Questions tagged [copy-on-write]
215 questions
185
votes
9 answers
What is copy-on-write?
I would like to know what copy-on-write is and what it is used for. The term is mentioned several times in the Sun JDK tutorials.
hhafez
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128
votes
7 answers
Legality of COW std::string implementation in C++11
It had been my understanding that copy-on-write is not a viable way to implement a conforming std::string in C++11, but when it came up in discussion recently I found myself unable to directly support that statement.
Am I correct that C++11 does not…
acm
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41
votes
2 answers
Does swift copy on write for all structs?
I know that swift will optimize to copy on write for arrays but will it do this for all structs? For example:
struct Point {
var x:Float = 0
}
var p1 = Point()
var p2 = p1 //p1 and p2 share the same data under the hood
p2.x += 1 //p2 now has its…
gloo
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29
votes
3 answers
Does (string) 'hard-copy' a string?
PHP uses a copy-on-modification system.
Does $a = (string) $a; ($a is a already string) modify and copy anything?
Especially, this is my problem:
Parameter 1 is mixed / I want to allow to pass non-strings and convert them to strings.
But sometimes…
mzimmer
- 523
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21
votes
5 answers
How to implement Copy-on-Write?
I want to implement a copy-on-write on my custom C++ String class, and I wonder how to.
I tried to implement some options, but they all turned out very inefficient.
fiveOthersWaiting
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20
votes
1 answer
Create copy-on-write directory on Windows 7 with NTFS
I have a directory containing source code, which I compile to produce object files. I want to quickly apply a patch and rebuild in such a way that I have simultaneous access to both the old and new object files. One way to do that is:
cd old &&…
Neil Mitchell
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18
votes
2 answers
Copy on Write with shared_ptr
So I have a simple cow_ptr. It looks something like this:
template>
struct cow_ptr:private Base{
using Base::operator*;
using Base::operator->;
using Base::operator bool;
// etc
…
Yakk - Adam Nevraumont
- 262,606
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17
votes
7 answers
Which string classes to use in C++?
we have a multi-threaded desktop application in C++ (MFC). Currently developers use either CString or std::string, probably depending on their mood. So we'd like to choose a single implementation (probably something other than those two).
MFC's…
Roman L
- 3,006
- 25
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16
votes
3 answers
Performance of function slice parameter vs global variable?
I've got the following function:
func checkFiles(path string, excludedPatterns []string) {
// ...
}
I'm wondering, since excludedPatterns never changes, should I optimize it by making the var global (and not passing it to the function every…
laurent
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15
votes
9 answers
remove elements from CopyOnWriteArrayList
I am getting an exception when I try to remove elements from CopyOnWriteArrayList using an iterator.
I have noticed that it is documented
Element-changing operations on iterators themselves (remove, set, and add) are not supported. These methods…
Bick
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15
votes
1 answer
Python multiprocessing copy-on-write behaving differently between OSX and Ubuntu
I'm trying to share objects between the parent and child process in Python. To play around with the idea, I've created a simple Python script:
from multiprocessing import Process
from os import getpid
import psutil
shared =…
chhabrakadabra
- 430
- 3
- 10
15
votes
5 answers
Does StringBuilder become immutable after a call to ToString?
I distinctly remember from the early days of .NET that calling ToString on a StringBuilder used to provide the new string object (to be returned) with the internal char buffer used by StringBuilder. This way if you constructed a huge string using…
M.S
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14
votes
5 answers
Why VC++ Strings are not reference counted?
STL standard do not require from std::string to be refcounted. But in fact most of C++
implementations provide refcounted, copy-on-write strings, allowing you passing
string by value as a primitive type. Also these implementations (at least g++)…
Artyom
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14
votes
1 answer
What is implicit sharing?
I am building a game engine library in C++. A little while back I was using Qt to build an application and was rather fascinated with its use of Implicit Sharing. I am wondering if anybody could explain this technique in greater detail or could…
Dave
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13
votes
1 answer
R: selecting subset without copying
Is there a way to select a subset from objects (data frames, matrices, vectors) without making a copy of selected data?
I work with quite large data sets, but never change them. However often for convenience I select subsets of the data to operate…
ffriend
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