Bug 1795311 - A new shared memory class with more flexible memory management. r=nika,jld

Differential Revision: https://phabricator.services.mozilla.com/D159398

ipc/glue/RawShmem.cpp

@@ -0,0 +1,114 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#include "RawShmem.h"
+#include "mozilla/ipc/ProtocolUtils.h"
+
+namespace mozilla::ipc {
+
+UnsafeSharedMemoryHandle::UnsafeSharedMemoryHandle()
+    : mHandle(ipc::SharedMemoryBasic::NULLHandle()), mSize(0) {}
+
+UnsafeSharedMemoryHandle::UnsafeSharedMemoryHandle(
+    UnsafeSharedMemoryHandle&& aOther) noexcept
+    : mHandle(std::move(aOther.mHandle)), mSize(aOther.mSize) {
+  aOther.mHandle = ipc::SharedMemoryBasic::NULLHandle();
+  aOther.mSize = 0;
+}
+
+UnsafeSharedMemoryHandle& UnsafeSharedMemoryHandle::operator=(
+    UnsafeSharedMemoryHandle&& aOther) noexcept {
+  if (this == &aOther) {
+    return *this;
+  }
+
+  mHandle = std::move(aOther.mHandle);
+  mSize = aOther.mSize;
+  aOther.mHandle = ipc::SharedMemoryBasic::NULLHandle();
+  aOther.mSize = 0;
+  return *this;
+}
+
+Maybe<std::pair<UnsafeSharedMemoryHandle, WritableSharedMemoryMapping>>
+UnsafeSharedMemoryHandle::CreateAndMap(size_t aSize) {
+  if (aSize == 0) {
+    return Some(std::make_pair(UnsafeSharedMemoryHandle(),
+                               WritableSharedMemoryMapping()));
+  }
+
+  RefPtr<ipc::SharedMemoryBasic> shm = MakeAndAddRef<ipc::SharedMemoryBasic>();
+  if (NS_WARN_IF(!shm->Create(aSize)) || NS_WARN_IF(!shm->Map(aSize))) {
+    return Nothing();
+  }
+
+  // TODO(bug 1797039): At the moment the handle/mapping distinction is
+  // implemented on top of a single class SharedMemoryBasic. It leads to a few
+  // awkward or sub-optimal things such as how the following few lines clone
+  // then close the handle. It would be better to separate the underlying
+  // implementation or steal the handle to avoid cloning it.
+  auto handle = shm->CloneHandle();
+
+  shm->CloseHandle();
+  auto size = shm->Size();
+
+  return Some(std::make_pair(UnsafeSharedMemoryHandle(std::move(handle), size),
+                             WritableSharedMemoryMapping(std::move(shm))));
+}
+
+WritableSharedMemoryMapping::WritableSharedMemoryMapping(
+    RefPtr<ipc::SharedMemoryBasic>&& aRef)
+    : mRef(aRef) {}
+
+Maybe<WritableSharedMemoryMapping> WritableSharedMemoryMapping::Open(
+    UnsafeSharedMemoryHandle aHandle) {
+  if (aHandle.mSize == 0) {
+    return Some(WritableSharedMemoryMapping(nullptr));
+  }
+
+  RefPtr<ipc::SharedMemoryBasic> shm = MakeAndAddRef<ipc::SharedMemoryBasic>();
+  if (NS_WARN_IF(!shm->SetHandle(std::move(aHandle.mHandle),
+                                 ipc::SharedMemory::RightsReadWrite)) ||
+      NS_WARN_IF(!shm->Map(aHandle.mSize))) {
+    return Nothing();
+  }
+
+  shm->CloseHandle();
+
+  return Some(WritableSharedMemoryMapping(std::move(shm)));
+}
+
+size_t WritableSharedMemoryMapping::Size() const {
+  if (!mRef) {
+    return 0;
+  }
+
+  return mRef->Size();
+}
+
+Span<uint8_t> WritableSharedMemoryMapping::Bytes() {
+  if (!mRef) {
+    return Span<uint8_t>();
+  }
+
+  uint8_t* mem = static_cast<uint8_t*>(mRef->memory());
+  return Span(mem, mRef->Size());
+}
+
+}  // namespace mozilla::ipc
+
+namespace IPC {
+auto ParamTraits<mozilla::ipc::UnsafeSharedMemoryHandle>::Write(
+    IPC::MessageWriter* aWriter, paramType&& aVar) -> void {
+  IPC::WriteParam(aWriter, std::move(aVar.mHandle));
+  IPC::WriteParam(aWriter, aVar.mSize);
+}
+
+auto ParamTraits<mozilla::ipc::UnsafeSharedMemoryHandle>::Read(
+    IPC::MessageReader* aReader, paramType* aVar) -> bool {
+  return IPC::ReadParam(aReader, &aVar->mHandle) &&
+         IPC::ReadParam(aReader, &aVar->mSize);
+}
+
+}  // namespace IPC

ipc/glue/RawShmem.h

@@ -0,0 +1,113 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 MOZILLA_IPC_RAWSHMEM_H_
+#define MOZILLA_IPC_RAWSHMEM_H_
+
+#include "mozilla/ipc/SharedMemoryBasic.h"
+#include "mozilla/Span.h"
+#include <utility>
+
+namespace mozilla::ipc {
+
+class WritableSharedMemoryMapping;
+
+/// A handle to shared memory.
+///
+/// See the doc comment for `WritableSharedMemoryMapping` below.
+class UnsafeSharedMemoryHandle {
+  friend class WritableSharedMemoryMapping;
+  friend struct IPC::ParamTraits<UnsafeSharedMemoryHandle>;
+
+ public:
+  UnsafeSharedMemoryHandle();
+  UnsafeSharedMemoryHandle(UnsafeSharedMemoryHandle&& aOther) noexcept;
+  UnsafeSharedMemoryHandle& operator=(
+      UnsafeSharedMemoryHandle&& aOther) noexcept;
+
+  /// Attempts to allocate a shmem.
+  ///
+  /// Returns `Nothing()` if allocation fails.
+  /// If `aSize` is zero, a valid empty WritableSharedMemoryMapping is returned.
+  static Maybe<std::pair<UnsafeSharedMemoryHandle, WritableSharedMemoryMapping>>
+  CreateAndMap(size_t aSize);
+
+ private:
+  UnsafeSharedMemoryHandle(SharedMemoryBasic::Handle&& aHandle, uint64_t aSize)
+      : mHandle(std::move(aHandle)), mSize(aSize) {}
+
+  SharedMemoryBasic::Handle mHandle;
+  uint64_t mSize;
+};
+
+/// A Shared memory buffer mapping.
+///
+/// Unlike `ipc::Shmem`, the underlying shared memory buffer on each side of
+/// the process boundary is only deallocated with there respective
+/// `WritableSharedMemoryMapping`.
+///
+/// ## Usage
+///
+/// Typical usage goes as follows:
+/// - Allocate the memory using `UnsafeSharedMemoryHandle::Create`, returning a
+///   handle and a mapping.
+/// - Send the handle to the other process using an IPDL message.
+/// - On the other process, map the shared memory by creating
+///   WritableSharedMemoryMapping via `WritableSharedMemoryMapping::Open` and
+///   the received handle.
+///
+/// Do not send the shared memory handle again, it is only intended to establish
+/// the mapping on each side during initialization. The user of this class is
+/// responsible for managing the lifetime of the buffers on each side, as well
+/// as their identity, by for example storing them in hash map and referring to
+/// them via IDs in IPDL message if need be.
+///
+/// ## Empty shmems
+///
+/// An empty WritableSharedMemoryMapping is one that was created with size zero.
+/// It is analogous to a null RefPtr. It can be used like a non-empty shmem,
+/// including sending the handle and openning it on another process (resulting
+/// in an empty mapping on the other side).
+class WritableSharedMemoryMapping {
+  friend class UnsafeSharedMemoryHandle;
+
+ public:
+  WritableSharedMemoryMapping() = default;
+
+  WritableSharedMemoryMapping(WritableSharedMemoryMapping&& aMoved) =
+      default;
+
+  WritableSharedMemoryMapping& operator=(WritableSharedMemoryMapping&& aMoved) =
+      default;
+
+  /// Open the shmem and immediately close the handle.
+  static Maybe<WritableSharedMemoryMapping> Open(
+      UnsafeSharedMemoryHandle aHandle);
+
+  // Returns the size in bytes.
+  size_t Size() const;
+
+  // Returns the shared memory as byte range.
+  Span<uint8_t> Bytes();
+
+ private:
+  explicit WritableSharedMemoryMapping(RefPtr<ipc::SharedMemoryBasic>&& aRef);
+
+  RefPtr<ipc::SharedMemoryBasic> mRef;
+};
+
+}  // namespace mozilla::ipc
+
+namespace IPC {
+template <>
+struct ParamTraits<mozilla::ipc::UnsafeSharedMemoryHandle> {
+  typedef mozilla::ipc::UnsafeSharedMemoryHandle paramType;
+  static void Write(IPC::MessageWriter* aWriter, paramType&& aVar);
+  static bool Read(IPC::MessageReader* aReader, paramType* aVar);
+};
+
+}  // namespace IPC
+
+#endif

ipc/glue/moz.build

@@ -52,6 +52,7 @@ EXPORTS.mozilla.ipc += [
     "ProtocolUtils.h",
     "ProtocolUtilsFwd.h",
     "RandomAccessStreamUtils.h",
+    "RawShmem.h",
     "ScopedPort.h",
     "ScopedXREEmbed.h",
     "SerializedStructuredCloneBuffer.h",
@@ -180,6 +181,7 @@ UNIFIED_SOURCES += [
     "ProcessUtils_common.cpp",
     "ProtocolUtils.cpp",
     "RandomAccessStreamUtils.cpp",
+    "RawShmem.cpp",
     "ScopedPort.cpp",
     "ScopedXREEmbed.cpp",
     "SerializedStructuredCloneBuffer.cpp",

ipc/gtest/TestUnsafeSharedMemoryHandle.cpp

@@ -0,0 +1,58 @@
+/* -*- 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/. */
+
+#include "chrome/common/ipc_message.h"
+#include "chrome/common/ipc_message_utils.h"
+#include "gtest/gtest.h"
+
+#include "mozilla/RandomNum.h"
+#include "mozilla/ipc/RawShmem.h"
+
+namespace mozilla::ipc {
+
+static bool SerializeAndDeserialize(UnsafeSharedMemoryHandle&& aIn,
+                                    UnsafeSharedMemoryHandle* aOut) {
+  IPC::Message msg(MSG_ROUTING_NONE, 0);
+  {
+    IPC::MessageWriter writer(msg);
+    IPC::WriteParam(&writer, std::move(aIn));
+  }
+
+  IPC::MessageReader reader(msg);
+  return IPC::ReadParam(&reader, aOut);
+}
+
+void TestUnsafeSharedMemoryHandle(size_t aSize) {
+  auto maybeHandle = UnsafeSharedMemoryHandle::CreateAndMap(aSize);
+  ASSERT_TRUE(maybeHandle);
+  auto [handle, mapping] = maybeHandle.extract();
+
+  EXPECT_EQ(mapping.Size(), aSize);
+
+  auto inBytes = mapping.Bytes();
+  for (size_t i = 0; i < aSize; ++i) {
+    inBytes[i] = static_cast<uint8_t>(i % 255);
+  }
+
+  UnsafeSharedMemoryHandle out;
+  ASSERT_TRUE(SerializeAndDeserialize(std::move(handle), &out));
+
+  auto mapping2 = WritableSharedMemoryMapping::Open(std::move(out)).value();
+
+  EXPECT_EQ(mapping2.Size(), aSize);
+  auto outBytes = mapping2.Bytes();
+  for (size_t i = 0; i < aSize; ++i) {
+    EXPECT_EQ(outBytes[i], static_cast<uint8_t>(i % 255));
+  }
+}
+
+TEST(UnsafeSharedMemoryHandle, Empty)
+{ TestUnsafeSharedMemoryHandle(0); }
+
+TEST(UnsafeSharedMemoryHandle, SmallSize)
+{ TestUnsafeSharedMemoryHandle(2048); }
+
+}  // namespace mozilla::ipc

ipc/gtest/moz.build

@@ -12,6 +12,7 @@ SOURCES += [
     "TestLogging.cpp",
     "TestRandomAccessStreamUtils.cpp",
     "TestSharedMemory.cpp",
+    "TestUnsafeSharedMemoryHandle.cpp",
 ]
 
 include("/ipc/chromium/chromium-config.mozbuild")