Re: libstdc++/4960: std::string slow to append individual characters

Re: libstdc++/4960: std::string slow to append individual characters

[pme]

The following reply was made to PR libstdc++/4960; it has been noted by GNATS.

From: pme@gcc.gnu.org
To: gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org, gcc-prs@gcc.gnu.org,
  martin@v.loewis.de, nobody@gcc.gnu.org
Cc:  
Subject: Re: libstdc++/4960: std::string slow to append individual characters
Date: 27 Nov 2001 23:33:03 -0000

 Synopsis: std::string slow to append individual characters
 
 State-Changed-From-To: open->analyzed
 State-Changed-By: pme
 State-Changed-When: Tue Nov 27 15:33:02 2001
 State-Changed-Why:
     This exact topic has been under discussion on the
     libstdc++-v3 mailing list during the last 48 hours (and
     for quite a while before then, too).  Please check the
     archives and try out the patches under consideration;
     they will be included in some form or another in 3.1
     (and possibly 3.0.x also).
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=4960&database=gcc

Re: libstdc++/4960: std::string slow to append individual characters

[paolo]

The following reply was made to PR libstdc++/4960; it has been noted by GNATS.

From: paolo@gcc.gnu.org
To: gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org, gcc-prs@gcc.gnu.org,
  martin@v.loewis.de, nobody@gcc.gnu.org, paolo@gcc.gnu.org
Cc:  
Subject: Re: libstdc++/4960: std::string slow to append individual characters
Date: 8 Dec 2001 09:52:46 -0000

 Synopsis: std::string slow to append individual characters
 
 Responsible-Changed-From-To: unassigned->paolo
 Responsible-Changed-By: paolo
 Responsible-Changed-When: Sat Dec  8 01:52:46 2001
 Responsible-Changed-Why:
     Taking care of it.	
 State-Changed-From-To: feedback->closed
 State-Changed-By: paolo
 State-Changed-When: Sat Dec  8 01:52:46 2001
 State-Changed-Why:
     Fixed.
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=4960&database=gcc

Re: libstdc++/4960: std::string slow to append individual characters

[paolo]

Synopsis: std::string slow to append individual characters

Responsible-Changed-From-To: unassigned->paolo
Responsible-Changed-By: paolo
Responsible-Changed-When: Sat Dec  8 01:52:46 2001
Responsible-Changed-Why:
    Taking care of it.	
State-Changed-From-To: feedback->closed
State-Changed-By: paolo
State-Changed-When: Sat Dec  8 01:52:46 2001
State-Changed-Why:
    Fixed.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=4960&database=gcc

Re: libstdc++/4960: std::string slow to append individual characters

[paolo]

The following reply was made to PR libstdc++/4960; it has been noted by GNATS.

From: paolo@gcc.gnu.org
To: gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org, gcc-prs@gcc.gnu.org,
  martin@v.loewis.de, nobody@gcc.gnu.org
Cc:  
Subject: Re: libstdc++/4960: std::string slow to append individual characters
Date: 5 Dec 2001 08:40:47 -0000

 Synopsis: std::string slow to append individual characters
 
 State-Changed-From-To: analyzed->feedback
 State-Changed-By: paolo
 State-Changed-When: Wed Dec  5 00:40:47 2001
 State-Changed-Why:
     Fetch a current 3.1 snapshot and benchmark again. You
     should notice a definite improvement.
     However, the final solution to the problem is an
     exponential growth policy. Patch for this posted in:
     http://gcc.gnu.org/ml/libstdc++/2001-12/msg00007.html
     Can you try it?
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=4960&database=gcc

Re: libstdc++/4960: std::string slow to append individual characters

[paolo]

Synopsis: std::string slow to append individual characters

State-Changed-From-To: analyzed->feedback
State-Changed-By: paolo
State-Changed-When: Wed Dec  5 00:40:47 2001
State-Changed-Why:
    Fetch a current 3.1 snapshot and benchmark again. You
    should notice a definite improvement.
    However, the final solution to the problem is an
    exponential growth policy. Patch for this posted in:
    http://gcc.gnu.org/ml/libstdc++/2001-12/msg00007.html
    Can you try it?

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=4960&database=gcc

Re: libstdc++/4960: std::string slow to append individual characters

[pme]

Synopsis: std::string slow to append individual characters

State-Changed-From-To: open->analyzed
State-Changed-By: pme
State-Changed-When: Tue Nov 27 15:33:02 2001
State-Changed-Why:
    This exact topic has been under discussion on the
    libstdc++-v3 mailing list during the last 48 hours (and
    for quite a while before then, too).  Please check the
    archives and try out the patches under consideration;
    they will be included in some form or another in 3.1
    (and possibly 3.0.x also).

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=4960&database=gcc

libstdc++/4960: std::string slow to append individual characters

[martin]

>Number:         4960
>Category:       libstdc++
>Synopsis:       std::string slow to append individual characters
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Tue Nov 27 15:06:00 PST 2001
>Closed-Date:
>Last-Modified:
>Originator:     Martin v. Loewis
>Release:        3.1 20010813 (experimental)
>Organization:
HUB
>Environment:
System: Linux mira 2.4.10-4GB #1 Tue Sep 25 12:33:54 GMT 2001 i686 unknown
Architecture: i686

	
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: /usr/src/egcs/configure --prefix=/usr/local/newabi --enable-shared --enable-threads --enable-languages=c,c++,java
>Description:
In gcc 2.95, adding one character after another to an std::string resulted in infrequent
memory allocations, as the implementation would reserve sufficient memory. In libstdc++ v3,
each append invocation will cause reallocation (and copying of the existing string) once
the reserve is exhausted.
>How-To-Repeat:
Compile and benchmark the following program with both gcc 2.95 and gcc 3 on the same machine.
On a 900MHz Pentium III, the 2.95 compilation result needs 0.01s, the gcc 3 result needs 4.0s.

#include <string>
#include <stdio.h>

int main()
{
	std::string s;
	int i;
	for(i=0;i<100000;i++){
		//printf("%d %d\n",i,s.capacity());
		s+=" ";
	}
}
>Fix:
	Add a reserve larger than the current size in std::string::append.
        The strategy of libstdc++ 2 (using the nearest power of 2) seems reasonable.
>Release-Note:
>Audit-Trail:
>Unformatted: