is it safe to generate profiles from multiple concurrent processes?

is it safe to generate profiles from multiple concurrent processes?

[Vincenzo Innocente]

I have built a library with -fprofile-generate. 
Now I want to generate profiles using various applications that link that library.

My understanding is that it is safe to run a multi-thread process to populate the profiles.
It is unclear to me if one can safely run multiple processes concurrently.

is there any risk of corruption or overwriting of the various "gcda” files if different processes attempt to write on them?
If safe I can easily speed up the generation of profiles by orders of magnitude.

 thanks,
     vincenzo

Re: is it safe to generate profiles from multiple concurrent processes?

[Markus Trippelsdorf]

On 2014.06.25 at 11:35 +0200, Vincenzo Innocente wrote:
> I have built a library with -fprofile-generate.  Now I want to
> generate profiles using various applications that link that library.
> 
> My understanding is that it is safe to run a multi-thread process to
> populate the profiles.
> It is unclear to me if one can safely run multiple processes concurrently.
> 
> is there any risk of corruption or overwriting of the various "gcda”
> files if different processes attempt to write on them?  If safe I can
> easily speed up the generation of profiles by orders of magnitude.

The gcda files are accessed by proper locks, so you should be save.
(See gcc/gcov-io.c).

-- 
Markus

Re: is it safe to generate profiles from multiple concurrent processes?

[Arbol One]

I would like to change this code
------
#include <fstream>
int main () {
  std::fstream fs;
  fs.open ("test.txt", std::fstream::in | std::fstream::out | 
std::fstream::app);
  fs << " more lorem ipsum";
  fs.close();
  return 0;
}
-------
To look like this
#include <fstream>
int main () {
  using my_read = std::fstream::in; //<== Error: expected type-specifier
  std::fstream fs;
  fs.open ("test.txt", my_read | std::fstream::out; | std::fstream::app);
  fs << " more lorem ipsum";
  fs.close();
  return 0;
}

What am I doing wrong?

-----Original Message----- 
From: Markus Trippelsdorf
Sent: Wednesday, June 25, 2014 7:59 AM
To: Vincenzo Innocente
Cc: gcc-help@gcc.gnu.org
Subject: Re: is it safe to generate profiles from multiple concurrent 
processes?

On 2014.06.25 at 11:35 +0200, Vincenzo Innocente wrote:
> I have built a library with -fprofile-generate.  Now I want to
> generate profiles using various applications that link that library.
>
> My understanding is that it is safe to run a multi-thread process to
> populate the profiles.
> It is unclear to me if one can safely run multiple processes concurrently.
>
> is there any risk of corruption or overwriting of the various "gcda”
> files if different processes attempt to write on them?  If safe I can
> easily speed up the generation of profiles by orders of magnitude.

The gcda files are accessed by proper locks, so you should be save.
(See gcc/gcov-io.c).

-- 
Markus 

Re: is it safe to generate profiles from multiple concurrent processes?

[Jonathan Wakely]

On 25 June 2014 14:13, Arbol One wrote:

Please don't hijack other people's threads for unrelated questions.


> To look like this
> #include <fstream>
> int main () {
>  using my_read = std::fstream::in; //<== Error: expected type-specifier

"using" declares a typedef, not a variable.

Try:

   auto my_read = ...

Re: is it safe to generate profiles from multiple concurrent processes?

[Vincenzo Innocente]

> std::fstream::in is not a type 

the error is indeed 
error: ‘in’ in ‘std::fstream {aka class std::basic_fstream<char>}’ does not name a type

btw  you have a spurious “;” before "|"

I think you are confusing the usage of “using” and “auto” keywords

this compiles

#include <fstream>
int main () {
auto && my_read = std::fstream::in;
std::fstream fs;
fs.open ("test.txt", my_read | std::fstream::out | std::fstream::app);
fs << " more lorem ipsum";
fs.close();
return 0;
}


On 25 Jun, 2014, at 3:13 PM, Arbol One <arbolone@hotmail.ca> wrote:

> #include <fstream>
> int main () {
> using my_read = std::fstream::in; //<== Error: expected type-specifier
> std::fstream fs;
> fs.open ("test.txt", my_read | std::fstream::out; | std::fstream::app);
> fs << " more lorem ipsum";
> fs.close();
> return 0;
> }