Re: avoiding deadlocks on client handle close w/ python/c api
I've constructed a simple example just using the zkpython library with condition variables, that will deadlock. I've filed a new ticket for it, https://issues.apache.org/jira/browse/ZOOKEEPER-763 the gdb stack traces look suspiciously like the ones in 591, but sans the watchers. https://issues.apache.org/jira/browse/ZOOKEEPER-591 the attached example on the ticket will deadlock in zk 3.3.0 (which has the fix for 591) and trunk. -kapil On Mon, May 3, 2010 at 9:48 PM, Kapil Thangavelu kapil.f...@gmail.comwrote: Hi Folks, I'm constructing an async api on top of the zookeeper python bindings for twisted. The intent was to make a thin wrapper that would wrap the existing async api with one that allows for integration with the twisted python event loop (http://www.twistedmatrix.com) primarily using the async apis. One issue i'm running into while developing a unit tests, deadlocks occur if we attempt to close a handle while there are any outstanding async requests (aget, acreate, etc). Normally on close both the io thread terminates and the completion thread are terminated and joined, however w\ith outstanding async requests, the completion thread won't be in a joinable state, and we effectively hang when the main thread does the join. I'm curious if this would be considered bug, afaics ideal behavior would be on close of a handle, to effectively clear out any remaining callbacks and let the completion thread terminate. i've tried adding some bookkeeping to the api to guard against closing while there is an outstanding completion request, but its an imperfect solution do to the nature of the event loop integration. The problem is that the python callback invoked by the completion thread in turn schedules a function for the main thread. In twisted the api for this is implemented by appending the function to a list attribute on the reactor and then writing a byte to a pipe to wakeup the main thread. If a thread switch to the main thread occurs before the completion thread callback returns, the scheduled function runs and the rest of the application keeps processing, of which the last step for the unit tests is to close the connection, which results in a deadlock. i've included some of the client log and gdb stack traces from a deadlock'd client process. thanks, Kapil
Re: avoiding deadlocks on client handle close w/ python/c api
Thanks Kapil, Mahadev perhaps you could take a look at this as well? Patrick On 05/04/2010 06:36 AM, Kapil Thangavelu wrote: I've constructed a simple example just using the zkpython library with condition variables, that will deadlock. I've filed a new ticket for it, https://issues.apache.org/jira/browse/ZOOKEEPER-763 the gdb stack traces look suspiciously like the ones in 591, but sans the watchers. https://issues.apache.org/jira/browse/ZOOKEEPER-591 the attached example on the ticket will deadlock in zk 3.3.0 (which has the fix for 591) and trunk. -kapil On Mon, May 3, 2010 at 9:48 PM, Kapil Thangavelukapil.f...@gmail.comwrote: Hi Folks, I'm constructing an async api on top of the zookeeper python bindings for twisted. The intent was to make a thin wrapper that would wrap the existing async api with one that allows for integration with the twisted python event loop (http://www.twistedmatrix.com) primarily using the async apis. One issue i'm running into while developing a unit tests, deadlocks occur if we attempt to close a handle while there are any outstanding async requests (aget, acreate, etc). Normally on close both the io thread terminates and the completion thread are terminated and joined, however w\ith outstanding async requests, the completion thread won't be in a joinable state, and we effectively hang when the main thread does the join. I'm curious if this would be considered bug, afaics ideal behavior would be on close of a handle, to effectively clear out any remaining callbacks and let the completion thread terminate. i've tried adding some bookkeeping to the api to guard against closing while there is an outstanding completion request, but its an imperfect solution do to the nature of the event loop integration. The problem is that the python callback invoked by the completion thread in turn schedules a function for the main thread. In twisted the api for this is implemented by appending the function to a list attribute on the reactor and then writing a byte to a pipe to wakeup the main thread. If a thread switch to the main thread occurs before the completion thread callback returns, the scheduled function runs and the rest of the application keeps processing, of which the last step for the unit tests is to close the connection, which results in a deadlock. i've included some of the client log and gdb stack traces from a deadlock'd client process. thanks, Kapil
Re: avoiding deadlocks on client handle close w/ python/c api
Sure, Ill take a look at it. Thanks mahadev On 5/4/10 2:32 PM, Patrick Hunt ph...@apache.org wrote: Thanks Kapil, Mahadev perhaps you could take a look at this as well? Patrick On 05/04/2010 06:36 AM, Kapil Thangavelu wrote: I've constructed a simple example just using the zkpython library with condition variables, that will deadlock. I've filed a new ticket for it, https://issues.apache.org/jira/browse/ZOOKEEPER-763 the gdb stack traces look suspiciously like the ones in 591, but sans the watchers. https://issues.apache.org/jira/browse/ZOOKEEPER-591 the attached example on the ticket will deadlock in zk 3.3.0 (which has the fix for 591) and trunk. -kapil On Mon, May 3, 2010 at 9:48 PM, Kapil Thangavelukapil.f...@gmail.comwrote: Hi Folks, I'm constructing an async api on top of the zookeeper python bindings for twisted. The intent was to make a thin wrapper that would wrap the existing async api with one that allows for integration with the twisted python event loop (http://www.twistedmatrix.com) primarily using the async apis. One issue i'm running into while developing a unit tests, deadlocks occur if we attempt to close a handle while there are any outstanding async requests (aget, acreate, etc). Normally on close both the io thread terminates and the completion thread are terminated and joined, however w\ith outstanding async requests, the completion thread won't be in a joinable state, and we effectively hang when the main thread does the join. I'm curious if this would be considered bug, afaics ideal behavior would be on close of a handle, to effectively clear out any remaining callbacks and let the completion thread terminate. i've tried adding some bookkeeping to the api to guard against closing while there is an outstanding completion request, but its an imperfect solution do to the nature of the event loop integration. The problem is that the python callback invoked by the completion thread in turn schedules a function for the main thread. In twisted the api for this is implemented by appending the function to a list attribute on the reactor and then writing a byte to a pipe to wakeup the main thread. If a thread switch to the main thread occurs before the completion thread callback returns, the scheduled function runs and the rest of the application keeps processing, of which the last step for the unit tests is to close the connection, which results in a deadlock. i've included some of the client log and gdb stack traces from a deadlock'd client process. thanks, Kapil
