100 lines
2.2 KiB
Go
100 lines
2.2 KiB
Go
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package xsync
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import (
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"sync"
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"sync/atomic"
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)
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// pool for P tokens
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var ptokenPool sync.Pool
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// a P token is used to point at the current OS thread (P)
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// on which the goroutine is run; exact identity of the thread,
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// as well as P migration tolerance, is not important since
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// it's used to as a best effort mechanism for assigning
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// concurrent operations (goroutines) to different stripes of
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// the counter
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type ptoken struct {
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idx uint32
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//lint:ignore U1000 prevents false sharing
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pad [cacheLineSize - 4]byte
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}
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// A Counter is a striped int64 counter.
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//
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// Should be preferred over a single atomically updated int64
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// counter in high contention scenarios.
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//
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// A Counter must not be copied after first use.
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type Counter struct {
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stripes []cstripe
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mask uint32
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}
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type cstripe struct {
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c int64
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//lint:ignore U1000 prevents false sharing
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pad [cacheLineSize - 8]byte
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}
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// NewCounter creates a new Counter instance.
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func NewCounter() *Counter {
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nstripes := nextPowOf2(parallelism())
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c := Counter{
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stripes: make([]cstripe, nstripes),
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mask: nstripes - 1,
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}
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return &c
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}
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// Inc increments the counter by 1.
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func (c *Counter) Inc() {
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c.Add(1)
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}
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// Dec decrements the counter by 1.
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func (c *Counter) Dec() {
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c.Add(-1)
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}
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// Add adds the delta to the counter.
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func (c *Counter) Add(delta int64) {
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t, ok := ptokenPool.Get().(*ptoken)
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if !ok {
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t = new(ptoken)
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t.idx = runtime_fastrand()
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}
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for {
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stripe := &c.stripes[t.idx&c.mask]
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cnt := atomic.LoadInt64(&stripe.c)
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if atomic.CompareAndSwapInt64(&stripe.c, cnt, cnt+delta) {
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break
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}
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// Give a try with another randomly selected stripe.
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t.idx = runtime_fastrand()
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}
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ptokenPool.Put(t)
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}
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// Value returns the current counter value.
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// The returned value may not include all of the latest operations in
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// presence of concurrent modifications of the counter.
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func (c *Counter) Value() int64 {
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v := int64(0)
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for i := 0; i < len(c.stripes); i++ {
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stripe := &c.stripes[i]
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v += atomic.LoadInt64(&stripe.c)
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}
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return v
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}
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// Reset resets the counter to zero.
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// This method should only be used when it is known that there are
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// no concurrent modifications of the counter.
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func (c *Counter) Reset() {
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for i := 0; i < len(c.stripes); i++ {
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stripe := &c.stripes[i]
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atomic.StoreInt64(&stripe.c, 0)
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}
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}
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