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