Make mojo_system static and mojo_system_impl a component, never use both

mojo/public/platform/native/system_thunks.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MOJO_PUBLIC_PLATFORM_NATIVE_SYSTEM_THUNKS_H_
+#define MOJO_PUBLIC_PLATFORM_NATIVE_SYSTEM_THUNKS_H_
+
+#include <stddef.h>
+
+#include "mojo/public/c/system/core.h"
+
+// The embedder needs to bind the basic Mojo Core functions of a DSO to those of
+// the embedder when loading a DSO that is dependent on mojo_system.
+// The typical usage would look like:
+// base::ScopedNativeLibrary app_library(
+//     base::LoadNativeLibrary(app_path_, &error));
+// typedef MojoResult (*MojoSetSystemThunksFn)(MojoSystemThunks*);
+// MojoSetSystemThunksFn mojo_set_system_thunks_fn =
+//     reinterpret_cast<MojoSetSystemThunksFn>(app_library.GetFunctionPointer(
+//         "MojoSetSystemThunks"));
+// MojoSystemThunks system_thunks = MojoMakeSystemThunks();
+// size_t expected_size = mojo_set_system_thunks_fn(&system_thunks);
+// if (expected_size > sizeof(MojoSystemThunks)) {
+//   LOG(ERROR)
+//       << "Invalid DSO. Expected MojoSystemThunks size: "
+//       << expected_size;
+//   break;
+// }
+
+// Structure used to bind the basic Mojo Core functions of a DSO to those of
+// the embedder.
+// This is the ABI between the embedder and the DSO. It can only have new
+// functions added to the end. No other changes are supported.
+#pragma pack(push, 8)
+struct MojoSystemThunks {
+  size_t size;  // Should be set to sizeof(MojoSystemThunks).
+  MojoTimeTicks (*GetTimeTicksNow)();
+  MojoResult (*Close)(MojoHandle handle);
+  MojoResult (*Wait)(MojoHandle handle,
+                     MojoWaitFlags flags,
+                     MojoDeadline deadline);
+  MojoResult (*WaitMany)(const MojoHandle* handles,
+                         const MojoWaitFlags* flags,
+                         uint32_t num_handles,
+                         MojoDeadline deadline);
+  MojoResult (*CreateMessagePipe)(MojoHandle* message_pipe_handle0,
+                                  MojoHandle* message_pipe_handle1);
+  MojoResult (*WriteMessage)(MojoHandle message_pipe_handle,
+                             const void* bytes,
+                             uint32_t num_bytes,
+                             const MojoHandle* handles,
+                             uint32_t num_handles,
+                             MojoWriteMessageFlags flags);
+  MojoResult (*ReadMessage)(MojoHandle message_pipe_handle,
+                            void* bytes,
+                            uint32_t* num_bytes,
+                            MojoHandle* handles,
+                            uint32_t* num_handles,
+                            MojoReadMessageFlags flags);
+  MojoResult (*CreateDataPipe)(const MojoCreateDataPipeOptions* options,
+                               MojoHandle* data_pipe_producer_handle,
+                               MojoHandle* data_pipe_consumer_handle);
+  MojoResult (*WriteData)(MojoHandle data_pipe_producer_handle,
+                          const void* elements,
+                          uint32_t* num_elements,
+                          MojoWriteDataFlags flags);
+  MojoResult (*BeginWriteData)(MojoHandle data_pipe_producer_handle,
+                               void** buffer,
+                               uint32_t* buffer_num_elements,
+                               MojoWriteDataFlags flags);
+  MojoResult (*EndWriteData)(MojoHandle data_pipe_producer_handle,
+                             uint32_t num_elements_written);
+  MojoResult (*ReadData)(MojoHandle data_pipe_consumer_handle,
+                         void* elements,
+                         uint32_t* num_elements,
+                         MojoReadDataFlags flags);
+  MojoResult (*BeginReadData)(MojoHandle data_pipe_consumer_handle,
+                              const void** buffer,
+                              uint32_t* buffer_num_elements,
+                              MojoReadDataFlags flags);
+  MojoResult (*EndReadData)(MojoHandle data_pipe_consumer_handle,
+                            uint32_t num_elements_read);
+  MojoResult (*CreateSharedBuffer)(
+      const MojoCreateSharedBufferOptions* options,
+      uint64_t num_bytes,
+      MojoHandle* shared_buffer_handle);
+  MojoResult (*DuplicateBufferHandle)(
+      MojoHandle buffer_handle,
+      const MojoDuplicateBufferHandleOptions* options,
+      MojoHandle* new_buffer_handle);
+  MojoResult (*MapBuffer)(MojoHandle buffer_handle,
+                          uint64_t offset,
+                          uint64_t num_bytes,
+                          void** buffer,
+                          MojoMapBufferFlags flags);
+  MojoResult (*UnmapBuffer)(void* buffer);
+};
+#pragma pack(pop)
+
+// Intended to be called from the embedder. Returns a |MojoCore| initialized
+// to contain pointers to each of the embedder's MojoCore functions.
+inline MojoSystemThunks MojoMakeSystemThunks() {
+  MojoSystemThunks system_thunks = {
+    sizeof(MojoSystemThunks),
+    MojoGetTimeTicksNow,
+    MojoClose,
+    MojoWait,
+    MojoWaitMany,
+    MojoCreateMessagePipe,
+    MojoWriteMessage,
+    MojoReadMessage,
+    MojoCreateDataPipe,
+    MojoWriteData,
+    MojoBeginWriteData,
+    MojoEndWriteData,
+    MojoReadData,
+    MojoBeginReadData,
+    MojoEndReadData,
+    MojoCreateSharedBuffer,
+    MojoDuplicateBufferHandle,
+    MojoMapBuffer,
+    MojoUnmapBuffer
+  };
+  return system_thunks;
+}
+
+// Use this type for the function found by dynamically discovering it in
+// a DSO linked with mojo_system. For example:
+// MojoSetSystemThunksFn mojo_set_system_thunks_fn =
+//     reinterpret_cast<MojoSetSystemThunksFn>(app_library.GetFunctionPointer(
+//         "MojoSetSystemThunks"));
+// The expected size of |system_thunks} is returned.
+// The contents of |system_thunks| are copied.
+typedef size_t (*MojoSetSystemThunksFn)(const MojoSystemThunks* system_thunks);
+
+#endif  // MOJO_PUBLIC_PLATFORM_NATIVE_SYSTEM_THUNKS_H_