Initially, IPCInternal{Request,Response} had contained IPCStreams which would
result in unecessary copying when sending the objects over IPC. The patch
makes these streams either:
1) ParentToParentStream (just a UUID)
2) ParentToChildStream (a PIPCBlobInputStream actor, acting as a handle)
3) ChildToParentStream (a real IPCStream)
These three types are union-ed together by the BodyStreamVariant IPDL structure.
This structure replaces the IPCStream members in IPCInternal{Request,Response}
so that, depending on the particular IPDL protocol, we can avoid cloning streams
and just pass handles/IDs instead.
As a side effect, this makes file-backed Response objects cloneable. Initially,
these Responses would be backed by an nsFileInputStream, which is not cloneable
outside the parent process. They are now backed by IPCBlobInputStreams, which
are cloneable.
One thing that's not really satisfactory (IMO), is the manual management of
IPCBlobInputStreamStorage so that no streams are leaked, e.g. if we store a
stream in the IPCBlobInputStreamStorage but fail to send an IPC message and
therefore fail to remove the stream from storage on the other side of the IPC
boundary (only parent-to-parent in this case).
Differential Revision: https://phabricator.services.mozilla.com/D73173
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project pages with documentation can be found at:
https://firefox-source-docs.mozilla.org/contributing/directory_structure.html
For information on how to build Mozilla from the source code and create the patch see:
https://firefox-source-docs.mozilla.org/contributing/how_to_contribute_firefox.html
If you have a question about developing Mozilla, and can't find the solution
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https://archive.mozilla.org/pub/firefox/nightly/latest-mozilla-central/
- or -
https://www.mozilla.org/firefox/channel/desktop/#nightly
Keep in mind that nightly builds, which are used by Mozilla developers for
testing, may be buggy.
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