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sqlbase: avoid a race in sqlbase.CancelChecker #35548

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merged 1 commit into from
Mar 8, 2019
Merged

sqlbase: avoid a race in sqlbase.CancelChecker #35548

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14 changes: 10 additions & 4 deletions pkg/sql/sqlbase/cancel_checker.go
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,10 @@

package sqlbase

import "context"
import (
"context"
"sync/atomic"
)

// CancelChecker is a helper object for repeatedly checking whether the associated context
// has been canceled or not. Encapsulates all logic for waiting for cancelCheckInterval
Expand All @@ -25,7 +28,7 @@ type CancelChecker struct {
ctx context.Context

// Number of times Check() has been called since last context cancellation check.
callsSinceLastCheck int32
callsSinceLastCheck uint32
}

// NewCancelChecker returns a new CancelChecker.
Expand All @@ -42,7 +45,7 @@ func (c *CancelChecker) Check() error {
// bitwise AND instead of division.
const cancelCheckInterval = 1024

if c.callsSinceLastCheck%cancelCheckInterval == 0 {
if atomic.LoadUint32(&c.callsSinceLastCheck)%cancelCheckInterval == 0 {
select {
case <-c.ctx.Done():
// Once the context is canceled, we no longer increment
Expand All @@ -52,7 +55,10 @@ func (c *CancelChecker) Check() error {
default:
}
}
c.callsSinceLastCheck++

// Increment. This may rollover when the 32-bit capacity is reached,
// but that's all right.
atomic.AddUint32(&c.callsSinceLastCheck, 1)
return nil
}

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