[mojo] Implement data pipe using a shared buffer.

mojo/edk/system/data_pipe.cc

Index: mojo/edk/system/data_pipe.cc
diff --git a/mojo/edk/system/data_pipe.cc b/mojo/edk/system/data_pipe.cc
index 54a6df45ae6bb2d434b1d28d2b314ac2cd2c8703..9371b25de78e701487851fa98b0a5af831f77b11 100644
--- a/mojo/edk/system/data_pipe.cc
+++ b/mojo/edk/system/data_pipe.cc
@@ -11,6 +11,11 @@
 #include <algorithm>
 #include <limits>
 
+#include "base/bind.h"
+#include "mojo/edk/embedder/embedder_internal.h"
+#include "mojo/edk/embedder/platform_support.h"
+#include "mojo/edk/system/broker.h"
+
 #include "mojo/edk/system/configuration.h"
 #include "mojo/edk/system/options_validation.h"
 #include "mojo/edk/system/raw_channel.h"
@@ -24,15 +29,20 @@ namespace {
 const uint32_t kInvalidDataPipeHandleIndex = static_cast<uint32_t>(-1);
 
 struct MOJO_ALIGNAS(8) SerializedDataPipeHandleDispatcher {
-  uint32_t platform_handle_index;  // (Or |kInvalidDataPipeHandleIndex|.)
+  uint32_t channel_handle_index;  // (Or |kInvalidDataPipeHandleIndex|.)
 
   // These are from MojoCreateDataPipeOptions
   MojoCreateDataPipeOptionsFlags flags;
   uint32_t element_num_bytes;
   uint32_t capacity_num_bytes;
 
-  uint32_t shared_memory_handle_index;  // (Or |kInvalidDataPipeHandleIndex|.)
-  uint32_t shared_memory_size;
+  uint32_t channel_shared_handle_index;  // (Or |kInvalidDataPipeHandleIndex|.)
+  uint32_t channel_pending_read_size;
+  uint32_t channel_pending_write_size;
+
+  uint32_t shared_buffer_handle_index;
+  uint32_t ring_buffer_start;
+  uint32_t ring_buffer_size;
 };
 
 }  // namespace
@@ -100,50 +110,175 @@ MojoResult DataPipe::ValidateCreateOptions(
   return MOJO_RESULT_OK;
 }
 
-void DataPipe::StartSerialize(bool have_channel_handle,
-                              bool have_shared_memory,
-                              size_t* max_size,
-                              size_t* max_platform_handles) {
+DataPipe::DataPipe(const MojoCreateDataPipeOptions& options)
+    : channel_(nullptr),
+      options_(options),
+      channel_released_(false),
+      shared_buffer_(nullptr),
+      mapping_(nullptr),
+      ring_buffer_start_(0u),
+      ring_buffer_size_(0u) {}
+
+DataPipe::~DataPipe() {}
+
+void DataPipe::Init(ScopedPlatformHandle message_pipe,

[Anand Mistry (off Chromium), 2016/01/11 06:19:34]

s/message_pipe/channel
where appropriate.

[Eliot Courtney, 2016/01/13 00:00:09]

Done.

+                    char* serialized_write_buffer,
+                    uint32_t serialized_write_buffer_size,
+                    char* serialized_read_buffer,
+                    uint32_t serialized_read_buffer_size,
+                    ScopedPlatformHandle shared_buffer_handle,
+                    uint32_t ring_buffer_start,
+                    uint32_t ring_buffer_size,
+                    bool is_producer,
+                    const base::Closure& init_callback) {
+  is_producer_ = is_producer;
+
+  ring_buffer_start_ = ring_buffer_start;
+  ring_buffer_size_ = ring_buffer_size;
+
+  if (shared_buffer_handle.is_valid()) {
+    shared_buffer_ = internal::g_platform_support->CreateSharedBufferFromHandle(
+        options_.capacity_num_bytes, std::move(shared_buffer_handle));
+    DCHECK(shared_buffer_);
+  } else if (is_producer_) {
+#if defined(OS_WIN)
+    shared_buffer_ = internal::g_platform_support->CreateSharedBuffer(
+        options_.capacity_num_bytes);
+#else
+    shared_buffer_ =
+        internal::g_broker->CreateSharedBuffer(options_.capacity_num_bytes);
+#endif
+    CHECK(shared_buffer_);
+  }
+
+  if (message_pipe.is_valid()) {
+    channel_ = RawChannel::Create(std::move(message_pipe));
+    channel_->SetSerializedData(serialized_read_buffer,
+                                serialized_read_buffer_size,
+                                serialized_write_buffer,
+                                serialized_write_buffer_size, nullptr, nullptr);
+    internal::g_io_thread_task_runner->PostTask(FROM_HERE, init_callback);
+    channel_->EnsureLazyInitialized();
+
+    if (is_producer_) {
+      internal::g_io_thread_task_runner->PostTask(
+          FROM_HERE, base::Bind(&DataPipe::NotifySharedBuffer, this));
+    }
+  }
+}
+
+void DataPipe::StartSerialize(size_t* max_size, size_t* max_platform_handles) {
+  // We need to release the channel and get its pending reads/writes.
+  if (!channel_released_) {
+    Serialize();
+  }
+
   *max_size = sizeof(SerializedDataPipeHandleDispatcher);
   *max_platform_handles = 0;
-  if (have_channel_handle)
+  if (serialized_channel_handle_.is_valid())
     (*max_platform_handles)++;
-  if (have_shared_memory)
+  // For shared buffer to transfer pending reads / writes.
+  if (!serialized_write_buffer_.empty() || !serialized_read_buffer_.empty())
     (*max_platform_handles)++;
+  if (shared_buffer_)
+    (*max_platform_handles)++;
+}
+
+void DataPipe::Serialize() {
+  // We need to stop watching handle immediately, even though not on IO thread,
+  // so that other messages aren't read after this.
+  if (channel_) {
+    std::vector<int> fds;
+    bool write_error = false;
+    serialized_channel_handle_ = channel_->ReleaseHandle(

[Anand Mistry (off Chromium), 2016/01/11 06:19:34]

From what I can tell, this is racy. Basically, this ends up deleting the
read/write MessageLoopForIO::FileDescriptorWatcher's (on posix) from a non-IO
thread. Based on my reading of libevent/message_pump_libevent, this is incorrect
and racy behaviour.

[Eliot Courtney, 2016/01/14 02:17:57]

Discussed offline -- this is fairly impossible to fix with the EDK design, and
also no more racy than what previously existed.

+        &serialized_read_buffer_, &serialized_write_buffer_, &fds, &fds,
+        &write_error);
+
+    CHECK(fds.empty());
+    if (write_error) {
+      serialized_channel_handle_.reset();
+    }
+    channel_ = nullptr;
+  }
+  channel_released_ = true;
 }
 
-void DataPipe::EndSerialize(const MojoCreateDataPipeOptions& options,
-                            ScopedPlatformHandle channel_handle,
-                            ScopedPlatformHandle shared_memory_handle,
-                            size_t shared_memory_size,
-                            void* destination,
+void DataPipe::EndSerialize(void* destination,
                             size_t* actual_size,
                             PlatformHandleVector* platform_handles) {
+  ScopedPlatformHandle channel_shared_handle;
+  size_t channel_shared_size =
+      serialized_read_buffer_.size() + serialized_write_buffer_.size();
+  if (channel_shared_size) {
+#if defined(OS_WIN)
+    scoped_refptr<PlatformSharedBuffer> shared_buffer(
+        internal::g_platform_support->CreateSharedBuffer(channel_shared_size));
+#else
+    scoped_refptr<PlatformSharedBuffer> shared_buffer(
+        internal::g_broker->CreateSharedBuffer(channel_shared_size));
+#endif
+
+    scoped_ptr<PlatformSharedBufferMapping> mapping(
+        shared_buffer->Map(0, channel_shared_size));
+
+    void* base = mapping->GetBase();
+    if (!serialized_read_buffer_.empty()) {
+      memcpy(base, &serialized_read_buffer_[0], serialized_read_buffer_.size());
+    }
+    if (!serialized_write_buffer_.empty()) {
+      memcpy(static_cast<uint8_t*>(base) + serialized_read_buffer_.size(),
+             &serialized_write_buffer_[0], serialized_write_buffer_.size());
+    }
+
+    channel_shared_handle.reset(shared_buffer->PassPlatformHandle().release());
+  }
+
   SerializedDataPipeHandleDispatcher* serialization =
       static_cast<SerializedDataPipeHandleDispatcher*>(destination);
-  if (channel_handle.is_valid()) {
+  if (serialized_channel_handle_.is_valid()) {
     DCHECK(platform_handles->size() < std::numeric_limits<uint32_t>::max());
-    serialization->platform_handle_index =
+    serialization->channel_handle_index =
         static_cast<uint32_t>(platform_handles->size());
-    platform_handles->push_back(channel_handle.release());
+    platform_handles->push_back(serialized_channel_handle_.release());
   } else {
-    serialization->platform_handle_index = kInvalidDataPipeHandleIndex;
+    serialization->channel_handle_index = kInvalidDataPipeHandleIndex;
   }
 
-  serialization->flags = options.flags;
-  serialization->element_num_bytes = options.element_num_bytes;
-  serialization->capacity_num_bytes = options.capacity_num_bytes;
+  serialization->flags = options_.flags;
+  serialization->element_num_bytes = options_.element_num_bytes;
+  serialization->capacity_num_bytes = options_.capacity_num_bytes;
 
-  serialization->shared_memory_size = static_cast<uint32_t>(shared_memory_size);
-  if (serialization->shared_memory_size) {
+  serialization->channel_pending_read_size =
+      static_cast<uint32_t>(serialized_read_buffer_.size());
+  serialization->channel_pending_write_size =
+      static_cast<uint32_t>(serialized_write_buffer_.size());
+
+  if (channel_shared_handle.is_valid()) {
     DCHECK(platform_handles->size() < std::numeric_limits<uint32_t>::max());
-    serialization->shared_memory_handle_index =
+    serialization->channel_shared_handle_index =
         static_cast<uint32_t>(platform_handles->size());
-    platform_handles->push_back(shared_memory_handle.release());
+    platform_handles->push_back(channel_shared_handle.release());
   } else {
-    serialization->shared_memory_handle_index = kInvalidDataPipeHandleIndex;
+    serialization->channel_shared_handle_index = kInvalidDataPipeHandleIndex;
+  }
+
+  ScopedPlatformHandle shared_buffer_handle;
+  if (shared_buffer_) {
+    shared_buffer_handle.reset(shared_buffer_->PassPlatformHandle().release());
   }
 
+  if (shared_buffer_handle.is_valid()) {
+    DCHECK(platform_handles->size() < std::numeric_limits<uint32_t>::max());
+    serialization->shared_buffer_handle_index =
+        static_cast<uint32_t>(platform_handles->size());
+    platform_handles->push_back(shared_buffer_handle.release());
+  } else {
+    serialization->shared_buffer_handle_index = kInvalidDataPipeHandleIndex;
+  }
+
+  serialization->ring_buffer_start = ring_buffer_start_;
+  serialization->ring_buffer_size = ring_buffer_size_;
+
   *actual_size = sizeof(SerializedDataPipeHandleDispatcher);
 }
 
@@ -152,8 +287,12 @@ ScopedPlatformHandle DataPipe::Deserialize(
     size_t size,
     PlatformHandleVector* platform_handles,
     MojoCreateDataPipeOptions* options,
-    ScopedPlatformHandle* shared_memory_handle,
-    size_t* shared_memory_size) {
+    ScopedPlatformHandle* channel_shared_handle,
+    uint32_t* serialized_read_buffer_size,
+    uint32_t* serialized_write_buffer_size,
+    ScopedPlatformHandle* shared_buffer_handle,
+    uint32_t* ring_buffer_start,
+    uint32_t* ring_buffer_size) {
   if (size != sizeof(SerializedDataPipeHandleDispatcher)) {
     LOG(ERROR) << "Invalid serialized data pipe dispatcher (bad size)";
     return ScopedPlatformHandle();
@@ -161,52 +300,308 @@ ScopedPlatformHandle DataPipe::Deserialize(
 
   const SerializedDataPipeHandleDispatcher* serialization =
       static_cast<const SerializedDataPipeHandleDispatcher*>(source);
-  size_t platform_handle_index = serialization->platform_handle_index;
 
   // Starts off invalid, which is what we want.
-  PlatformHandle platform_handle;
-  if (platform_handle_index != kInvalidDataPipeHandleIndex) {
-    if (!platform_handles ||
-        platform_handle_index >= platform_handles->size()) {
-      LOG(ERROR)
-          << "Invalid serialized data pipe dispatcher (missing handles)";
+  PlatformHandle channel_handle;
+  uint32_t channel_handle_index = serialization->channel_handle_index;
+  if (channel_handle_index != kInvalidDataPipeHandleIndex) {
+    if (!platform_handles || channel_handle_index >= platform_handles->size()) {
+      LOG(ERROR) << "Invalid serialized data pipe dispatcher (missing handles)";
       return ScopedPlatformHandle();
     }
 
     // We take ownership of the handle, so we have to invalidate the one in
     // |platform_handles|.
-    std::swap(platform_handle, (*platform_handles)[platform_handle_index]);
+    std::swap(channel_handle, (*platform_handles)[channel_handle_index]);
   }
 
   options->struct_size = sizeof(MojoCreateDataPipeOptions);
   options->flags = serialization->flags;
   options->element_num_bytes = serialization->element_num_bytes;
   options->capacity_num_bytes = serialization->capacity_num_bytes;
+  *serialized_read_buffer_size = serialization->channel_pending_read_size;
+  *serialized_write_buffer_size = serialization->channel_pending_write_size;
+  *ring_buffer_start = serialization->ring_buffer_start;
+  *ring_buffer_size = serialization->ring_buffer_size;
+
+  uint32_t channel_shared_handle_index =
+      serialization->channel_shared_handle_index;
+  if (*serialized_read_buffer_size || *serialized_write_buffer_size) {
+    DCHECK_NE(channel_shared_handle_index, kInvalidDataPipeHandleIndex);
+    if (!platform_handles ||
+        channel_shared_handle_index >= platform_handles->size()) {
+      LOG(ERROR) << "Invalid serialized data pipe dispatcher (missing handles)";
+      return ScopedPlatformHandle();
+    }
 
-  if (shared_memory_size) {
-    *shared_memory_size = serialization->shared_memory_size;
-    if (*shared_memory_size) {
-      DCHECK(serialization->shared_memory_handle_index !=
-             kInvalidDataPipeHandleIndex);
-      if (!platform_handles ||
-          serialization->shared_memory_handle_index >=
-              platform_handles->size()) {
-        LOG(ERROR) << "Invalid serialized data pipe dispatcher "
-                   << "(missing handles)";
-        return ScopedPlatformHandle();
-      }
+    // Take ownership.
+    PlatformHandle temp_channel_shared_handle;
+    std::swap(temp_channel_shared_handle,
+              (*platform_handles)[channel_shared_handle_index]);
+    *channel_shared_handle = ScopedPlatformHandle(temp_channel_shared_handle);
+  }
 
-      PlatformHandle temp_shared_memory_handle;
-      std::swap(temp_shared_memory_handle,
-                (*platform_handles)[serialization->shared_memory_handle_index]);
-      *shared_memory_handle =
-          ScopedPlatformHandle(temp_shared_memory_handle);
+  uint32_t shared_buffer_handle_index =
+      serialization->shared_buffer_handle_index;
+  if (shared_buffer_handle_index != kInvalidDataPipeHandleIndex) {
+    if (!platform_handles ||
+        shared_buffer_handle_index >= platform_handles->size()) {
+      LOG(ERROR) << "Invalid serialized data pipe dispatcher (missing handles)";
+      return ScopedPlatformHandle();
     }
+
+    // Take ownership.
+    PlatformHandle temp_shared_buffer_handle;
+    std::swap(temp_shared_buffer_handle,
+              (*platform_handles)[shared_buffer_handle_index]);
+    *shared_buffer_handle = ScopedPlatformHandle(temp_shared_buffer_handle);
   }
 
-  size -= sizeof(SerializedDataPipeHandleDispatcher);
+  return ScopedPlatformHandle(channel_handle);
+}
+
+uint8_t* DataPipe::GetSharedBufferBase() {
+  if (!mapping_) {
+    DCHECK(shared_buffer_);
+    mapping_ = shared_buffer_->Map(0, options_.capacity_num_bytes);
+  }
+  if (!mapping_)
+    return nullptr;
+  return static_cast<uint8_t*>(mapping_->GetBase());
+}
+
+bool DataPipe::WriteDataIntoSharedBuffer(const void* elements,
+                                         uint32_t num_bytes) {
+  uint32_t buffer_size = options_.capacity_num_bytes;
+  uint8_t* base = GetSharedBufferBase();
+  if (!base)
+    return false;
+
+  DCHECK_EQ(num_bytes % options_.element_num_bytes, 0u);
+  DCHECK_LE(num_bytes, buffer_size - ring_buffer_size_);
+
+  uint32_t ring_buffer_end =
+      (ring_buffer_start_ + ring_buffer_size_) % buffer_size;
+  if (ring_buffer_size_ == 0 || ring_buffer_start_ < ring_buffer_end) {
+    uint32_t bytes_until_end = buffer_size - ring_buffer_end;
+    memcpy(base + ring_buffer_end, elements,
+           std::min(num_bytes, bytes_until_end));
+
+    if (bytes_until_end < num_bytes) {
+      memcpy(base, static_cast<const uint8_t*>(elements) + bytes_until_end,
+             num_bytes - bytes_until_end);
+    }
+  } else {
+    memcpy(base + ring_buffer_end, elements, num_bytes);
+  }
+
+  return true;
+}
+
+bool DataPipe::ReadDataFromSharedBuffer(void* data, uint32_t num_bytes) {
+  DCHECK_LE(num_bytes, ring_buffer_size_);
+  DCHECK_EQ(num_bytes % options_.element_num_bytes, 0u);
+
+  uint32_t buffer_size = options_.capacity_num_bytes;
+  uint8_t* base = GetSharedBufferBase();
+  if (!base)
+    return false;
+
+  uint32_t ring_buffer_end =
+      (ring_buffer_start_ + ring_buffer_size_) % buffer_size;
+  if (ring_buffer_size_ == 0 || ring_buffer_start_ < ring_buffer_end) {
+    memcpy(data, base + ring_buffer_start_, num_bytes);
+  } else {
+    uint32_t bytes_until_end = buffer_size - ring_buffer_start_;
+    memcpy(data, base + ring_buffer_start_,
+           std::min(num_bytes, bytes_until_end));
+
+    if (bytes_until_end < num_bytes) {
+      memcpy(static_cast<uint8_t*>(data) + bytes_until_end, base,
+             num_bytes - bytes_until_end);
+    }
+  }
+
+  return true;
+}
+
+uint32_t DataPipe::GetReadableBytes() const {
+  return shared_buffer_ ? ring_buffer_size_ : 0;
+}
+
+uint32_t DataPipe::GetWritableBytes() const {
+  return shared_buffer_ ? options_.capacity_num_bytes - ring_buffer_size_ : 0;
+}
+
+void DataPipe::UpdateFromRead(uint32_t num_bytes) {
+  ring_buffer_start_ =
+      (ring_buffer_start_ + num_bytes) % options_.capacity_num_bytes;
+  ring_buffer_size_ -= num_bytes;
+  DCHECK_GE(ring_buffer_size_, 0u);
+}
+
+void DataPipe::UpdateFromWrite(uint32_t num_bytes) {
+  ring_buffer_size_ += num_bytes;
+  DCHECK_LE(ring_buffer_size_, options_.capacity_num_bytes);
+}
+
+bool DataPipe::NotifyWrite(uint32_t num_bytes) {
+  DCHECK(is_producer_);
+
+  if (!channel_)
+    return false;
+
+  DataPipeCommandHeader command = {DATA_WRITTEN, num_bytes};
+  scoped_ptr<MessageInTransit> message(new MessageInTransit(
+      MessageInTransit::Type::MESSAGE, sizeof(command), &command));
+  if (!channel_->WriteMessage(std::move(message))) {
+    return false;
+  }
+  return true;
+}
+
+bool DataPipe::NotifyRead(uint32_t num_bytes) {
+  DCHECK(!is_producer_);
+
+  if (!channel_)
+    return false;
+  DataPipeCommandHeader command = {DATA_READ, num_bytes};
+  scoped_ptr<MessageInTransit> message(new MessageInTransit(
+      MessageInTransit::Type::MESSAGE, sizeof(command), &command));
+  if (!channel_->WriteMessage(std::move(message))) {
+    return false;
+  }
+  return true;
+}
+
+void DataPipe::NotifySharedBuffer() {
+  if (!channel_) {
+    DLOG(ERROR) << "NotifySharedBuffer: No channel";
+    return;
+  }
+  DataPipeCommandHeader command = {NOTIFY_SHARED_BUFFER,
+                                   options_.capacity_num_bytes};
+  ScopedPlatformHandle handle = shared_buffer_->DuplicatePlatformHandle();
+  DCHECK(handle.is_valid());
+  ScopedPlatformHandleVectorPtr fds(new PlatformHandleVector());
+  fds->push_back(handle.release());
+
+  scoped_ptr<MessageInTransit> message(new MessageInTransit(
+      MessageInTransit::Type::MESSAGE, sizeof(command), &command));
+  message->SetTransportData(make_scoped_ptr(new TransportData(
+      std::move(fds), channel_->GetSerializedPlatformHandleSize())));
+  if (!channel_->WriteMessage(std::move(message))) {
+    DLOG(ERROR) << "NotifySharedBuffer: Can't write";
+  }
+}
+
+void DataPipe::UpdateSharedBuffer(
+    scoped_refptr<PlatformSharedBuffer> shared_buffer) {
+  DCHECK(shared_buffer);
+  shared_buffer_ = shared_buffer;
+  mapping_ = nullptr;
+}
+
+void DataPipe::Shutdown() {
+  if (channel_) {
+    channel_->Shutdown();
+    channel_ = nullptr;
+  }
+}
+
+void DataPipe::CreateEquivalentAndClose(DataPipe* out) {
+  // Serialize, releasing the handle, otherwise we will get callbacks to the
+  // wrong delegate for RawChannel.
+  Serialize();
+
+  std::swap(options_, out->options_);
+  std::swap(channel_released_, out->channel_released_);
+  serialized_read_buffer_.swap(out->serialized_read_buffer_);
+  serialized_write_buffer_.swap(out->serialized_write_buffer_);
+  serialized_channel_handle_.swap(out->serialized_channel_handle_);
+  shared_buffer_.swap(out->shared_buffer_);
+  mapping_.swap(out->mapping_);
+  std::swap(ring_buffer_start_, out->ring_buffer_start_);
+  std::swap(ring_buffer_size_, out->ring_buffer_size_);
+  std::swap(is_producer_, out->is_producer_);
+}
+
+void* DataPipe::GetWriteBuffer(uint32_t* num_bytes) {
+  if (!shared_buffer_) {
+    *num_bytes = 0;
+    return nullptr;
+  }
+  // Must provide sequential memory.
+  uint32_t buffer_size = options_.capacity_num_bytes;
+  uint32_t ring_buffer_end =
+      (ring_buffer_start_ + ring_buffer_size_) % buffer_size;
+  if (ring_buffer_size_ == 0 || ring_buffer_start_ < ring_buffer_end) {
+    *num_bytes = buffer_size - ring_buffer_end;
+  } else {
+    *num_bytes = ring_buffer_start_ - ring_buffer_end;
+  }
+
+  return GetSharedBufferBase() + ring_buffer_end;
+}
+
+const void* DataPipe::GetReadBuffer(uint32_t* num_bytes) {
+  if (!shared_buffer_) {
+    *num_bytes = 0;
+    return nullptr;
+  }
+  // Must provide sequential memory.
+  uint32_t buffer_size = options_.capacity_num_bytes;
+  uint32_t ring_buffer_end =
+      (ring_buffer_start_ + ring_buffer_size_) % buffer_size;
+  if (ring_buffer_size_ == 0 || ring_buffer_start_ < ring_buffer_end) {
+    *num_bytes = ring_buffer_size_;
+  } else {
+    *num_bytes = buffer_size - ring_buffer_start_;
+  }
+
+  return GetSharedBufferBase() + ring_buffer_start_;
+}
+
+bool DataPipe::ProcessCommand(const DataPipeCommandHeader& command,
+                              ScopedPlatformHandleVectorPtr platform_handles) {
+  PlatformHandle handle;
+  ScopedPlatformHandle scoped_handle;
+  scoped_refptr<PlatformSharedBuffer> shared_buffer;
+  bool was_unreadable = GetReadableBytes() == 0;
+  bool was_unwritable = GetWritableBytes() == 0;
+  switch (command.command) {
+    case NOTIFY_SHARED_BUFFER:
+      CHECK_EQ(platform_handles->size(), 1u);
+      std::swap(handle, (*platform_handles.get())[0]);
+      scoped_handle.reset(handle);
+      UpdateSharedBuffer(
+          internal::g_platform_support->CreateSharedBufferFromHandle(
+              command.num_bytes, std::move(scoped_handle)));
+      break;
+    case DATA_WRITTEN:
+      if (!is_producer_) {
+        UpdateFromWrite(command.num_bytes);
+      } else {
+        LOG(ERROR) << "Producer was told of a write, which shouldn't happen.";
+        DCHECK(0);

[Anand Mistry (off Chromium), 2016/01/11 06:19:34]

NOTREACHED();

[Eliot Courtney, 2016/01/13 00:00:09]

Done.

+      }
+      break;
+    case DATA_READ:
+      if (is_producer_) {
+        UpdateFromRead(command.num_bytes);
+      } else {
+        LOG(ERROR) << "Consumer was told of a read, which shouldn't happen.";
+        DCHECK(0);
+      }
+      break;
+    default:
+      LOG(ERROR) << "Shouldn't happen";
+      DCHECK(0);
+  }
 
-  return ScopedPlatformHandle(platform_handle);
+  // Handles write/read case and shared buffer becoming available case.
+  return (was_unreadable && GetReadableBytes()) ||
+         (was_unwritable && GetWritableBytes());
 }
 
 }  // namespace edk