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129 lines
3.5 KiB
Go
129 lines
3.5 KiB
Go
package regexp2
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import (
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"sync"
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"sync/atomic"
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"time"
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)
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// fasttime holds a time value (ticks since clock initialization)
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type fasttime int64
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// fastclock provides a fast clock implementation.
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//
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// A background goroutine periodically stores the current time
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// into an atomic variable.
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//
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// A deadline can be quickly checked for expiration by comparing
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// its value to the clock stored in the atomic variable.
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//
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// The goroutine automatically stops once clockEnd is reached.
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// (clockEnd covers the largest deadline seen so far + some
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// extra time). This ensures that if regexp2 with timeouts
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// stops being used we will stop background work.
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type fastclock struct {
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// instances of atomicTime must be at the start of the struct (or at least 64-bit aligned)
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// otherwise 32-bit architectures will panic
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current atomicTime // Current time (approximate)
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clockEnd atomicTime // When clock updater is supposed to stop (>= any existing deadline)
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// current and clockEnd can be read via atomic loads.
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// Reads and writes of other fields require mu to be held.
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mu sync.Mutex
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start time.Time // Time corresponding to fasttime(0)
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running bool // Is a clock updater running?
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}
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var fast fastclock
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// reached returns true if current time is at or past t.
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func (t fasttime) reached() bool {
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return fast.current.read() >= t
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}
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// makeDeadline returns a time that is approximately time.Now().Add(d)
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func makeDeadline(d time.Duration) fasttime {
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// Increase the deadline since the clock we are reading may be
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// just about to tick forwards.
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end := fast.current.read() + durationToTicks(d+clockPeriod)
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// Start or extend clock if necessary.
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if end > fast.clockEnd.read() {
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extendClock(end)
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}
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return end
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}
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// extendClock ensures that clock is live and will run until at least end.
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func extendClock(end fasttime) {
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fast.mu.Lock()
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defer fast.mu.Unlock()
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if fast.start.IsZero() {
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fast.start = time.Now()
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}
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// Extend the running time to cover end as well as a bit of slop.
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if shutdown := end + durationToTicks(time.Second); shutdown > fast.clockEnd.read() {
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fast.clockEnd.write(shutdown)
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}
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// Start clock if necessary
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if !fast.running {
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fast.running = true
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go runClock()
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}
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}
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// stop the timeout clock in the background
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// should only used for unit tests to abandon the background goroutine
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func stopClock() {
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fast.mu.Lock()
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if fast.running {
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fast.clockEnd.write(fasttime(0))
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}
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fast.mu.Unlock()
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// pause until not running
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// get and release the lock
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isRunning := true
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for isRunning {
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time.Sleep(clockPeriod / 2)
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fast.mu.Lock()
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isRunning = fast.running
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fast.mu.Unlock()
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}
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}
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func durationToTicks(d time.Duration) fasttime {
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// Downscale nanoseconds to approximately a millisecond so that we can avoid
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// overflow even if the caller passes in math.MaxInt64.
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return fasttime(d) >> 20
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}
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const DefaultClockPeriod = 100 * time.Millisecond
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// clockPeriod is the approximate interval between updates of approximateClock.
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var clockPeriod = DefaultClockPeriod
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func runClock() {
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fast.mu.Lock()
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defer fast.mu.Unlock()
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for fast.current.read() <= fast.clockEnd.read() {
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// Unlock while sleeping.
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fast.mu.Unlock()
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time.Sleep(clockPeriod)
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fast.mu.Lock()
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newTime := durationToTicks(time.Since(fast.start))
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fast.current.write(newTime)
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}
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fast.running = false
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}
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type atomicTime struct{ v int64 } // Should change to atomic.Int64 when we can use go 1.19
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func (t *atomicTime) read() fasttime { return fasttime(atomic.LoadInt64(&t.v)) }
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func (t *atomicTime) write(v fasttime) { atomic.StoreInt64(&t.v, int64(v)) }
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