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https://issues.apache.org/jira/browse/THRIFT-4004?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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James E. King, III resolved THRIFT-4004.
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Resolution: Invalid
Fix Version/s: 0.10.0
In the scenario you described, there would not be a deadlock.
Task #1 is added and monitor_ is signaled.
The worker does not wake up.
Task #2 inside add() would call maxMonitor_.wait() - this unlocks the mutex,
since all of the monitors are sharing the same mutex.
The worker wakes up from waiting on monitor_ because it can acquire the mutex.
It pops something off the queue. Then it sees the queue is less than the
maximum so it signals maxMonitor_. Then it unlocks the mutex to run the task.
The add() for Task #2 would wake up from maxMonitor_ and add the task.
What makes this safe today as compared to past versions is that all three
monitors share the same mutex.
> ThreadManager deadlock when adding new task
> -------------------------------------------
>
> Key: THRIFT-4004
> URL: https://issues.apache.org/jira/browse/THRIFT-4004
> Project: Thrift
> Issue Type: Bug
> Components: C++ - Library
> Affects Versions: 0.9.3
> Reporter: Liu Lin
> Assignee: James E. King, III
> Fix For: 0.10.0
>
>
> Set pendingTaskCountMax = 1.
> Add only 1 worker into ThreadManager.
> When adding task, set timeout > 0.
> If there is no task, worker thread will sleep, because
> manager_->monitor_.wait(Line 259) is called in function
> ThreadManager::Worker::run.
> Then suppose we have 2 tasks. We add the first task by calling
> ThreadManager::Impl::add, which will nofity monitor_. But before
> manager_->monitor_.wait() returns, we call ThreadManager::Impl::add again. If
> ThreadManager::Impl::add gets lock mutex_ successfully,
> ThreadManager::Worker::run will fall asleep again because it can not lock
> mutex_.
> Now we have tasks_.size() == pendingTaskCountMax_, so
> ThreadManager::Impl::add will wait on maxMonitor_(Line 462). Becasue the
> worker cannot fetch a task(because it can not lock mutex_, it will not notify
> maxMonitor_), so ThreadManager::Impl::add will wait forever.
> Now both the two threads wait for each other, result in deadlock.
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