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

[Rémi Denis-Courmont]

---
 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