MEDIUM: threads/freq_ctr: Make the frequency counters thread-safe
When a frequency counter must be updated, we use the curr_sec/curr_tick fields
as a lock, by setting the MSB to 1 in a compare-and-swap to lock and by reseting
it to unlock. And when we need to read it, we loop until the counter is
unlocked. This way, the frequency counters are thread-safe without any external
lock. It is important to avoid increasing the size of many structures (global,
proxy, server, stick_table).
diff --git a/src/freq_ctr.c b/src/freq_ctr.c
index 6dec970..37fb1f3 100644
--- a/src/freq_ctr.c
+++ b/src/freq_ctr.c
@@ -31,17 +31,25 @@
unsigned int read_freq_ctr(struct freq_ctr *ctr)
{
unsigned int curr, past;
- unsigned int age;
+ unsigned int age, curr_sec;
- age = now.tv_sec - ctr->curr_sec;
+ do {
+ curr = ctr->curr_ctr;
+ past = ctr->prev_ctr;
+ curr_sec = ctr->curr_sec;
+
+ } while (curr != ctr->curr_ctr
+ || past != ctr->prev_ctr
+ || curr_sec != ctr->curr_sec
+ || (curr_sec & 0x80000000));
+
+ age = now.tv_sec - curr_sec;
if (unlikely(age > 1))
return 0;
- curr = 0;
- past = ctr->curr_ctr;
- if (likely(!age)) {
- curr = past;
- past = ctr->prev_ctr;
+ if (unlikely(age)) {
+ past = curr;
+ curr = 0;
}
if (past <= 1 && !curr)
@@ -57,16 +65,25 @@
unsigned int freq_ctr_remain(struct freq_ctr *ctr, unsigned int freq, unsigned int pend)
{
unsigned int curr, past;
- unsigned int age;
+ unsigned int age, curr_sec;
+
+ do {
+ curr = ctr->curr_ctr;
+ past = ctr->prev_ctr;
+ curr_sec = ctr->curr_sec;
- curr = 0;
- age = now.tv_sec - ctr->curr_sec;
+ } while (curr != ctr->curr_ctr
+ || past != ctr->prev_ctr
+ || curr_sec != ctr->curr_sec
+ || (curr_sec & 0x80000000));
- if (likely(age <= 1)) {
- past = ctr->curr_ctr;
- if (likely(!age)) {
- curr = past;
- past = ctr->prev_ctr;
+ age = now.tv_sec - curr_sec;
+ if (unlikely(age > 1))
+ curr = 0;
+ else {
+ if (unlikely(age == 1)) {
+ past = curr;
+ curr = 0;
}
curr += mul32hi(past, ms_left_scaled);
}
@@ -86,17 +103,25 @@
unsigned int next_event_delay(struct freq_ctr *ctr, unsigned int freq, unsigned int pend)
{
unsigned int curr, past;
- unsigned int wait, age;
+ unsigned int wait, age, curr_sec;
+
+ do {
+ curr = ctr->curr_ctr;
+ past = ctr->prev_ctr;
+ curr_sec = ctr->curr_sec;
- past = 0;
- curr = 0;
- age = now.tv_sec - ctr->curr_sec;
+ } while (curr != ctr->curr_ctr
+ || past != ctr->prev_ctr
+ || curr_sec != ctr->curr_sec
+ || (curr_sec & 0x80000000));
- if (likely(age <= 1)) {
- past = ctr->curr_ctr;
- if (likely(!age)) {
- curr = past;
- past = ctr->prev_ctr;
+ age = now.tv_sec - curr_sec;
+ if (unlikely(age > 1))
+ curr = 0;
+ else {
+ if (unlikely(age == 1)) {
+ past = curr;
+ curr = 0;
}
curr += mul32hi(past, ms_left_scaled);
}
@@ -128,12 +153,19 @@
unsigned int read_freq_ctr_period(struct freq_ctr_period *ctr, unsigned int period)
{
unsigned int curr, past;
- unsigned int remain;
+ unsigned int remain, curr_tick;
- curr = ctr->curr_ctr;
- past = ctr->prev_ctr;
+ do {
+ curr = ctr->curr_ctr;
+ past = ctr->prev_ctr;
+ curr_tick = ctr->curr_tick;
+
+ } while (curr != ctr->curr_ctr
+ || past != ctr->prev_ctr
+ || curr_tick != ctr->curr_tick
+ || (curr_tick & 0x1));
- remain = ctr->curr_tick + period - now_ms;
+ remain = curr_tick + period - now_ms;
if (unlikely((int)remain < 0)) {
/* We're past the first period, check if we can still report a
* part of last period or if we're too far away.
@@ -159,12 +191,19 @@
unsigned int freq, unsigned int pend)
{
unsigned int curr, past;
- unsigned int remain;
+ unsigned int remain, curr_tick;
- curr = ctr->curr_ctr;
- past = ctr->prev_ctr;
+ do {
+ curr = ctr->curr_ctr;
+ past = ctr->prev_ctr;
+ curr_tick = ctr->curr_tick;
+
+ } while (curr != ctr->curr_ctr
+ || past != ctr->prev_ctr
+ || curr_tick != ctr->curr_tick
+ || (curr_tick & 0x1));
- remain = ctr->curr_tick + period - now_ms;
+ remain = curr_tick + period - now_ms;
if (likely((int)remain < 0)) {
/* We're past the first period, check if we can still report a
* part of last period or if we're too far away.