[WasmFS] Add a hack to work around deadlocks #17869
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
|
Current dependencies on/for this PR: This comment was auto-generated by Graphite. |
kripken
reviewed
Sep 16, 2022
system/lib/wasmfs/thread_utils.h
Outdated
Comment on lines
39
to
43
| var heartbeat = () => { | ||
| _emscripten_proxy_execute_queue($0); | ||
| setTimeout(heartbeat, 50); | ||
| }; | ||
| heartbeat(); |
There was a problem hiding this comment.
Suggested change
| var heartbeat = () => { | |
| _emscripten_proxy_execute_queue($0); | |
| setTimeout(heartbeat, 50); | |
| }; | |
| heartbeat(); | |
| var intervalID = setInterval(() => { | |
| if (ABORT) { | |
| clearInterval(intervalID); | |
| } else { | |
| _emscripten_proxy_execute_queue($0); | |
| } | |
| }, 1000); |
When the main thread tries to perform a WasmFS operation that tries to acquire a lock that is already held by another thread that is trying to proxy a backend operation, deadlock can occur. Proxying depends on passing a message to a worker thread and that message has to be relayed through the main thread. When the main thread is spinning on a lock, the proxying message is not relayed and neither thread makes forward progress. Work around the issue by adding a heartbeat event on the dedicated worker thread to make it execute the queue periodically even without receiving a message from the main thread. This allows the proxying thread holding the lock to make forward progress and resolves the deadlock.
tlively
force-pushed
the
wasmfs-hacky-deadlock-fix
branch
from
92b8fcc
to
23697f3
Compare
kripken
approved these changes
Oct 31, 2022
system/lib/wasmfs/thread_utils.h
Outdated
Comment on lines
49
to
51
| }, queue.queue); | ||
|
|
||
| // Sit in the event loop performing work as it comes in. |
There was a problem hiding this comment.
This indentation looks wrong. Should the entire EM_ASM be indented two more?
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
When the main thread tries to perform a WasmFS operation that tries to acquire a
lock that is already held by another thread that is trying to proxy a backend
operation, deadlock can occur. Proxying depends on passing a message to a worker
thread and that message has to be relayed through the main thread. When the main
thread is spinning on a lock, the proxying message is not relayed and neither
thread makes forward progress.
Work around the issue by adding a heartbeat event on the dedicated worker thread
to make it execute the queue periodically even without receiving a message from
the main thread. This allows the proxying thread holding the lock to make
forward progress and resolves the deadlock.