Thanks every body for the detailed advise. Let me try replacing latches by condition variables. I will report the results here.
On Wed, Nov 2, 2016 at 11:54 AM, Craig Ringer <cr...@2ndquadrant.com> wrote: > On 2 November 2016 at 02:10, Robert Haas <robertmh...@gmail.com> wrote: > > On Tue, Nov 1, 2016 at 12:35 PM, Abbas Butt <abbas.b...@enterprisedb.com> > wrote: > >> Hi, > >> Consider this situation: > >> 1. I have a background worker process. > >> 2. The process creates a latch, initializes it using InitLatch & resets > it. > >> 3. It then creates a thread and passes the latch created in step 2 to > it. > >> To pass it, the process uses the last argument of pthread_create. > >> 4. The thread blocks by calling WaitLatch. > >> 5. The process after some time sets the latch using SetLatch. > >> > >> The thread does not notice that the latch has been set and keeps > waiting. > >> > >> My question is: > >> Are latches supposed to work between a process and a thread created by > that > >> process? > > > > Nothing in the entire backend is guaranteed to work if you spawn > > multiple threads within the same process. > > > > Including this. > > Yep. > > You could have the main thread wait on the latch, then signal the > other threads via appropriate pthread primitives. But you must ensure > your other threads do nothing that calls into backend code. Including > things like atexit handlers. They need to coordinate with the main > thread to do everything PostgreSQL related, and you'd need to make > sure the main thread handles all signals. That's the default for Linux > - the main thread gets first chance at all signals and other threads' > sigmasks are only checked if the main thread has masked the signal, > but that means your other threads should be sure to mask all signals > used by PostgreSQL. Good luck doing that portably. > > There are exceptions where you can call some backend functions and > macros from other threads. But you'd have to analyse each on a case by > case basis, and there's no guarantee they'll _stay_ safe. > > I'd just avoid using threads in the backend if at all possible. > > -- > Craig Ringer http://www.2ndQuadrant.com/ > PostgreSQL Development, 24x7 Support, Training & Services > -- -- *Abbas* Architect Ph: 92.334.5100153 Skype ID: gabbasb www.enterprisedb.co <http://www.enterprisedb.com/>m <http://www.enterprisedb.com/> *Follow us on Twitter* @EnterpriseDB Visit EnterpriseDB for tutorials, webinars, whitepapers <http://www.enterprisedb.com/resources-community> and more <http://www.enterprisedb.com/resources-community>
