Re: [RFC} threadsafe internal profiler

On Tue, Jan 11, 2011 at 10:54 AM, Amos Jeffries <squid3_at_treenet.co.nz> wrote:
> On 11/01/11 22:08, Kinkie wrote:
>>
>> On Tue, Jan 11, 2011 at 8:03 AM, Amos Jeffries<squid3_at_treenet.co.nz>
>>  wrote:
>>>
>>> The profiler aufs assertions are caused by the profiler not being thread
>>> safe but attempting to account operations inside each of the AIO threads.
>>> Lack of thread safety is due to the stack the profiler maintains of what
>>> states are currently being counted.
>>>
>>> I don't believe we should be maintaining such a stack. Instead I think we
>>> should leverage the existing system stack by having the PROF_start(X)
>>> macro
>>> create a counter object in the local scope being counted. When the local
>>> scope exists for any reason the system stack object will be destructed
>>> and
>>> the destructor can accumulate the counters back into the global data.
>>
>> +1. I like this.
>>
>
> FWIW; I looked at coding it up. There is one major side effect with the
> change:
>
>  It seems the current profiler is trying some fancy accounting to eliminate
> time when child-scopes were operating. But only if they had their own
> counters.
>
> The proposed change will give us high level functions displayed with much
> longer running times than before. Since the new profiler scheme will account
> child run-times in with the parent function/method. However these will be
> more consistent (if not accurate) than previous outputs.

How about using thread-local storage for that, when available?
https://secure.wikimedia.org/wikipedia/en/wiki/Thread-local_storage#GCC

In other words, implementing a roll-our-own stack frame pointer-alike..

something like:
__thread statobj *current_statobj;

class statobj {
  accurate_timediff_t ticks;
  accurate_time_t started_at, created_at;
  string funcname;
  statobj * upstack;
  statobj() : ticks(0), upstack(current_statobj),
created_at(get_accurate_time()) {
   current_statobj=this;
   start();
  }
  stop() {
    ticks+=(get_accurate_time()-started_at);
  }
  start() {
    started_at=get_accurate_time();
  }
  ~statobj() {
   stop();
   report(funcname,ticks,get_accurate_time()-created_at); //get both
scope lifetime and runtime
   current_statobj=upstack;
  }
  operator new() {
    throw("only on stack, please");
  }
}

-- 
    /kinkie