js/xpconnect/src/XPCSelfHostedShmem.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef xpcselfhostedshmem_h___
   8 #define xpcselfhostedshmem_h___
   9
  10 #include "base/shared_memory.h"
  11 #include "mozilla/UniquePtr.h"
  12 #include "mozilla/UniquePtrExtensions.h"
  13 #include "mozilla/Span.h"
  14 #include "mozilla/StaticPtr.h"
  15 #include "nsIMemoryReporter.h"
  16 #include "nsIObserver.h"
  17 #include "nsIThread.h"
  18
  19 namespace xpc {
  20
  21 // This class is a singleton which holds a file-mapping of the Self Hosted
  22 // Stencil XDR, to be shared by the parent process with all the child processes.
  23 //
  24 // It is either initialized by the parent process by monitoring when the Self
  25 // hosted stencil is produced, or by the content process by reading a shared
  26 // memory-mapped file.
  27 class SelfHostedShmem final : public nsIMemoryReporter {
  28  public:
  29   NS_DECL_THREADSAFE_ISUPPORTS
  30   NS_DECL_NSIMEMORYREPORTER
  31
  32   // NOTE: This type is identical to JS::SelfHostedCache, but we repeat it to
  33   // avoid including JS engine API in ipc code.
  34   using ContentType = mozilla::Span<const uint8_t>;
  35
  36   static SelfHostedShmem& GetSingleton();
  37
  38   // Initialize this singleton with the content of the Self-hosted Stencil XDR.
  39   // This will be used to initialize the shared memory which would hold a copy.
  40   //
  41   // This function is not thread-safe and should be call at most once and from
  42   // the main thread.
  43   void InitFromParent(ContentType aXdr);
  44
  45   // Initialize this singleton with the content coming from the parent process,
  46   // using a file handle which maps to the memory pages of the parent process.
  47   //
  48   // This function is not thread-safe and should be call at most once and from
  49   // the main thread.
  50   [[nodiscard]] bool InitFromChild(base::SharedMemoryHandle aHandle,
  51                                    size_t aLen);
  52
  53   // Return a span over the read-only XDR content of the self-hosted stencil.
  54   ContentType Content() const;
  55
  56   // Return the file handle which is under which the content is mapped.
  57   const mozilla::UniqueFileHandle& Handle() const;
  58
  59   // Register this class to the memory reporter service.
  60   void InitMemoryReporter();
  61
  62   // Unregister this class from the memory reporter service, and delete the
  63   // memory associated with the shared memory. As the memory is borrowed by the
  64   // JS engine, this function should be called after JS_Shutdown.
  65   //
  66   // NOTE: This is not using the Observer service which would call Shutdown
  67   // while JS code might still be running during shutdown process.
  68   static void Shutdown();
  69
  70  private:
  71   SelfHostedShmem() = default;
  72   ~SelfHostedShmem() = default;
  73
  74   static mozilla::StaticRefPtr<SelfHostedShmem> sSelfHostedXdr;
  75
  76   // read-only file Handle used to transfer from the parent process to content
  77   // processes.
  78   mozilla::UniqueFileHandle mHandle;
  79
  80   // Shared memory used by JS runtime initialization.
  81   mozilla::UniquePtr<base::SharedMemory> mMem;
  82
  83   // Length of the content within the shared memory.
  84   size_t mLen = 0;
  85 };
  86
  87 }  // namespace xpc
  88
  89 #endif  // !xpcselfhostedshmem_h___