Bug 1804499 - [3/4] Expose stall-and-retry code beyond mozjemalloc.cpp r=glandium

Extract the stall-and-retry logic from mozjemalloc into a header. Write
a unit test for it.

Differential Revision: https://phabricator.services.mozilla.com/D164107

memory/build/moz.build

@@ -8,6 +8,7 @@ EXPORTS += [
     "malloc_decls.h",
     "mozjemalloc_types.h",
     "mozmemory.h",
+    "mozmemory_utils.h",
     "mozmemory_wrap.h",
 ]
 
@@ -60,3 +61,5 @@ if CONFIG["CC_TYPE"] == "clang-cl":
     AllowCompilerWarnings()  # workaround for bug 1090497
 
 REQUIRES_UNIFIED_BUILD = True
+
+TEST_DIRS += ["test"]

memory/build/mozjemalloc.cpp

@@ -164,8 +164,8 @@
 #include "Mutex.h"
 #include "Utils.h"
 
-// For GetGeckoProcessType(), when it's used.
 #if defined(XP_WIN) && !defined(JS_STANDALONE)
+#  include "mozmemory_utils.h"
 #  include "mozilla/ProcessType.h"
 #endif
 
@@ -1474,60 +1474,6 @@ static inline void ApplyZeroOrJunk(void* aPtr, size_t aSize) {
 // On Windows, delay crashing on OOM.
 #ifdef XP_WIN
 
-namespace mozilla {
-
-namespace detail {
-// Helper for StallAndRetry error messages.
-template <typename T>
-constexpr bool is_std_optional = false;
-template <typename T>
-constexpr bool is_std_optional<std::optional<T>> = true;
-}  // namespace detail
-
-struct StallSpecs {
-  // Maximum number of retry-attempts before giving up.
-  size_t maxAttempts;
-  // Delay time between successive events.
-  size_t delayMs;
-
-  // Retry a fallible operation until it succeeds or until we've run out of
-  // retries.
-  //
-  // Note that this invokes `aDelayFunc` immediately upon being called! It's
-  // intended for use in the unhappy path, after an initial attempt has failed.
-  //
-  // The function type here may be read:
-  // ```
-  // fn StallAndRetry<R>(
-  //     delay_func: impl Fn(usize) -> (),
-  //     operation: impl Fn() -> Option<R>,
-  // ) -> Option<R>;
-  // ```
-  //
-  template <typename DelayFunc, typename OpFunc>
-  auto StallAndRetry(DelayFunc&& aDelayFunc, OpFunc&& aOperation) const
-      -> decltype(aOperation()) {
-    {
-      // Explicit typecheck for OpFunc, to provide an explicit error message.
-      using detail::is_std_optional;
-      static_assert(is_std_optional<decltype(aOperation())>,
-                    "aOperation() must return std::optional");
-
-      // (clang's existing error messages suffice for aDelayFunc.)
-    }
-
-    for (size_t i = 0; i < maxAttempts; ++i) {
-      aDelayFunc(delayMs);
-      if (const auto opt = aOperation()) {
-        return opt;
-      }
-    }
-    return std::nullopt;
-  }
-};
-
-}  // namespace mozilla
-
 // Implementation of VirtualAlloc wrapper (bug 1716727).
 namespace MozAllocRetries {
 

memory/build/mozmemory_utils.h

@@ -0,0 +1,67 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozjemalloc_utils_h
+#define mozjemalloc_utils_h
+
+#include <optional>
+#include <type_traits>
+
+namespace mozilla {
+
+namespace detail {
+// Helper for StallAndRetry error messages.
+template <typename T>
+constexpr bool is_std_optional = false;
+template <typename T>
+constexpr bool is_std_optional<std::optional<T>> = true;
+}  // namespace detail
+
+struct StallSpecs {
+  // Maximum number of retry-attempts before giving up.
+  size_t maxAttempts;
+  // Delay time between successive events.
+  size_t delayMs;
+
+  // Retry a fallible operation until it succeeds or until we've run out of
+  // retries.
+  //
+  // Note that this invokes `aDelayFunc` immediately upon being called! It's
+  // intended for use in the unhappy path, after an initial attempt has failed.
+  //
+  // The function type here may be read:
+  // ```
+  // fn StallAndRetry<R>(
+  //     delay_func: impl Fn(usize) -> (),
+  //     operation: impl Fn() -> Option<R>,
+  // ) -> Option<R>;
+  // ```
+  //
+  template <typename DelayFunc, typename OpFunc>
+  auto StallAndRetry(DelayFunc&& aDelayFunc, OpFunc&& aOperation) const
+      -> decltype(aOperation()) {
+    {
+      // Explicit typecheck for OpFunc, to provide an explicit error message.
+      using detail::is_std_optional;
+      static_assert(is_std_optional<decltype(aOperation())>,
+                    "aOperation() must return std::optional");
+
+      // (clang's existing error messages suffice for aDelayFunc.)
+    }
+
+    for (size_t i = 0; i < maxAttempts; ++i) {
+      aDelayFunc(delayMs);
+      if (const auto opt = aOperation()) {
+        return opt;
+      }
+    }
+    return std::nullopt;
+  }
+};
+
+}  // namespace mozilla
+
+#endif  // mozjemalloc_utils_h

memory/build/test/TestMozJemallocUtils.cpp

@@ -0,0 +1,152 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// This is a cppunittest, rather than a gtest, in order to assert that no
+// additional DLL needs to be linked in to use the function(s) tested herein.
+
+#include <algorithm>
+#include <iostream>
+#include <optional>
+#include <sstream>
+#include <type_traits>
+
+#include "mozmemory_utils.h"
+#include "mozilla/Likely.h"
+
+static bool TESTS_FAILED = false;
+
+// Introduce iostream output operators for std::optional, for convenience's
+// sake.
+//
+// (This is technically undefined behavior per [namespace.std], but it's
+// unlikely to have any surprising effects when confined to this compilation
+// unit.)
+namespace std {
+template <typename T>
+std::ostream& operator<<(std::ostream& o, std::optional<T> const& s) {
+  if (s) {
+    return o << "std::optional{" << s.value() << "}";
+  }
+  return o << "std::nullopt";
+}
+std::ostream& operator<<(std::ostream& o, std::nullopt_t const& s) {
+  return o << "std::nullopt";
+}
+}  // namespace std
+
+// EXPECT_EQ
+//
+// Assert that two expressions are equal. Print them, and their values, on
+// failure. (Based on the GTest macro of the same name.)
+template <typename X, typename Y, size_t Xn, size_t Yn>
+void AssertEqualImpl_(X&& x, Y&& y, const char* file, size_t line,
+                      const char (&xStr)[Xn], const char (&yStr)[Yn],
+                      const char* explanation = nullptr) {
+  if (MOZ_LIKELY(x == y)) return;
+
+  TESTS_FAILED = true;
+
+  std::stringstream sstr;
+  sstr << file << ':' << line << ": ";
+  if (explanation) sstr << explanation << "\n\t";
+  sstr << "expected " << xStr << " (" << x << ") == " << yStr << " (" << y
+       << ")\n";
+  std::cerr << sstr.str() << std::flush;
+}
+
+#define EXPECT_EQ(x, y)                                 \
+  do {                                                  \
+    AssertEqualImpl_(x, y, __FILE__, __LINE__, #x, #y); \
+  } while (0)
+
+// STATIC_ASSERT_VALUE_IS_OF_TYPE
+//
+// Assert that a value `v` is of type `t` (ignoring cv-qualification).
+#define STATIC_ASSERT_VALUE_IS_OF_TYPE(v, t) \
+  static_assert(std::is_same_v<std::remove_cv_t<decltype(v)>, t>)
+
+// MockSleep
+//
+// Mock replacement for ::Sleep that merely logs its calls.
+struct MockSleep {
+  size_t calls = 0;
+  size_t sum = 0;
+
+  void operator()(size_t val) {
+    ++calls;
+    sum += val;
+  }
+
+  bool operator==(MockSleep const& that) const {
+    return calls == that.calls && sum == that.sum;
+  }
+};
+std::ostream& operator<<(std::ostream& o, MockSleep const& s) {
+  return o << "MockSleep { count: " << s.calls << ", sum: " << s.sum << " }";
+}
+
+// MockAlloc
+//
+// Mock memory allocation mechanism. Eventually returns a value.
+template <typename T>
+struct MockAlloc {
+  size_t count;
+  T value;
+
+  std::optional<T> operator()() {
+    if (!count--) return value;
+    return std::nullopt;
+  }
+};
+
+int main() {
+  using mozilla::StallSpecs;
+
+  const StallSpecs stall = {.maxAttempts = 10, .delayMs = 50};
+
+  // semantic test: stalls as requested but still yields a value,
+  // up until it doesn't
+  for (size_t i = 0; i < 20; ++i) {
+    MockSleep sleep;
+    auto const ret =
+        stall.StallAndRetry(sleep, MockAlloc<int>{.count = i, .value = 5});
+    STATIC_ASSERT_VALUE_IS_OF_TYPE(ret, std::optional<int>);
+
+    if (i < 10) {
+      EXPECT_EQ(ret, std::optional<int>(5));
+    } else {
+      EXPECT_EQ(ret, std::nullopt);
+    }
+    size_t const expectedCalls = std::min<size_t>(i + 1, 10);
+    EXPECT_EQ(sleep,
+              (MockSleep{.calls = expectedCalls, .sum = 50 * expectedCalls}));
+  }
+
+  // syntactic test: inline capturing lambda is accepted for aOperation
+  {
+    MockSleep sleep;
+    std::optional<int> value{42};
+    auto const ret = stall.StallAndRetry(sleep, [&]() { return value; });
+
+    STATIC_ASSERT_VALUE_IS_OF_TYPE(ret, std::optional<int>);
+    EXPECT_EQ(ret, std::optional(42));
+    EXPECT_EQ(sleep, (MockSleep{.calls = 1, .sum = 50}));
+  }
+
+  // syntactic test: inline capturing lambda is accepted for aDelayFunc
+  {
+    MockSleep sleep;
+    auto const ret =
+        stall.StallAndRetry([&](size_t time) { sleep(time); },
+                            MockAlloc<int>{.count = 0, .value = 105});
+
+    STATIC_ASSERT_VALUE_IS_OF_TYPE(ret, std::optional<int>);
+    EXPECT_EQ(ret, std::optional(105));
+    EXPECT_EQ(sleep, (MockSleep{.calls = 1, .sum = 50}));
+  }
+
+  return TESTS_FAILED ? 1 : 0;
+}

memory/build/test/moz.build

@@ -0,0 +1,17 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# We don't link these tests against mozglue, but we do use the STL. Avoid the
+# implicit linking of `__imp_moz_xalloc` in our STL wrappers.
+DisableStlWrapping()
+
+# Important: for these tests to be run, they also need to be added
+# to testing/cppunittest.ini.
+CppUnitTests(
+    [
+        "TestMozJemallocUtils",
+    ]
+)

testing/cppunittest.ini

@@ -48,6 +48,7 @@ skip-if = os != 'win'
 skip-if = os != 'linux'
 [TestMMPolicy]
 skip-if = os != 'win'
+[TestMozJemallocUtils]
 [TestNativeNt]
 skip-if = os != 'win'
 [TestUriValidation]