[fix](scanner) Fix deadlock when scanner submit failed #40495#40640
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yiguolei merged 1 commit intoapache:branch-2.1from Sep 11, 2024
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We have dead lock when submit scanner to scheduler failed.
pstack looks like
```txt
Thread 2012 (Thread 0x7f87363fb700 (LWP 4179707) "Pipe_normal [wo"):
.h:749
```
Deallock happens with following
```cpp
Status ScannerContext::get_block_from_queue {
std::unique_lock l(_transfer_lock);
...
if (scan_task->is_eos()) {
...
} else {
// resubmit current running scanner to read the next block
submit_scan_task(scan_task);
}
}
ScannerContext::submit_scan_task(std::shared_ptr<ScanTask> scan_task) {
_scanner_scheduler->submit(shared_from_this(), scan_task);
}
void ScannerScheduler::submit(std::shared_ptr<ScannerContext> ctx,
std::shared_ptr<ScanTask> scan_task) {
...
if (auto ret = sumbit_task(); !ret) {
scan_task->set_status(Status::InternalError(
"Failed to submit scanner to scanner pool reason:" + std::string(ret.msg()) +
"|type:" + std::to_string(type)));
ctx->append_block_to_queue(scan_task);
return;
}
}
void ScannerContext::append_block_to_queue(std::shared_ptr<ScanTask> scan_task) {
...
std::lock_guard<std::mutex> l(_transfer_lock);
...
}
```
Since mutex in cpp is not re-enterable, so the scanner thread will
deadlock with itself.
This pr fix the problem by making `ScannerScheduler::submit` return a
Status instead of doing append failed task to the ScannerContext. The
caller itself will decide where resubmit the scanner or just abort the
execution of the query.
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yiguolei
approved these changes
Sep 11, 2024
3 tasks
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cherry pick from #40495