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Commit 847d40d

Browse files
WillAbidesjba
authored andcommitted
log/slog: fix issue with concurrent writes
This causes instances commonHandler created by withAttrs or withGroup to share a mutex with their parent preventing concurrent writes to their shared writer. Fixes #61321 Change-Id: Ieec225e88ad51c84b41bad6c409fac48c90320b2 Reviewed-on: https://go-review.googlesource.com/c/go/+/509196 Reviewed-by: Bryan Mills <bcmills@google.com> TryBot-Result: Gopher Robot <gobot@golang.org> Run-TryBot: Jonathan Amsterdam <jba@google.com> Reviewed-by: Jonathan Amsterdam <jba@google.com>
1 parent c30faf9 commit 847d40d

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4 files changed

+53
-1
lines changed

4 files changed

+53
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lines changed

‎src/log/slog/handler.go‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -193,7 +193,7 @@ type commonHandler struct {
193193
groupPrefix string
194194
groups []string // all groups started from WithGroup
195195
nOpenGroups int // the number of groups opened in preformattedAttrs
196-
mu sync.Mutex
196+
mu *sync.Mutex
197197
w io.Writer
198198
}
199199

@@ -207,6 +207,7 @@ func (h *commonHandler) clone() *commonHandler {
207207
groups: slices.Clip(h.groups),
208208
nOpenGroups: h.nOpenGroups,
209209
w: h.w,
210+
mu: h.mu, // mutex shared among all clones of this handler
210211
}
211212
}
212213

‎src/log/slog/handler_test.go‎

Lines changed: 47 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -16,6 +16,7 @@ import (
1616
"slices"
1717
"strconv"
1818
"strings"
19+
"sync"
1920
"testing"
2021
"time"
2122
)
@@ -106,6 +107,52 @@ func TestDefaultHandle(t *testing.T) {
106107
}
107108
}
108109

110+
func TestConcurrentWrites(t *testing.T) {
111+
ctx := context.Background()
112+
count := 1000
113+
for _, handlerType := range []string{"text", "json"} {
114+
t.Run(handlerType, func(t *testing.T) {
115+
var buf bytes.Buffer
116+
var h Handler
117+
switch handlerType {
118+
case "text":
119+
h = NewTextHandler(&buf, nil)
120+
case "json":
121+
h = NewJSONHandler(&buf, nil)
122+
default:
123+
t.Fatalf("unexpected handlerType %q", handlerType)
124+
}
125+
sub1 := h.WithAttrs([]Attr{Bool("sub1", true)})
126+
sub2 := h.WithAttrs([]Attr{Bool("sub2", true)})
127+
var wg sync.WaitGroup
128+
for i := 0; i < count; i++ {
129+
sub1Record := NewRecord(time.Time{}, LevelInfo, "hello from sub1", 0)
130+
sub1Record.AddAttrs(Int("i", i))
131+
sub2Record := NewRecord(time.Time{}, LevelInfo, "hello from sub2", 0)
132+
sub2Record.AddAttrs(Int("i", i))
133+
wg.Add(1)
134+
go func() {
135+
defer wg.Done()
136+
if err := sub1.Handle(ctx, sub1Record); err != nil {
137+
t.Error(err)
138+
}
139+
if err := sub2.Handle(ctx, sub2Record); err != nil {
140+
t.Error(err)
141+
}
142+
}()
143+
}
144+
wg.Wait()
145+
for i := 1; i <= 2; i++ {
146+
want := "hello from sub" + strconv.Itoa(i)
147+
n := strings.Count(buf.String(), want)
148+
if n != count {
149+
t.Fatalf("want %d occurrences of %q, got %d", count, want, n)
150+
}
151+
}
152+
})
153+
}
154+
}
155+
109156
// Verify the common parts of TextHandler and JSONHandler.
110157
func TestJSONAndTextHandlers(t *testing.T) {
111158
// remove all Attrs

‎src/log/slog/json_handler.go‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -13,6 +13,7 @@ import (
1313
"io"
1414
"log/slog/internal/buffer"
1515
"strconv"
16+
"sync"
1617
"time"
1718
"unicode/utf8"
1819
)
@@ -35,6 +36,7 @@ func NewJSONHandler(w io.Writer, opts *HandlerOptions) *JSONHandler {
3536
json: true,
3637
w: w,
3738
opts: *opts,
39+
mu: &sync.Mutex{},
3840
},
3941
}
4042
}

‎src/log/slog/text_handler.go‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -11,6 +11,7 @@ import (
1111
"io"
1212
"reflect"
1313
"strconv"
14+
"sync"
1415
"unicode"
1516
"unicode/utf8"
1617
)
@@ -33,6 +34,7 @@ func NewTextHandler(w io.Writer, opts *HandlerOptions) *TextHandler {
3334
json: false,
3435
w: w,
3536
opts: *opts,
37+
mu: &sync.Mutex{},
3638
},
3739
}
3840
}

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