Split the read thread support from Communication into a dedicated
ThreadedCommunication subclass. The read thread support is used only
by a subset of Communication consumers, and it adds a lot of complexity
to the base class. Furthermore, having a dedicated subclass makes it
clear whether a particular consumer needs to account for the possibility
of read thread being running or not.
The modules currently calling `StartReadThread()` are updated to use
`ThreadedCommunication`. The remaining modules use the simplified
`Communication` class.
`SBCommunication` is changed to use `ThreadedCommunication` in order
to avoid changing the public API.
`CommunicationKDP` is updated in order to (hopefully) compile with
the new code. However, I do not have a Darwin box to test it, so I've
limited the changes to the bare minimum.
`GDBRemoteCommunication` is updated to become a `Broadcaster` directly.
Since it does not inherit from `ThreadedCommunication`, its event
support no longer collides with the one used for read thread and can
be implemented cleanly. The support for
`eBroadcastBitReadThreadDidExit` is removed from the code -- since
the read thread was not used, this event was never reported.
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.llvm.org/D133251
Ensure that the ConnectionStatus and Status from
Communication::ReadThread() is correctly passed to ::Read() in order
to fix further discrepancies between ::Read() calls in non-threaded
and threaded modes.
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.llvm.org/D132577
Our (TCP) socket support is in a much better state than pipes. Use that
for testing the Communication class.
Move the CreateTCPConnectedSockets function
(SocketTestUtilities.{h,cpp}) to a place where it can be used from
Communication tests.
Harmonize the status and error values of Communication::Read() when
running with and without read thread. Prior to this change, Read()
would return eConnectionStatusSuccess if read thread was enabled
and the read timed out or reached end-of-file, rather than
the respective states that are returned if read thread was disabled.
Now, it correctly returns eConnectionStatusTimedOut
and eConnectionStatusEndOfFile, and sets the error respectively.
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.llvm.org/D132217
Add a Communication::WriteAll() that resumes Write() if the initial call
did not write all data. Use it in GDBRemoteCommunication when sending
packets in order to fix handling partial writes (i.e. just resume/retry
them rather than erring out). This fixes LLDB failures when writing
large packets to a pty.
Differential Revision: https://reviews.llvm.org/D112169
The synchronization logic in the previous had a subtle bug. Moving of
the "m_read_thread_did_exit = true" into the critical section made it
possible for some threads calling SynchronizeWithReadThread call to get
stuck. This could happen if there were already past the point where they
checked this variable. In that case, they would block on waiting for the
eBroadcastBitNoMorePendingInput event, which would never come as the
read thread was blocked on getting the synchronization mutex.
The new version moves that line out of the critical section and before
the sending of the eBroadcastBitNoMorePendingInput event, and also adds
some comments to explain why the things need to be in this sequence:
- m_read_thread_did_exit = true: prevents new threads for waiting on
events
- eBroadcastBitNoMorePendingInput: unblock any current thread waiting
for the event
- Disconnect(): close the connection. This is the only bit that needs to
be in the critical section, and this is to ensure that we don't close
the connection while the synchronizing thread is mucking with it.
Original commit message follows:
Communication::SynchronizeWithReadThread is called whenever a process
stops to ensure that we process all of its stdout before we report the
stop. If the process exits, we first call this method, and then close
the connection.
However, when the child process exits, the thread reading its stdout
will usually (but not always) read an EOF because the other end of the
pty has been closed. In response to an EOF, the Communication read
thread closes it's end of the connection too.
This can result in a race where the read thread is closing the
connection while the synchronizing thread is attempting to get its
attention via Connection::InterruptRead.
The fix is to hold the synchronization mutex while closing the
connection.
I've found this issue while tracking down a rare flake in some of the
vscode tests. I am not sure this is the cause of those failures (as I
would have expected this issue to manifest itself differently), but it
is an issue nonetheless.
The attached test demonstrates the steps needed to reproduce the race.
It will fail under tsan without this patch.
Reviewers: clayborg, JDevlieghere
Subscribers: mgorny, lldb-commits
Tags: #lldb
Differential Revision: https://reviews.llvm.org/D77295
Summary:
Communication::SynchronizeWithReadThread is called whenever a process
stops to ensure that we process all of its stdout before we report the
stop. If the process exits, we first call this method, and then close
the connection.
However, when the child process exits, the thread reading its stdout
will usually (but not always) read an EOF because the other end of the
pty has been closed. In response to an EOF, the Communication read
thread closes it's end of the connection too.
This can result in a race where the read thread is closing the
connection while the synchronizing thread is attempting to get its
attention via Connection::InterruptRead.
The fix is to hold the synchronization mutex while closing the
connection.
I've found this issue while tracking down a rare flake in some of the
vscode tests. I am not sure this is the cause of those failures (as I
would have expected this issue to manifest itself differently), but it
is an issue nonetheless.
The attached test demonstrates the steps needed to reproduce the race.
It will fail under tsan without this patch.
Reviewers: clayborg, JDevlieghere
Subscribers: mgorny, lldb-commits
Tags: #lldb
Differential Revision: https://reviews.llvm.org/D77295
Michał Górny