Re: [webkit-dev] Hash tables and unique string identifiers in JavaScriptCore
On Wed, Sep 19, 2012 at 1:32 AM, Geoffrey Garen gga...@apple.com wrote: Thanks! So is PropertyMapHashTable for properties that have been defined by the user, or is it not that simple? Yes. Apologies. Basically, does the implementation of object property access in the JIT codebase also use strings which have been made unique identifiers in the same way as in the runtime stack? (i.e. can they be assumed equal iff they have the same address). Yes -- typically, though, if the JIT needs to do a hash lookup, it will pass an Identifier to a C++ helper function. Thanks! Do you mind pointing me to where this happens in the code? (passing an Identifer to a C++ helper?) Geoff Stephen ___ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] Hash tables and unique string identifiers in JavaScriptCore
Thanks! Do you mind pointing me to where this happens in the code? (passing
an Identifer to a C++ helper?)
Here's an example function called by the JIT, from DFGOperations.cpp:
void DFG_OPERATION operationPutByIdNonStrict(ExecState* exec, EncodedJSValue
encodedValue, JSCell* base, Identifier* propertyName)
{
JSGlobalData* globalData = exec-globalData();
NativeCallFrameTracer tracer(globalData, exec);
PutPropertySlot slot(false);
base-methodTable()-put(base, exec, *propertyName,
JSValue::decode(encodedValue), slot);
}
Geoff
___
webkit-dev mailing list
webkit-dev@lists.webkit.org
http://lists.webkit.org/mailman/listinfo/webkit-dev
[webkit-dev] Hash tables and unique string identifiers in JavaScriptCore
Hi, I just started working with webkit (specificially JSC) and am trying to learn the codebase. I hope someone can bear with me enough to help me with some questions: 1. I notice there are at least two implementations of hash tables in JavaScriptCore/runtime, in Lookup.h and PropertyMapHashTable.h. Which, if either, is used in, say, the normal case of accessing the properties of a DOM element, like window.location, etc.? And assuming it's one or the other, what's the main use case of the other one? 2. Also, it looks like string keys in Lookup.h are always Identifiers, meaning (I think) that they are guaranteed to be single unique entries in the identifierTable of a JSGlobalData object. Because of this preprocessing, string equality in the hash table implementation can be tested just by comparing addresses. Is there any reason why PropertyMapHashTable.h does not (as far as I can tell) do the same thing? 3. Does the JIT side of the codebase use unique string identifiers like Lookup.h does, or is that a whole different ballgame? Thanks very much in advance for help! Stephen ___ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] Hash tables and unique string identifiers in JavaScriptCore
Hi Stephen.
1. I notice there are at least two implementations of hash tables in
JavaScriptCore/runtime, in Lookup.h and PropertyMapHashTable.h. Which, if
either, is used in, say, the normal case of accessing the properties of a DOM
element, like window.location, etc.? And assuming it's one or the other,
what's the main use case of the other one?
window.location uses Lookup.h. Lookup.h contains hash table logic for static
properties compiled into the binary.
2. Also, it looks like string keys in Lookup.h are always Identifiers,
meaning (I think) that they are guaranteed to be single unique entries in the
identifierTable of a JSGlobalData object. Because of this preprocessing,
string equality in the hash table implementation can be tested just by
comparing addresses. Is there any reason why PropertyMapHashTable.h does not
(as far as I can tell) do the same thing?
It does.
inline PropertyTable::find_iterator PropertyTable::find(const KeyType key)
{
ASSERT(key);
ASSERT(key-isIdentifier() || key-isEmptyUnique());
unsigned hash = key-existingHash();
3. Does the JIT side of the codebase use unique string identifiers like
Lookup.h does, or is that a whole different ballgame?
Can you be more specific?
Geoff
___
webkit-dev mailing list
webkit-dev@lists.webkit.org
http://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] Hash tables and unique string identifiers in JavaScriptCore
On Wed, Sep 19, 2012 at 1:12 AM, Geoffrey Garen gga...@apple.com wrote:
Hi Stephen.
1. I notice there are at least two implementations of hash tables in
JavaScriptCore/runtime, in Lookup.h and PropertyMapHashTable.h. Which, if
either, is used in, say, the normal case of accessing the properties of a
DOM element, like window.location, etc.? And assuming it's one or the
other, what's the main use case of the other one?
window.location uses Lookup.h. Lookup.h contains hash table logic for
static properties compiled into the binary.
Thanks! So is PropertyMapHashTable for properties that have been defined by
the user, or is it not that simple?
2. Also, it looks like string keys in Lookup.h are always Identifiers,
meaning (I think) that they are guaranteed to be single unique entries in
the identifierTable of a JSGlobalData object. Because of this
preprocessing, string equality in the hash table implementation can be
tested just by comparing addresses. Is there any reason why
PropertyMapHashTable.h does not (as far as I can tell) do the same thing?
It does.
inline PropertyTable::find_iterator PropertyTable::find(const KeyType key)
{
ASSERT(key);
ASSERT(key-isIdentifier() || key-isEmptyUnique());
unsigned hash = key-existingHash();
My mistake: the second assert seems to not be there in QtWebKit-2.2.0, the
version I'm looking through, but I reading further I realized that keys are
also assumed to be unique identifiers with the comparison below.
if (key == table()[entryIndex - 1].key)
return std::make_pair(table()[entryIndex - 1], hash
m_indexMask);
(The way the types resolve, the key comparison is done on address rather
than value, as I assumed the first time I read it)
3. Does the JIT side of the codebase use unique string identifiers like
Lookup.h does, or is that a whole different ballgame?
Can you be more specific?
Apologies. Basically, does the implementation of object property access in
the JIT codebase also use strings which have been made unique identifiers
in the same way as in the runtime stack? (i.e. can they be assumed equal
iff they have the same address). I can't seem to find any code that does
it, but I am new to the whole tree.
Geoff
Thanks!
___
webkit-dev mailing list
webkit-dev@lists.webkit.org
http://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] Hash tables and unique string identifiers in JavaScriptCore
Thanks! So is PropertyMapHashTable for properties that have been defined by the user, or is it not that simple? Yes. Apologies. Basically, does the implementation of object property access in the JIT codebase also use strings which have been made unique identifiers in the same way as in the runtime stack? (i.e. can they be assumed equal iff they have the same address). Yes -- typically, though, if the JIT needs to do a hash lookup, it will pass an Identifier to a C++ helper function. Geoff ___ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo/webkit-dev
