Source code
Revision control
Copy as Markdown
Other Tools
/* -*- 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
#ifndef dom_ipc_SharedMap_h
#define dom_ipc_SharedMap_h
#include "mozilla/dom/MozSharedMapBinding.h"
#include "mozilla/AutoMemMap.h"
#include "mozilla/dom/ipc/StructuredCloneData.h"
#include "mozilla/DOMEventTargetHelper.h"
#include "mozilla/Maybe.h"
#include "mozilla/UniquePtr.h"
#include "mozilla/Variant.h"
#include "nsClassHashtable.h"
#include "nsTArray.h"
class nsIGlobalObject;
namespace mozilla::dom {
class ContentParent;
namespace ipc {
/**
* Together, the SharedMap and WritableSharedMap classes allow sharing a
* dynamically-updated, shared-memory key-value store across processes.
*
* The maps may only ever be updated in the parent process, via
* WritableSharedMap instances. When that map changes, its entire contents are
* serialized into a contiguous shared memory buffer, and broadcast to all child
* processes, which in turn update their entire map contents wholesale.
*
* Keys are arbitrary UTF-8 strings (currently exposed to JavaScript as UTF-16),
* and values are structured clone buffers. Values are eagerly encoded whenever
* they are updated, and lazily decoded each time they're read.
*
* Updates are batched. Rather than each key change triggering an immediate
* update, combined updates are broadcast after a delay. Changes are flushed
* immediately any time a new process is created. Additionally, any time a key
* is changed, a flush task is scheduled for the next time the event loop
* becomes idle. Changes can be flushed immediately by calling the flush()
* method.
*
*
* Whenever a read-only SharedMap is updated, it dispatches a "change" event.
* The event contains a "changedKeys" property with a list of all keys which
* were changed in the last update batch. Change events are never dispatched to
* WritableSharedMap instances.
*/
class SharedMap : public DOMEventTargetHelper {
using FileDescriptor = mozilla::ipc::FileDescriptor;
public:
SharedMap();
SharedMap(nsIGlobalObject* aGlobal, const FileDescriptor&, size_t,
nsTArray<RefPtr<BlobImpl>>&& aBlobs);
// Returns true if the map contains the given (UTF-8) key.
bool Has(const nsACString& name);
// If the map contains the given (UTF-8) key, decodes and returns a new copy
// of its value. Otherwise returns null.
void Get(JSContext* cx, const nsACString& name,
JS::MutableHandle<JS::Value> aRetVal, ErrorResult& aRv);
// Conversion helpers for WebIDL callers
bool Has(const nsAString& aName) { return Has(NS_ConvertUTF16toUTF8(aName)); }
void Get(JSContext* aCx, const nsAString& aName,
JS::MutableHandle<JS::Value> aRetVal, ErrorResult& aRv) {
return Get(aCx, NS_ConvertUTF16toUTF8(aName), aRetVal, aRv);
}
/**
* WebIDL iterator glue.
*/
uint32_t GetIterableLength() const { return EntryArray().Length(); }
/**
* These functions return the key or value, respectively, at the given index.
* The index *must* be less than the value returned by GetIterableLength(), or
* the program will crash.
*/
const nsString GetKeyAtIndex(uint32_t aIndex) const;
bool GetValueAtIndex(JSContext* aCx, uint32_t aIndex,
JS::MutableHandle<JS::Value> aResult) const;
/**
* Returns a copy of the read-only file descriptor which backs the shared
* memory region for this map. The file descriptor may be passed between
* processes, and used to update corresponding instances in child processes.
*/
FileDescriptor CloneMapFile() const;
/**
* Returns the size of the memory mapped region that backs this map. Must be
* passed to the SharedMap() constructor or Update() method along with the
* descriptor returned by CloneMapFile() in order to initialize or update a
* child SharedMap.
*/
size_t MapSize() const { return mMap.size(); }
/**
* Updates this instance to reflect the contents of the shared memory region
* in the given map file, and broadcasts a change event for the given set of
* changed (UTF-8-encoded) keys.
*/
void Update(const FileDescriptor& aMapFile, size_t aMapSize,
nsTArray<RefPtr<BlobImpl>>&& aBlobs,
nsTArray<nsCString>&& aChangedKeys);
JSObject* WrapObject(JSContext* aCx,
JS::Handle<JSObject*> aGivenProto) override;
protected:
~SharedMap() override = default;
class Entry {
public:
Entry(Entry&&) = delete;
explicit Entry(SharedMap& aMap, const nsACString& aName = ""_ns)
: mMap(aMap), mName(aName), mData(AsVariant(uint32_t(0))) {}
~Entry() = default;
/**
* Encodes or decodes this entry into or from the given OutputBuffer or
* InputBuffer.
*/
template <typename Buffer>
void Code(Buffer& buffer) {
DebugOnly<size_t> startOffset = buffer.cursor();
buffer.codeString(mName);
buffer.codeUint32(DataOffset());
buffer.codeUint32(mSize);
buffer.codeUint16(mBlobOffset);
buffer.codeUint16(mBlobCount);
MOZ_ASSERT(buffer.cursor() == startOffset + HeaderSize());
}
/**
* Returns the size that this entry will take up in the map header. This
* must be equal to the number of bytes encoded by Code().
*/
size_t HeaderSize() const {
return (sizeof(uint16_t) + mName.Length() + sizeof(DataOffset()) +
sizeof(mSize) + sizeof(mBlobOffset) + sizeof(mBlobCount));
}
/**
* Updates the value of this entry to the given structured clone data, of
* which it takes ownership. The passed StructuredCloneData object must not
* be used after this call.
*/
void TakeData(StructuredCloneData&&);
/**
* This is called while building a new snapshot of the SharedMap. aDestPtr
* must point to a buffer within the new snapshot with Size() bytes reserved
* for it, and `aNewOffset` must be the offset of that buffer from the start
* of the snapshot's memory region.
*
* This function copies the raw structured clone data for the entry's value
* to the new buffer, and updates its internal state for use with the new
* data. Its offset is updated to aNewOffset, and any StructuredCloneData
* object it holds is destroyed.
*
* After this call, the entry is only valid in reference to the new
* snapshot, and must not be accessed again until the SharedMap mMap has
* been updated to point to it.
*/
void ExtractData(char* aDestPtr, uint32_t aNewOffset,
uint16_t aNewBlobOffset);
// Returns the UTF-8-encoded name of the entry, which is used as its key in
// the map.
const nsCString& Name() const { return mName; }
// Decodes the entry's value into the current Realm of the given JS context
// and puts the result in aRetVal on success.
void Read(JSContext* aCx, JS::MutableHandle<JS::Value> aRetVal,
ErrorResult& aRv);
// Returns the byte size of the entry's raw structured clone data.
uint32_t Size() const { return mSize; }
private:
// Returns a pointer to the entry value's structured clone data within the
// SharedMap's mapped memory region. This is *only* valid shen mData
// contains a uint32_t.
const char* Data() const { return mMap.Data() + DataOffset(); }
// Returns the offset of the entry value's structured clone data within the
// SharedMap's mapped memory region. This is *only* valid shen mData
// contains a uint32_t.
uint32_t& DataOffset() { return mData.as<uint32_t>(); }
const uint32_t& DataOffset() const { return mData.as<uint32_t>(); }
public:
uint16_t BlobOffset() const { return mBlobOffset; }
uint16_t BlobCount() const { return mBlobCount; }
Span<const RefPtr<BlobImpl>> Blobs() {
if (mData.is<StructuredCloneData>()) {
return mData.as<StructuredCloneData>().BlobImpls();
}
return {&mMap.mBlobImpls[mBlobOffset], BlobCount()};
}
private:
// Returns the temporary StructuredCloneData object containing the entry's
// value. This is *only* value when mData contains a StructuredCloneDAta
// object.
const StructuredCloneData& Holder() const {
return mData.as<StructuredCloneData>();
}
SharedMap& mMap;
// The entry's (UTF-8 encoded) name, which serves as its key in the map.
nsCString mName;
/**
* This member provides a reference to the entry's structured clone data.
* Its type varies depending on the state of the entry:
*
* - For entries which have been snapshotted into a shared memory region,
* this is a uint32_t offset into the parent SharedMap's Data() buffer.
*
* - For entries which have been changed in a WritableSharedMap instance,
* but not serialized to a shared memory snapshot yet, this is a
* StructuredCloneData instance, containing a process-local copy of the
* data. This will be discarded the next time the map is serialized, and
* replaced with a buffer offset, as described above.
*/
Variant<uint32_t, StructuredCloneData> mData;
// The size, in bytes, of the entry's structured clone data.
uint32_t mSize = 0;
uint16_t mBlobOffset = 0;
uint16_t mBlobCount = 0;
};
const nsTArray<Entry*>& EntryArray() const;
nsTArray<RefPtr<BlobImpl>> mBlobImpls;
// Rebuilds the entry hashtable mEntries from the values serialized in the
// current snapshot, if necessary. The hashtable is rebuilt lazily after
// construction and after every Update() call, so this function must be called
// before any attempt to access mEntries.
Result<Ok, nsresult> MaybeRebuild();
void MaybeRebuild() const;
// Note: This header is included by WebIDL binding headers, and therefore
// can't include "windows.h". Since FileDescriptor.h does include "windows.h"
// on Windows, we can only forward declare FileDescriptor, and can't include
// it as an inline member.
UniquePtr<FileDescriptor> mMapFile;
// The size of the memory-mapped region backed by mMapFile, in bytes.
size_t mMapSize = 0;
mutable nsClassHashtable<nsCStringHashKey, Entry> mEntries;
mutable Maybe<nsTArray<Entry*>> mEntryArray;
// Manages the memory mapping of the current snapshot. This is initialized
// lazily after each SharedMap construction or updated, based on the values in
// mMapFile and mMapSize.
loader::AutoMemMap mMap;
bool mWritable = false;
// Returns a pointer to the beginning of the memory mapped snapshot. Entry
// offsets are relative to this pointer, and Entry objects access their
// structured clone data by indexing this pointer.
char* Data() { return mMap.get<char>().get(); }
};
class WritableSharedMap final : public SharedMap {
public:
NS_DECL_ISUPPORTS_INHERITED
NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(WritableSharedMap, SharedMap)
WritableSharedMap();
// Sets the value of the given (UTF-8 encoded) key to a structured clone
// snapshot of the given value.
void Set(JSContext* cx, const nsACString& name, JS::Handle<JS::Value> value,
ErrorResult& aRv);
// Deletes the given (UTF-8 encoded) key from the map.
void Delete(const nsACString& name);
// Conversion helpers for WebIDL callers
void Set(JSContext* aCx, const nsAString& aName, JS::Handle<JS::Value> aValue,
ErrorResult& aRv) {
return Set(aCx, NS_ConvertUTF16toUTF8(aName), aValue, aRv);
}
void Delete(const nsAString& aName) {
return Delete(NS_ConvertUTF16toUTF8(aName));
}
// Flushes any queued changes to a new snapshot, and broadcasts it to all
// child SharedMap instances.
void Flush();
// Sends the current set of shared map data to the given content process.
void SendTo(ContentParent* aContentParent) const;
/**
* Returns the read-only SharedMap instance corresponding to this
* WritableSharedMap for use in the parent process.
*/
SharedMap* GetReadOnly();
JSObject* WrapObject(JSContext* aCx,
JS::Handle<JSObject*> aGivenProto) override;
protected:
~WritableSharedMap() override = default;
private:
// The set of (UTF-8 encoded) keys which have changed, or been deleted, since
// the last snapshot.
nsTArray<nsCString> mChangedKeys;
RefPtr<SharedMap> mReadOnly;
bool mPendingFlush = false;
// Creates a new snapshot of the map, and updates all Entry instance to
// reference its data.
Result<Ok, nsresult> Serialize();
void IdleFlush();
// If there have been any changes since the last snapshot, creates a new
// serialization and broadcasts it to all child SharedMap instances.
void BroadcastChanges();
// Marks the given (UTF-8 encoded) key as having changed. This adds it to
// mChangedKeys, if not already present, and schedules a flush for the next
// time the event loop is idle.
nsresult KeyChanged(const nsACString& aName);
};
} // namespace ipc
} // namespace mozilla::dom
#endif // dom_ipc_SharedMap_h