internal/poll: better panic message for lock overflow

Instead of "inconsistent poll.fdMutex", panic with
"too many concurrent operations on a single file or socket (max 1048575)".

Fixes #25558

Change-Id: I5cad3633aa539fb6f48cca236c6656c86acfb663
Reviewed-on: https://go-review.googlesource.com/119956
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Dmitry Vyukov <dvyukov@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

diff --git a/src/internal/poll/fd_mutex.go b/src/internal/poll/fd_mutex.go
index 2ba7de7da376b81a90c06d61e6ad3a86afb89d13..0a8ee6f0d49d5c205844bfd62771d6effa9a6e7f 100644 (file)
--- a/src/internal/poll/fd_mutex.go
+++ b/src/internal/poll/fd_mutex.go
@@ -34,6 +34,8 @@ const (
        mutexWMask   = (1<<20 - 1) << 43
 )
 
+const overflowMsg = "too many concurrent operations on a single file or socket (max 1048575)"
+
 // Read operations must do rwlock(true)/rwunlock(true).
 //
 // Write operations must do rwlock(false)/rwunlock(false).
@@ -56,7 +58,7 @@ func (mu *fdMutex) incref() bool {
                }
                new := old + mutexRef
                if new&mutexRefMask == 0 {
-                       panic("inconsistent poll.fdMutex")
+                       panic(overflowMsg)
                }
                if atomic.CompareAndSwapUint64(&mu.state, old, new) {
                        return true
@@ -75,7 +77,7 @@ func (mu *fdMutex) increfAndClose() bool {
                // Mark as closed and acquire a reference.
                new := (old | mutexClosed) + mutexRef
                if new&mutexRefMask == 0 {
-                       panic("inconsistent poll.fdMutex")
+                       panic(overflowMsg)
                }
                // Remove all read and write waiters.
                new &^= mutexRMask | mutexWMask
@@ -136,13 +138,13 @@ func (mu *fdMutex) rwlock(read bool) bool {
                        // Lock is free, acquire it.
                        new = (old | mutexBit) + mutexRef
                        if new&mutexRefMask == 0 {
-                               panic("inconsistent poll.fdMutex")
+                               panic(overflowMsg)
                        }
                } else {
                        // Wait for lock.
                        new = old + mutexWait
                        if new&mutexMask == 0 {
-                               panic("inconsistent poll.fdMutex")
+                               panic(overflowMsg)
                        }
                }
                if atomic.CompareAndSwapUint64(&mu.state, old, new) {

diff --git a/src/internal/poll/fd_mutex_test.go b/src/internal/poll/fd_mutex_test.go
index bab81c6dfee53698b9a5660a7487ebc2c49c41d3..2c53c4561fbb73b956dd3539beb893290a501171 100644 (file)
--- a/src/internal/poll/fd_mutex_test.go
+++ b/src/internal/poll/fd_mutex_test.go
@@ -8,6 +8,7 @@ import (
        . "internal/poll"
        "math/rand"
        "runtime"
+       "strings"
        "testing"
        "time"
 )
@@ -121,6 +122,27 @@ func TestMutexPanic(t *testing.T) {
        mu.RWUnlock(false)
 }
 
+func TestMutexOverflowPanic(t *testing.T) {
+       defer func() {
+               r := recover()
+               if r == nil {
+                       t.Fatal("did not panic")
+               }
+               msg, ok := r.(string)
+               if !ok {
+                       t.Fatalf("unexpected panic type %T", r)
+               }
+               if !strings.Contains(msg, "too many") || strings.Contains(msg, "inconsistent") {
+                       t.Fatalf("wrong panic message %q", msg)
+               }
+       }()
+
+       var mu1 FDMutex
+       for i := 0; i < 1<<21; i++ {
+               mu1.Incref()
+       }
+}
+
 func TestMutexStress(t *testing.T) {
        P := 8
        N := int(1e6)