ui/progress: Restore atomics in Counter

We switched from atomics to a mutex in #3189 because of an alignment
bug, but the new-style atomic types don't need manual alignment.

internal/ui/progress/counter.go

@@ -1,7 +1,7 @@
 package progress
 
 import (
-	"sync"
+	"sync/atomic"
 	"time"
 )
 
@@ -17,17 +17,13 @@ type Func func(value uint64, total uint64, runtime time.Duration, final bool)
 // The Func is also called when SIGUSR1 (or SIGINFO, on BSD) is received.
 type Counter struct {
 	Updater
-
+	value, max atomic.Uint64
-	valueMutex sync.Mutex
-	value      uint64
-	max        uint64
 }
 
 // NewCounter starts a new Counter.
 func NewCounter(interval time.Duration, total uint64, report Func) *Counter {
-	c := &Counter{
+	c := new(Counter)
-		max: total,
+	c.max.Store(total)
-	}
 	c.Updater = *NewUpdater(interval, func(runtime time.Duration, final bool) {
 		v, maxV := c.Get()
 		report(v, maxV, runtime, final)
@@ -37,33 +33,22 @@ func NewCounter(interval time.Duration, total uint64, report Func) *Counter {
 
 // Add v to the Counter. This method is concurrency-safe.
 func (c *Counter) Add(v uint64) {
-	if c == nil {
+	if c != nil {
-		return
+		c.value.Add(v)
 	}
-
-	c.valueMutex.Lock()
-	c.value += v
-	c.valueMutex.Unlock()
 }
 
 // SetMax sets the maximum expected counter value. This method is concurrency-safe.
 func (c *Counter) SetMax(max uint64) {
-	if c == nil {
+	if c != nil {
-		return
+		c.max.Store(max)
 	}
-	c.valueMutex.Lock()
-	c.max = max
-	c.valueMutex.Unlock()
 }
 
 // Get returns the current value and the maximum of c.
 // This method is concurrency-safe.
 func (c *Counter) Get() (v, max uint64) {
-	c.valueMutex.Lock()
+	return c.value.Load(), c.max.Load()
-	v, max = c.value, c.max
-	c.valueMutex.Unlock()
-
-	return v, max
 }
 
 func (c *Counter) Done() {