Re: C++ Threads, what's the status quo?

"Peter Dimov" <>
8 Jan 2007 15:30:59 -0500
Le Chaud Lapin wrote:

James Kanze wrote:

Which explains why so many programmers get it wrong. (The
people who implemented std::basic_string in g++ are not idiots;
they're some of the more gifted programmers I know. Never the
less, there is a threading error in the code.)

There is no "threading" error in the code. If I write

int x == 10;

int thread1 ();
int thread2 ();

...and let those two threads fiddle with x without the protection of
mutual-exclusion, there will be contention. Are you saying that the
people who designed std:basic_string designed it expecting there would
be no contention?

It's subtler than that. If you let the two threads read x without
changing it, do you expect problems?

Consider the similar example:

char x[] = "Test";

void thread1()
   char a = x[0];

void thread2()
   char b = x[0];

Do you expect problems here?

Now replace the definition of x with:

std::string x( "Test" );

James Kanze argues that the code remains correct, and that g++ is in
error to not work. Before jumping to conclusions about his
understanding of the threading issues, you first need to understand
what he's saying. (I happen to disagree with him that the code is
correct. Either way, one of the goals of the future C++ standard is to
resolve these issues by specifying the thread safety level of the
standard library components.)

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