[webkit-dev] When should I use AtomicString vs String?
I hope this isn't a stupid question, but I can't find any references to what the difference between AtomicString and String is. It looks like AtomicString is generally preferred, but I don't know why. Can someone fill me in on this? Is there any refences for the classes in WTF? signature.asc Description: OpenPGP digital signature ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] When should I use AtomicString vs String?
It is faster to compare and hash AtomicString than regular Strings. On Fri, May 31, 2013 at 5:57 PM, Brendan Long s...@brendanlong.com wrote: I hope this isn't a stupid question, but I can't find any references to what the difference between AtomicString and String is. It looks like AtomicString is generally preferred, but I don't know why. Can someone fill me in on this? Is there any refences for the classes in WTF? ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev -- Daker Fernandes Pinheiro http://codecereal.blogspot.com ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] When should I use AtomicString vs String?
Are there any advantages to String over AtomicString? On Fri, May 31, 2013 at 11:14 PM, Daker Pinheiro daker.pinhe...@openbossa.org wrote: It is faster to compare and hash AtomicString than regular Strings. On Fri, May 31, 2013 at 5:57 PM, Brendan Long s...@brendanlong.comwrote: I hope this isn't a stupid question, but I can't find any references to what the difference between AtomicString and String is. It looks like AtomicString is generally preferred, but I don't know why. Can someone fill me in on this? Is there any refences for the classes in WTF? ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev -- Daker Fernandes Pinheiro http://codecereal.blogspot.com ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] When should I use AtomicString vs String?
So should I just never use String and always use AtomicString? On 05/31/2013 03:14 PM, Daker Pinheiro wrote: It is faster to compare and hash AtomicString than regular Strings. On Fri, May 31, 2013 at 5:57 PM, Brendan Long s...@brendanlong.com mailto:s...@brendanlong.com wrote: I hope this isn't a stupid question, but I can't find any references to what the difference between AtomicString and String is. It looks like AtomicString is generally preferred, but I don't know why. Can someone fill me in on this? Is there any refences for the classes in WTF? ___ webkit-dev mailing list webkit-dev@lists.webkit.org mailto:webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev -- Daker Fernandes Pinheiro http://codecereal.blogspot.com signature.asc Description: OpenPGP digital signature ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] When should I use AtomicString vs String?
On May 31, 2013, at 1:57 PM, Brendan Long s...@brendanlong.com wrote: I hope this isn't a stupid question, but I can't find any references to what the difference between AtomicString and String is. WTF::AtomicString is a class that has four differences from the normal WTF::String class: 1) It’s more expensive to create a new atomic string than a non-atomic string; doing so requires a lookup in a per-thread atomic string hash table. 2) It’s very inexpensive to compare one atomic string with another. The cost is just a pointer comparison. The actual string length and data don’t need to be compared, because on any one thread no AtomicString can be equal to any other AtomicString. 3) If a particular string already exists in the atomic string table, allocating another string that is equal to it does not cost any additional memory. The atomic string is shared and the cost is looking it up in the per-thread atomic string hash table and incrementing its reference count. 4) There are special considerations if you want to use an atomic string on a thread other than the one it was created on since each thread has its own atomic string hash table. Generally speaking, we use AtomicString to make string comparisons fast and to save memory when many equal strings are likely to be allocated. For example, we use AtomicString for HTML attribute names so we can compare them quickly, and for both HTML attribute names and values since it’s common to have many identical ones and we save memory. It’s not a good idea to spend the extra cost to construct an AtomicString if neither the comparison nor the memory savings applies. It’s unnecessarily costly to convert an atomic string to a non-atomic string and then back to an atomic string, since it requires an additional hash table lookup. Thus if you’re starting with an atomic string it’s best to keep the value in variables of type AtomicString and AtomicStringImpl* if possible. -- Darin ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] When should I use AtomicString vs String?
On Fri, May 31, 2013 at 3:18 PM, Darin Adler da...@apple.com wrote:
On May 31, 2013, at 1:57 PM, Brendan Long s...@brendanlong.com wrote:
I hope this isn't a stupid question, but I can't find any references to what
the difference between AtomicString and String is.
WTF::AtomicString is a class that has four differences from the normal
WTF::String class:
1) It’s more expensive to create a new atomic string than a non-atomic
string; doing so requires a lookup in a per-thread atomic string hash table.
2) It’s very inexpensive to compare one atomic string with another. The cost
is just a pointer comparison. The actual string length and data don’t need to
be compared, because on any one thread no AtomicString can be equal to any
other AtomicString.
3) If a particular string already exists in the atomic string table,
allocating another string that is equal to it does not cost any additional
memory. The atomic string is shared and the cost is looking it up in the
per-thread atomic string hash table and incrementing its reference count.
4) There are special considerations if you want to use an atomic string on a
thread other than the one it was created on since each thread has its own
atomic string hash table.
Generally speaking, we use AtomicString to make string comparisons fast and
to save memory when many equal strings are likely to be allocated. For
example, we use AtomicString for HTML attribute names so we can compare them
quickly, and for both HTML attribute names and values since it’s common to
have many identical ones and we save memory.
It’s not a good idea to spend the extra cost to construct an AtomicString if
neither the comparison nor the memory savings applies.
It’s unnecessarily costly to convert an atomic string to a non-atomic string
and then back to an atomic string, since it requires an additional hash table
lookup. Thus if you’re starting with an atomic string it’s best to keep the
value in variables of type AtomicString and AtomicStringImpl* if possible.
I don't mean to intrude, but I believe we store a bit on StringImpl
that makes conversion from String and StringImpl to AtomicString fast
if the underlying StringImpl is already in the AtomicStringTable:
https://trac.webkit.org/browser/trunk/Source/WTF/wtf/text/AtomicString.h#L185
ALWAYS_INLINE static PassRefPtrStringImpl add(StringImpl* r)
{
if (!r || r-isAtomic())
return r;
return addSlowCase(r);
}
Adam
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Re: [webkit-dev] When should I use AtomicString vs String?
On May 31, 2013, at 3:27 PM, Adam Barth aba...@webkit.org wrote: I believe we store a bit on StringImpl that makes conversion from String and StringImpl to AtomicString fast if the underlying StringImpl is already in the AtomicStringTable. Good point. Converting back to an atomic string costs only a single bit test and branch now; it’s almost free. My mistake. -- Darin ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] When should I use AtomicString vs String?
We shouldn't use AtomicString if the string we're about to create doesn't get shared across multiple AtomicStrings. For example, if we had used AtomicString for the strings inside Text nodes, then we may end up filling up the atomic string table with all these really long strings that don't typically appear more than once. It also slows down the hash map look up for all other atomic strings. On Fri, May 31, 2013 at 3:00 PM, Brendan Long s...@brendanlong.com wrote: So should I just never use String and always use AtomicString? On 05/31/2013 03:14 PM, Daker Pinheiro wrote: It is faster to compare and hash AtomicString than regular Strings. On Fri, May 31, 2013 at 5:57 PM, Brendan Long s...@brendanlong.comwrote: I hope this isn't a stupid question, but I can't find any references to what the difference between AtomicString and String is. It looks like AtomicString is generally preferred, but I don't know why. Can someone fill me in on this? Is there any refences for the classes in WTF? ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev -- Daker Fernandes Pinheiro http://codecereal.blogspot.com ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] When should I use AtomicString vs String?
This thread contains really useful information, so I've created a new topic on https://trac.webkit.org/wiki/EfficientStrings and pointed to here. Best regards, Rafael On Fri, May 31, 2013 at 8:32 PM, Ryosuke Niwa rn...@webkit.org wrote: We shouldn't use AtomicString if the string we're about to create doesn't get shared across multiple AtomicStrings. For example, if we had used AtomicString for the strings inside Text nodes, then we may end up filling up the atomic string table with all these really long strings that don't typically appear more than once. It also slows down the hash map look up for all other atomic strings. On Fri, May 31, 2013 at 3:00 PM, Brendan Long s...@brendanlong.comwrote: So should I just never use String and always use AtomicString? On 05/31/2013 03:14 PM, Daker Pinheiro wrote: It is faster to compare and hash AtomicString than regular Strings. On Fri, May 31, 2013 at 5:57 PM, Brendan Long s...@brendanlong.comwrote: I hope this isn't a stupid question, but I can't find any references to what the difference between AtomicString and String is. It looks like AtomicString is generally preferred, but I don't know why. Can someone fill me in on this? Is there any refences for the classes in WTF? ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev -- Daker Fernandes Pinheiro http://codecereal.blogspot.com ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev -- Rafael Brandao @ INdT ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] When should I use AtomicString vs String?
On Fri, May 31, 2013 at 6:14 PM, Rafael Brandao rafael.l...@openbossa.orgwrote: This thread contains really useful information, so I've created a new topic on https://trac.webkit.org/wiki/EfficientStrings and pointed to here. One thing that always threw me was the term Atomic in the class name. I wonder if the term InternedString would make it usage more apparent. Best regards, Rafael On Fri, May 31, 2013 at 8:32 PM, Ryosuke Niwa rn...@webkit.org wrote: We shouldn't use AtomicString if the string we're about to create doesn't get shared across multiple AtomicStrings. For example, if we had used AtomicString for the strings inside Text nodes, then we may end up filling up the atomic string table with all these really long strings that don't typically appear more than once. It also slows down the hash map look up for all other atomic strings. On Fri, May 31, 2013 at 3:00 PM, Brendan Long s...@brendanlong.comwrote: So should I just never use String and always use AtomicString? On 05/31/2013 03:14 PM, Daker Pinheiro wrote: It is faster to compare and hash AtomicString than regular Strings. On Fri, May 31, 2013 at 5:57 PM, Brendan Long s...@brendanlong.comwrote: I hope this isn't a stupid question, but I can't find any references to what the difference between AtomicString and String is. It looks like AtomicString is generally preferred, but I don't know why. Can someone fill me in on this? Is there any refences for the classes in WTF? ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev -- Daker Fernandes Pinheiro http://codecereal.blogspot.com ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev -- Rafael Brandao @ INdT ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] When should I use AtomicString vs String?
Great! Maybe we even want to add it to http://www.webkit.org/coding/technical-articles.html after converting it to a web page? - R. Niwa On Fri, May 31, 2013 at 5:14 PM, Rafael Brandao rafael.l...@openbossa.orgwrote: This thread contains really useful information, so I've created a new topic on https://trac.webkit.org/wiki/EfficientStrings and pointed to here. Best regards, Rafael On Fri, May 31, 2013 at 8:32 PM, Ryosuke Niwa rn...@webkit.org wrote: We shouldn't use AtomicString if the string we're about to create doesn't get shared across multiple AtomicStrings. For example, if we had used AtomicString for the strings inside Text nodes, then we may end up filling up the atomic string table with all these really long strings that don't typically appear more than once. It also slows down the hash map look up for all other atomic strings. On Fri, May 31, 2013 at 3:00 PM, Brendan Long s...@brendanlong.comwrote: So should I just never use String and always use AtomicString? On 05/31/2013 03:14 PM, Daker Pinheiro wrote: It is faster to compare and hash AtomicString than regular Strings. On Fri, May 31, 2013 at 5:57 PM, Brendan Long s...@brendanlong.comwrote: I hope this isn't a stupid question, but I can't find any references to what the difference between AtomicString and String is. It looks like AtomicString is generally preferred, but I don't know why. Can someone fill me in on this? Is there any refences for the classes in WTF? ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev -- Daker Fernandes Pinheiro http://codecereal.blogspot.com ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev -- Rafael Brandao @ INdT ___ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] When should I use AtomicString vs String?
+1 :-)
On Friday, May 31, 2013, Glenn Adams wrote:
On Fri, May 31, 2013 at 6:14 PM, Rafael Brandao
rafael.l...@openbossa.orgjavascript:_e({}, 'cvml',
'rafael.l...@openbossa.org');
wrote:
This thread contains really useful information, so I've created a new
topic on https://trac.webkit.org/wiki/EfficientStrings and pointed to
here.
One thing that always threw me was the term Atomic in the class name. I
wonder if the term InternedString would make it usage more apparent.
Best regards,
Rafael
On Fri, May 31, 2013 at 8:32 PM, Ryosuke Niwa
rn...@webkit.orgjavascript:_e({}, 'cvml', 'rn...@webkit.org');
wrote:
We shouldn't use AtomicString if the string we're about to create
doesn't get shared across multiple AtomicStrings.
For example, if we had used AtomicString for the strings inside Text
nodes, then we may end up filling up the atomic string table with all these
really long strings that don't typically appear more than once. It also
slows down the hash map look up for all other atomic strings.
On Fri, May 31, 2013 at 3:00 PM, Brendan Long
s...@brendanlong.comjavascript:_e({}, 'cvml', 's...@brendanlong.com');
wrote:
So should I just never use String and always use AtomicString?
On 05/31/2013 03:14 PM, Daker Pinheiro wrote:
It is faster to compare and hash AtomicString than regular Strings.
On Fri, May 31, 2013 at 5:57 PM, Brendan Long
s...@brendanlong.comjavascript:_e({}, 'cvml', 's...@brendanlong.com');
wrote:
I hope this isn't a stupid question, but I can't find any references to
what the difference between AtomicString and String is. It looks like
AtomicString is generally preferred, but I don't know why. Can someone
fill me in on this? Is there any refences for the classes in WTF?
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