4 files changed, 92 insertions, 6 deletions
diff --git a/absl/base/internal/errno_saver.h b/absl/base/internal/errno_saver.h
new file mode 100644
index 0000000..251de51
--- /dev/null
+++ b/absl/base/internal/errno_saver.h
@@ -0,0 +1,43 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_BASE_INTERNAL_ERRNO_SAVER_H_
+#define ABSL_BASE_INTERNAL_ERRNO_SAVER_H_
+
+#include <cerrno>
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+// `ErrnoSaver` captures the value of `errno` upon construction and restores it
+// upon deletion.  It is used in low-level code and must be super fast.  Do not
+// add instrumentation, even in debug modes.
+class ErrnoSaver {
+ public:
+  ErrnoSaver() : saved_errno_(errno) {}
+  ~ErrnoSaver() { errno = saved_errno_; }
+  int operator()() const { return saved_errno_; }
+
+ private:
+  const int saved_errno_;
+};
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_ERRNO_SAVER_H_
diff --git a/absl/base/internal/errno_saver_test.cc b/absl/base/internal/errno_saver_test.cc
new file mode 100644
index 0000000..b845e2d
--- /dev/null
+++ b/absl/base/internal/errno_saver_test.cc
@@ -0,0 +1,44 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/base/internal/errno_saver.h"
+
+#include <cerrno>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+namespace {
+using ::testing::Eq;
+
+struct ErrnoPrinter {
+  int no;
+};
+std::ostream &operator<<(std::ostream &os, ErrnoPrinter ep) {
+  return os << strerror(ep.no) << " [" << ep.no << "]";
+}
+bool operator==(ErrnoPrinter one, ErrnoPrinter two) { return one.no == two.no; }
+
+TEST(ErrnoSaverTest, Works) {
+  errno = EDOM;
+  {
+    absl::base_internal::ErrnoSaver errno_saver;
+    EXPECT_THAT(ErrnoPrinter{errno}, Eq(ErrnoPrinter{EDOM}));
+    errno = ERANGE;
+    EXPECT_THAT(ErrnoPrinter{errno}, Eq(ErrnoPrinter{ERANGE}));
+    EXPECT_THAT(ErrnoPrinter{errno_saver()}, Eq(ErrnoPrinter{EDOM}));
+  }
+  EXPECT_THAT(ErrnoPrinter{errno}, Eq(ErrnoPrinter{EDOM}));
+}
+}  // namespace
diff --git a/absl/base/internal/spinlock_linux.inc b/absl/base/internal/spinlock_linux.inc
index 28e29d1..323edd6 100644
--- a/absl/base/internal/spinlock_linux.inc
+++ b/absl/base/internal/spinlock_linux.inc
@@ -19,12 +19,12 @@
 #include <unistd.h>
 
 #include <atomic>
-#include <cerrno>
 #include <climits>
 #include <cstdint>
 #include <ctime>
 
 #include "absl/base/attributes.h"
+#include "absl/base/internal/errno_saver.h"
 
 // The SpinLock lockword is `std::atomic<uint32_t>`. Here we assert that
 // `std::atomic<uint32_t>` is bitwise equivalent of the `int` expected
@@ -51,12 +51,11 @@ extern "C" {
 ABSL_ATTRIBUTE_WEAK void AbslInternalSpinLockDelay(
     std::atomic<uint32_t> *w, uint32_t value, int loop,
     absl::base_internal::SchedulingMode) {
-  int save_errno = errno;
+  absl::base_internal::ErrnoSaver errno_saver;
   struct timespec tm;
   tm.tv_sec = 0;
   tm.tv_nsec = absl::base_internal::SpinLockSuggestedDelayNS(loop);
   syscall(SYS_futex, w, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, value, &tm);
-  errno = save_errno;
 }
 
 ABSL_ATTRIBUTE_WEAK void AbslInternalSpinLockWake(std::atomic<uint32_t> *w,
diff --git a/absl/base/internal/spinlock_posix.inc b/absl/base/internal/spinlock_posix.inc
index f025b5f..fcd21b1 100644
--- a/absl/base/internal/spinlock_posix.inc
+++ b/absl/base/internal/spinlock_posix.inc
@@ -15,10 +15,11 @@
 // This file is a Posix-specific part of spinlock_wait.cc
 
 #include <sched.h>
+
 #include <atomic>
 #include <ctime>
-#include <cerrno>
 
+#include "absl/base/internal/errno_saver.h"
 #include "absl/base/internal/scheduling_mode.h"
 #include "absl/base/port.h"
 
@@ -27,7 +28,7 @@ extern "C" {
 ABSL_ATTRIBUTE_WEAK void AbslInternalSpinLockDelay(
     std::atomic<uint32_t>* /* lock_word */, uint32_t /* value */, int loop,
     absl::base_internal::SchedulingMode /* mode */) {
-  int save_errno = errno;
+  absl::base_internal::ErrnoSaver errno_saver;
   if (loop == 0) {
   } else if (loop == 1) {
     sched_yield();
@@ -37,7 +38,6 @@ ABSL_ATTRIBUTE_WEAK void AbslInternalSpinLockDelay(
     tm.tv_nsec = absl::base_internal::SpinLockSuggestedDelayNS(loop);
     nanosleep(&tm, nullptr);
   }
-  errno = save_errno;
 }
 
 ABSL_ATTRIBUTE_WEAK void AbslInternalSpinLockWake(