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* [Bug libstdc++/65393] New: std::thread shared_ptr inefficiency
@ 2015-03-11 19:00 klemensbaum at gmail dot com
2015-03-11 19:14 ` [Bug libstdc++/65393] " redi at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: klemensbaum at gmail dot com @ 2015-03-11 19:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65393
Bug ID: 65393
Summary: std::thread shared_ptr inefficiency
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: klemensbaum at gmail dot com
The std::thread implementation passes around shared_ptr instances by value in
multiple places where they could be moved:
1)
in the function
void
thread::_M_start_thread(__shared_base_type __b)
the line
_M_start_thread(__b, nullptr);
could be changed to
_M_start_thread(std::move(__b), nullptr);
or alternatively take __shared_base_type by "universal reference" and forward
it into the other _M_start_thread overload.
2)
in the function
void
thread::_M_start_thread(__shared_base_type __b, void (*)())
the lines
__b->_M_this_ptr = __b;
int __e = __gthread_create(&_M_id._M_thread,
&execute_native_thread_routine, __b.get());
could be changed to
auto __p = __b.get();
__b->_M_this_ptr = std::move(__b);
int __e = __gthread_create(&_M_id._M_thread,
&execute_native_thread_routine, __p);
3) Finally, the use of shared_ptr seems wholly unnecessarily. This can likely
be implemented more cleanly with unique_ptr, and more efficiently, since it
avoids the extra heap space for the reference count and all of the atomic ops.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/65393] std::thread shared_ptr inefficiency
2015-03-11 19:00 [Bug libstdc++/65393] New: std::thread shared_ptr inefficiency klemensbaum at gmail dot com
@ 2015-03-11 19:14 ` redi at gcc dot gnu.org
2015-06-16 17:54 ` redi at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: redi at gcc dot gnu.org @ 2015-03-11 19:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65393
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2015-03-11
Assignee|unassigned at gcc dot gnu.org |redi at gcc dot gnu.org
Target Milestone|--- |6.0
Ever confirmed|0 |1
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Klemens from comment #0)
> could be changed to
> _M_start_thread(std::move(__b), nullptr);
>
> or alternatively take __shared_base_type by "universal reference" and
> forward it into the other _M_start_thread overload.
(They're called forwarding references now)
That would require making the function a template, for no benefit.
It should be moved.
In general, these inefficiencies are pretty tiny compared to the cost of
launching a new thread that happens immediately after.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/65393] std::thread shared_ptr inefficiency
2015-03-11 19:00 [Bug libstdc++/65393] New: std::thread shared_ptr inefficiency klemensbaum at gmail dot com
2015-03-11 19:14 ` [Bug libstdc++/65393] " redi at gcc dot gnu.org
@ 2015-06-16 17:54 ` redi at gcc dot gnu.org
2015-06-22 15:54 ` redi at gcc dot gnu.org
2015-09-29 12:56 ` redi at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: redi at gcc dot gnu.org @ 2015-06-16 17:54 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65393
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Tue Jun 16 17:53:52 2015
New Revision: 224530
URL: https://gcc.gnu.org/viewcvs?rev=224530&root=gcc&view=rev
Log:
PR libstdc++/65393
* src/c++11/thread.cc (thread::_M_make_thread): Replace shared_ptr
copies with moves.
Modified:
trunk/libstdc++-v3/ChangeLog
trunk/libstdc++-v3/src/c++11/thread.cc
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/65393] std::thread shared_ptr inefficiency
2015-03-11 19:00 [Bug libstdc++/65393] New: std::thread shared_ptr inefficiency klemensbaum at gmail dot com
2015-03-11 19:14 ` [Bug libstdc++/65393] " redi at gcc dot gnu.org
2015-06-16 17:54 ` redi at gcc dot gnu.org
@ 2015-06-22 15:54 ` redi at gcc dot gnu.org
2015-09-29 12:56 ` redi at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: redi at gcc dot gnu.org @ 2015-06-22 15:54 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65393
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Mon Jun 22 15:53:27 2015
New Revision: 224742
URL: https://gcc.gnu.org/viewcvs?rev=224742&root=gcc&view=rev
Log:
Backport from mainline
2015-06-16 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/65393
* src/c++11/thread.cc (thread::_M_make_thread): Replace shared_ptr
copies with moves.
Modified:
branches/gcc-5-branch/libstdc++-v3/ChangeLog
branches/gcc-5-branch/libstdc++-v3/src/c++11/thread.cc
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/65393] std::thread shared_ptr inefficiency
2015-03-11 19:00 [Bug libstdc++/65393] New: std::thread shared_ptr inefficiency klemensbaum at gmail dot com
` (2 preceding siblings ...)
2015-06-22 15:54 ` redi at gcc dot gnu.org
@ 2015-09-29 12:56 ` redi at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: redi at gcc dot gnu.org @ 2015-09-29 12:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65393
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution|--- |FIXED
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
shared_ptr is no longer used on trunk.
^ permalink raw reply [flat|nested] 5+ messages in thread
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2015-03-11 19:00 [Bug libstdc++/65393] New: std::thread shared_ptr inefficiency klemensbaum at gmail dot com
2015-03-11 19:14 ` [Bug libstdc++/65393] " redi at gcc dot gnu.org
2015-06-16 17:54 ` redi at gcc dot gnu.org
2015-06-22 15:54 ` redi at gcc dot gnu.org
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