Implemented rate limiter.

Fixes #12.

1 files changed, 108 insertions, 0 deletions

diff --git a/src/rate_limiter.c b/src/rate_limiter.c
new file mode 100644
index 0000000..d1c701a
--- /dev/null
+++ b/src/rate_limiter.c
@@ -0,0 +1,108 @@
+/*
+    Copyright 2014 Martin Pärtel <martin.partel@gmail.com>
+
+    This file is part of bindfs.
+
+    bindfs is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 2 of the License, or
+    (at your option) any later version.
+
+    bindfs 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 General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with bindfs.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#define _POSIX_C_SOURCE 199309L  /* for nanosleep() */
+
+#include "rate_limiter.h"
+#include <assert.h>
+#include <errno.h>
+#include <pthread.h>
+#include <time.h>
+#include <sys/time.h>
+
+const double rate_limiter_idle_credit = -0.2;
+
+double gettimeofday_clock()
+{
+    struct timeval tv;
+    gettimeofday(&tv, NULL);
+    return tv.tv_sec + tv.tv_usec * 0.000001;
+}
+
+static void sleep_seconds(double s)
+{
+    struct timespec ts;
+    ts.tv_sec = (time_t)s;
+    ts.tv_nsec = (long)((s - ts.tv_sec) * 1000000000L);
+    /* Guard against float imprecision */
+    if (ts.tv_nsec > 999999999L) {
+        ts.tv_nsec = 999999999L;
+    } else if (ts.tv_nsec < 0L) {
+        ts.tv_nsec = 0L;
+    }
+
+    nanosleep(&ts, NULL);
+}
+
+void rate_limiter_init(RateLimiter *limiter, double rate, double (*clock)())
+{
+    limiter->rate = rate;
+    limiter->clock = clock;
+    limiter->last_modified = limiter->clock();
+    limiter->accumulated_sleep_time = rate_limiter_idle_credit;
+
+    pthread_mutexattr_t attr;
+    int status = pthread_mutexattr_init(&attr);
+    assert(status == 0);
+    status = pthread_mutex_init(&limiter->mutex, &attr);
+    assert(status == 0);
+    status = pthread_mutexattr_destroy(&attr);
+    assert(status == 0);
+}
+
+void rate_limiter_wait(RateLimiter* limiter, size_t size)
+{
+    double time_to_sleep = rate_limiter_wait_nosleep(limiter, size);
+    sleep_seconds(time_to_sleep);
+}
+
+double rate_limiter_wait_nosleep(RateLimiter* limiter, size_t size)
+{
+    int status = pthread_mutex_lock(&limiter->mutex);
+    assert(status == 0);
+
+    double time_to_add = size / limiter->rate;
+
+    double now = limiter->clock();
+    double elapsed = now - limiter->last_modified;
+    if (elapsed < 0) {
+        elapsed = 0;
+    }
+
+    double time_to_sleep = limiter->accumulated_sleep_time;
+    time_to_sleep -= elapsed;
+    if (time_to_sleep < rate_limiter_idle_credit) {
+        time_to_sleep = rate_limiter_idle_credit;
+    }
+    time_to_sleep += time_to_add;
+    limiter->accumulated_sleep_time = time_to_sleep;
+
+    limiter->last_modified = now;
+
+    status = pthread_mutex_unlock(&limiter->mutex);
+    assert(status == 0);
+
+    return time_to_sleep;
+}
+
+void rate_limiter_destroy(RateLimiter *limiter)
+{
+    int status = pthread_mutex_destroy(&limiter->mutex);
+    assert(status == 0);
+}