[vlc-devel] [PATCH 1/7] posix: add fallback vlc_atomic_* implementation

[Rémi Denis-Courmont]

The clock is mixed up between real-time and monotonic here.

Le 16 février 2020 19:50:40 GMT+02:00, "Rémi Denis-Courmont" <remi at remlab.net> a écrit :
>---
> src/Makefile.am  |   3 ++
> src/posix/wait.c | 128 +++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 131 insertions(+)
> create mode 100644 src/posix/wait.c
>
>diff --git a/src/Makefile.am b/src/Makefile.am
>index f2adf61095..0ad47fc105 100644
>--- a/src/Makefile.am
>+++ b/src/Makefile.am
>@@ -482,6 +482,9 @@ libvlccore_la_SOURCES += \
> 	posix/plugin.c \
> 	posix/rand.c \
> 	posix/timer.c
>+if !HAVE_LINUX
>+libvlccore_la_SOURCES += posix/wait.c
>+endif
> if !HAVE_ANDROID
> libvlccore_la_SOURCES += posix/sort.c
> if !HAVE_DARWIN
>diff --git a/src/posix/wait.c b/src/posix/wait.c
>new file mode 100644
>index 0000000000..60f9c7626f
>--- /dev/null
>+++ b/src/posix/wait.c
>@@ -0,0 +1,128 @@
>+/*****************************************************************************
>+ * wait.c : pthread back-end for vlc_atomic_wait
>+
>*****************************************************************************
>+ * Copyright (C) 2019-2020 Rémi Denis-Courmont
>+ *
>+ * This program 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.
>+ *
>+ * This program 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 this program; if not, write to the Free Software
>Foundation,
>+ * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
>+
>*****************************************************************************/
>+
>+#ifdef HAVE_CONFIG_H
>+# include "config.h"
>+#endif
>+
>+#include <vlc_common.h>
>+
>+#include <stdalign.h>
>+#include <stdatomic.h>
>+#include <errno.h>
>+#include <time.h>
>+
>+#include <sys/types.h>
>+#include <pthread.h>
>+
>+#define WAIT_BUCKET_INIT \
>+     { PTHREAD_MUTEX_INITIALIZER, PTHREAD_COND_INITIALIZER, 0 }
>+#define WAIT_BUCKET_INIT_2 WAIT_BUCKET_INIT, WAIT_BUCKET_INIT
>+#define WAIT_BUCKET_INIT_4 WAIT_BUCKET_INIT_2, WAIT_BUCKET_INIT_2
>+#define WAIT_BUCKET_INIT_8 WAIT_BUCKET_INIT_4, WAIT_BUCKET_INIT_4
>+#define WAIT_BUCKET_INIT_16 WAIT_BUCKET_INIT_8, WAIT_BUCKET_INIT_8
>+#define WAIT_BUCKET_INIT_32 WAIT_BUCKET_INIT_16, WAIT_BUCKET_INIT_16
>+
>+static struct wait_bucket
>+{
>+    pthread_mutex_t lock;
>+    pthread_cond_t wait;
>+    unsigned waiters;
>+} wait_buckets[32] = { WAIT_BUCKET_INIT_32 };
>+
>+static struct wait_bucket *wait_bucket_get(atomic_uint *addr)
>+{
>+    uintptr_t u = (uintptr_t)addr;
>+    size_t idx = (u / alignof (*addr)) % ARRAY_SIZE(wait_buckets);
>+
>+    return &wait_buckets[idx];
>+}
>+
>+static struct wait_bucket *wait_bucket_enter(atomic_uint *addr)
>+{
>+    struct wait_bucket *bucket = wait_bucket_get(addr);
>+
>+    pthread_mutex_lock(&bucket->lock);
>+    bucket->waiters++;
>+    return bucket;
>+}
>+
>+static void wait_bucket_leave(void *data)
>+{
>+    struct wait_bucket *bucket = data;
>+
>+    bucket->waiters--;
>+    pthread_mutex_unlock(&bucket->lock);
>+}
>+
>+void vlc_atomic_wait(void *addr, unsigned value)
>+{
>+    atomic_uint *futex = addr;
>+    struct wait_bucket *bucket = wait_bucket_enter(futex);
>+
>+    pthread_cleanup_push(wait_bucket_leave, bucket);
>+
>+    if (value == atomic_load_explicit(futex, memory_order_relaxed))
>+        pthread_cond_wait(&bucket->wait, &bucket->lock);
>+
>+    pthread_cleanup_pop(1);
>+}
>+
>+bool vlc_atomic_timedwait(void *addr, unsigned value, vlc_tick_t
>delay)
>+{
>+    atomic_uint *futex = addr;
>+    struct wait_bucket *bucket;
>+    struct timespec ts;
>+    lldiv_t d = lldiv(delay, CLOCK_FREQ);
>+    int ret = 0;
>+
>+    clock_gettime(CLOCK_MONOTONIC, &ts);
>+    ts.tv_sec += d.quot;
>+    ts.tv_nsec += NS_FROM_VLC_TICK(d.rem);
>+
>+    if (ts.tv_nsec >= 1000000000) {
>+        ts.tv_sec++;
>+        ts.tv_nsec -= 1000000000;
>+    }
>+
>+    bucket = wait_bucket_enter(futex);
>+    pthread_cleanup_push(wait_bucket_leave, bucket);
>+
>+    if (value == atomic_load_explicit(futex, memory_order_relaxed))
>+        ret = pthread_cond_timedwait(&bucket->wait, &bucket->lock,
>&ts);
>+
>+    pthread_cleanup_pop(1);
>+    return ret == 0;
>+}
>+
>+void vlc_atomic_notify_one(void *addr)
>+{
>+    vlc_atomic_notify_all(addr);
>+}
>+
>+void vlc_atomic_notify_all(void *addr)
>+{
>+    struct wait_bucket *bucket = wait_bucket_get(addr);
>+
>+    pthread_mutex_lock(&bucket->lock);
>+    if (bucket->waiters > 0)
>+        pthread_cond_broadcast(&bucket->wait);
>+    pthread_mutex_unlock(&bucket->lock);
>+}
>-- 
>2.25.0
>
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