зеркало из https://github.com/mozilla/gecko-dev.git
103 строки
3.7 KiB
Plaintext
103 строки
3.7 KiB
Plaintext
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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include protocol PBackground;
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using struct mozilla::null_t
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from "ipc/IPCMessageUtils.h";
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namespace mozilla {
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namespace dom {
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struct LSRequestPreloadDatastoreResponse
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{
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};
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struct LSRequestPrepareDatastoreResponse
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{
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uint64_t datastoreId;
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};
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struct LSRequestPrepareObserverResponse
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{
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uint64_t observerId;
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};
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/**
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* Discriminated union which can contain an error code (`nsresult`) or
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* particular request response.
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*/
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union LSRequestResponse
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{
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nsresult;
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LSRequestPreloadDatastoreResponse;
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LSRequestPrepareDatastoreResponse;
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LSRequestPrepareObserverResponse;
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};
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/**
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* An asynchronous protocol for issuing requests that are used in a synchronous
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* fashion by LocalStorage via LSObject's RequestHelper mechanism. This differs
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* from LSSimpleRequest which is implemented and used asynchronously.
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*
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* See `PBackgroundLSSharedTypes.ipdlh` for more on the request types, the
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* response types above for their corresponding responses, and `RequestHelper`
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* for more on the usage and lifecycle of this mechanism.
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*/
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protocol PBackgroundLSRequest
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{
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manager PBackground;
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parent:
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// The Cancel message is used to avoid a possible dead lock caused by a CPOW
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// sending a synchronous message from the main thread in the chrome process
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// to the main thread in the content process at the time we are blocking
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// the main thread in the content process to handle a request.
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// We use the PBackground thread on the parent side to handle requests, but
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// sometimes we need to get information from principals and that's currently
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// only possible on the main thread. So if the main thread in the chrome
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// process is blocked by a CPOW operation, our request must wait for the CPOW
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// operation to complete. However the CPOW operation can't complete either
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// because we are blocking the main thread in the content process.
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// The dead lock is prevented by canceling our nested event loop in the
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// content process when we receive a synchronous IPC message from the parent.
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//
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// Note that cancellation isn't instantaneous. It's just an asynchronous flow
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// that definitely doesn't involve the main thread in the parent process, so
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// we're guaranteed to unblock the main-thread in the content process and
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// allow the sync IPC to make progress. When Cancel() is received by the
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// parent, it will Send__delete__. The child will either send Cancel or
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// Finish, but not both.
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async Cancel();
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/**
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* Sent by the child in response to Ready, requesting that __delete__ be sent
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* with the result. The child will either send Finish or Cancel, but not
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* both. No further message will be sent from the child after invoking one.
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*/
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async Finish();
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child:
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/**
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* The deletion is sent with the result of the request directly in response to
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* either Cancel or Finish.
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*/
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async __delete__(LSRequestResponse response);
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/**
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* Sent by the parent when it has completed whatever async stuff it needs to
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* do and is ready to send the results. It then awaits the Finish() call to
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* send the results. This may seem redundant, but it's not. If the
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* __delete__ was sent directly, it's possible there could be a race where
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* Cancel() would be received by the parent after it had already sent
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* __delete__. (Which may no longer be fatal thanks to improvements to the
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* IPC layer, but it would still lead to warnings, etc. And we don't
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* expect PBackground to be highly contended nor the DOM File thread.)
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*/
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async Ready();
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};
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} // namespace dom
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} // namespace mozilla
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