ev, FUTEX_WAKE, n, NULL, NULL, 0);
+}
+
+static inline void futex_wait(QemuEvent *ev, unsigned val)
+{
+ futex(ev, FUTEX_WAIT, (int) val, NULL, NULL, 0);
+}
+#else
+static inline void futex_wake(QemuEvent *ev, int n)
+{
+ if (n == 1) {
+ pthread_cond_signal(&ev->cond);
+ } else {
+ pthread_cond_broadcast(&ev->cond);
+ }
+}
+
+static inline void futex_wait(QemuEvent *ev, unsigned val)
+{
+ pthread_mutex_lock(&ev->lock);
+ if (ev->value == val) {
+ pthread_cond_wait(&ev->cond, &ev->lock);
+ }
+ pthread_mutex_unlock(&ev->lock);
+}
+#endif
+
+/* Valid transitions:
+ * - free->set, when setting the event
+ * - busy->set, when setting the event, followed by futex_wake
+ * - set->free, when resetting the event
+ * - free->busy, when waiting
+ *
+ * set->busy does not happen (it can be observed from the outside but
+ * it really is set->free->busy).
+ *
+ * busy->free provably cannot happen; to enforce it, the set->free transition
+ * is done with an OR, which becomes a no-op if the event has concurrently
+ * transitioned to free or busy.
+ */
+
+#define EV_SET 0
+#define EV_FREE 1
+#define EV_BUSY -1
+
+void qemu_event_init(QemuEvent *ev, bool init)
+{
+#ifndef __linux__
+ pthread_mutex_init(&ev->lock, NULL);
+ pthread_cond_init(&ev->cond, NULL);
+#endif
+
+ ev->value = (init ? EV_SET : EV_FREE);
+}
+
+void qemu_event_destroy(QemuEvent *ev)
+{
+#ifndef __linux__
+ pthread_mutex_destroy(&ev->lock);
+ pthread_cond_destroy(&ev->cond);
+#endif
+}
+
+void qemu_event_set(QemuEvent *ev)
+{
+ if (atomic_mb_read(&ev->value) != EV_SET) {
+ if (atomic_xchg(&ev->value, EV_SET) == EV_BUSY) {
+ /* There were waiters, wake them up. */
+ futex_wake(ev, INT_MAX);
+ }
+ }
+}
+
+void qemu_event_reset(QemuEvent *ev)
+{
+ if (atomic_mb_read(&ev->value) == EV_SET) {
+ /*
+ * If there was a concurrent reset (or even reset+wait),
+ * do nothing. Otherwise change EV_SET->EV_FREE.
+ */
+ atomic_or(&ev->value, EV_FREE);
+ }
+}
+
+void qemu_event_wait(QemuEvent *ev)
+{
+ unsigned value;
+
+ value = atomic_mb_read(&ev->value);
+ if (value != EV_SET) {
+ if (value == EV_FREE) {
+ /*
+ * Leave the event reset and tell qemu_event_set that there
+ * are waiters. No need to retry, because there cannot be
+ * a concurent busy->free transition. After the CAS, the
+ * event will be either set or busy.
+ */
+ if (atomic_cmpxchg(&ev->value, EV_FREE, EV_BUSY) == EV_SET) {
+ return;
+ }
+ }
+ futex_wait(ev, EV_BUSY);
+ }
+}
+
+
void qemu_thread_create(QemuThread *thread,
void *(*start_routine)(void*),
void *arg, int mode)
diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
index 517878d..27a5217 100644
--- a/util/qemu-thread-win32.c
+++ b/util/qemu-thread-win32.c
@@ -227,6 +227,32 @@ void qemu_sem_wait(QemuSemaphore *sem)
}
}
+void qemu_event_init(QemuEvent *ev, bool init)
+{
+ /* Manual reset. */
+ ev->event = CreateEvent(NULL, TRUE, init, NULL);
+}
+
+void qemu_event_destroy(QemuEvent *ev)
+{
+ CloseHandle(ev->event);
+}
+
+void qemu_event_set(QemuEvent *ev)
+{
+ SetEvent(ev->event);
+}
+
+void qemu_event_reset(QemuEvent *ev)
+{
+ ResetEvent(ev->event);
+}
+
+void qemu_event_wait(QemuEvent *ev)
+{
+ WaitForSingleObject(ev->event, INFINITE);
+}
+
struct QemuThreadData {
/* Passed to win32_start_routine. */
void *(*start_routine)(void *);
--
1.8.3.1
- [Qemu-devel] [PULL 00/17] Memory/threading changes for 1.7, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 01/17] memory: fix 128 arithmetic in info mtree, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 02/17] compatfd: switch to QemuThread, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 04/17] cirrus: Mark vga io region as coalesced MMIO flushing, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 05/17] vga: Mark relevant portio lists regions as coalesced MMIO flushing, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 03/17] portio: Allow to mark portio lists as coalesced MMIO flushing, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 10/17] timer: extract timer_mod_ns_locked and timerlist_rearm, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 11/17] timer: add timer_mod_anticipate and timer_mod_anticipate_ns, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 07/17] timer: protect timers_state's clock with seqlock, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 06/17] seqlock: introduce read-write seqlock, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 08/17] qemu-thread: add QemuEvent,
Paolo Bonzini <=
- [Qemu-devel] [PULL 12/17] icount: use cpu_get_icount() directly, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 09/17] timer: make qemu_clock_enable sync between disable and timer's cb, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 15/17] icount: document (future) locking rules for icount, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 13/17] icount: reorganize icount_warp_rt, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 14/17] icount: prepare the code for future races in calling qemu_clock_warp, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 16/17] icount: make it thread-safe, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 17/17] exec: remove qemu_safe_ram_ptr, Paolo Bonzini, 2013/10/17