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Private method wrapping eliminated

This has wonderful consequences; see branch commits for more information.
perfodd
Mike Gerwitz 2014-03-20 23:55:27 -04:00
commit 9c70904c39
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4 changed files with 114 additions and 3 deletions

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@ -1469,6 +1469,65 @@ constructor logic and replacing methods at runtime. This is useful for
mocking, but a complete anti-pattern in terms of Classical Object-Oriented mocking, but a complete anti-pattern in terms of Classical Object-Oriented
development.} development.}
@subsubsection Private Method Performance
A special exception to GNU ease.js' method wrapping implementation is made
for private methods. As mentioned above, there are a number of downsides to
method wrapping, including effectively halving the remaining stack space for
heavily recursive operations, overhead of closure invocation, and thwarting
of tail call optimization. This situation is rather awkward, because it
essentially tells users that ease.js should not be used for
performance-critical invocations or heavily recursive algorithms, which is
very inconvenient and unintuitive.
To eliminate this issue for the bulk of program logic, method wrapping does
not occur on private methods. To see why it is not necessary, consider the
purpose of the wrappers:
@enumerate
@item
All wrappers perform a context lookup, binding to the instance's private
visibility object of the class that defined that particular method.
@item
This context is restored upon returning from the call: if a method returns
@var{this}, it is instead converted back to the context in which the method
was invoked, which prevents the private member object from leaking out of a
public interface.
@item
In the event of an override, @var{this.__super} is set up (and torn down).
@end enumerate
There are other details (e.g. the method wrapper used for @ref{Method
Proxies,,method proxies}), but for the sake of this particular discussion,
those are the only ones that really matter. Now, there are a couple of
important details to consider about private members:
@itemize
@item
Private members are only ever accessible from within the context of the
private member object, which is always the context when executing a method.
@item
Private methods cannot be overridden, as they cannot be inherited.
@end itemize
Consequently:
@enumerate
@item
We do not need to perform a context lookup: we are already in the proper
context.
@item
We do not need to restore the context, as we never needed to change it to
begin with.
@item
@var{this.__self} is never applicable.
@end enumerate
This is all the more motivation to use private members, which enforces
encapsulation; keep in mind that, because use of private members is the
ideal in well-encapsulated and well-factored code, ease.js has been designed
to perform best under those circumstances.
@node Pre-ES5 Fallback @node Pre-ES5 Fallback
@subsection Pre-ES5 Fallback @subsection Pre-ES5 Fallback
For any system that is to remain functionally compatible across a number of For any system that is to remain functionally compatible across a number of

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@ -337,6 +337,10 @@ method}, with the name @var{_moveFrontLeg}. The old method will still be
called. Instead, we would have to override the public @var{walk} method to called. Instead, we would have to override the public @var{walk} method to
prevent our dog from moving his front feet. prevent our dog from moving his front feet.
Note that GNU ease.js is optimized for private member access; see
@ref{Property Proxies,,Property Proxies} and @ref{Method
Wrapping,,Method Wrapping} for additional details.
@subsection Protected Members @subsection Protected Members
Protected members are often misunderstood. Many developers will declare all Protected members are often misunderstood. Many developers will declare all
of their members as either public or protected under the misconception that of their members as either public or protected under the misconception that

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@ -173,9 +173,12 @@ exports.buildMethod = function(
} }
} }
else if ( keywords[ 'abstract' ] ) else if ( keywords[ 'abstract' ] || keywords[ 'private' ] )
{ {
// we do not want to wrap abstract methods, since they are not callable // we do not want to wrap abstract methods, since they are not
// callable; further, we do not need to wrap private methods, since
// they are only ever accessible when we are already within a
// private context (see test case for more information)
dest[ name ] = value; dest[ name ] = value;
} }
else else

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@ -67,7 +67,11 @@ require( 'common' ).testCase(
// stub factories used for testing // stub factories used for testing
var stubFactory = this.require( 'MethodWrapperFactory' )( var stubFactory = this.require( 'MethodWrapperFactory' )(
function( func ) { return func; } function( func )
{
// still wrap it so that the function is encapsulated
return function() { return func() };
}
); );
// used for testing proxies explicitly // used for testing proxies explicitly
@ -282,4 +286,45 @@ require( 'common' ).testCase(
this.members[ 'public' ].foo(); this.members[ 'public' ].foo();
this.assertOk( called, "Override unkept" ); this.assertOk( called, "Override unkept" );
}, },
/**
* This is a beautiful consequence of the necessay context in which
* private methods must be invoked.
*
* If a method has the ability to call a private method, then we must
* already be within a private context (that is---using the private
* member object, which happens whenever we're executing a method of
* that class). The purpose of the method wrapper is to (a) determine
* the proper context, (b) set up super method references, and (c)
* restore the context in the event that the method returns `this'. Not
* a single one of these applies: (a) is void beacuse we are already in
* the proper context; (b) is not applicable since private methods
* cannot have a super method; and (c) we do not need to restore context
* before returning because the context would be the same (per (a)).
*
* That has excellent performance implications: not only do we reduce
* class building times for private methods, but we also improve method
* invocation times, since we do not have to invoke a *closure* for each
* and every method call. Further, recursive private methods are no
* longer an issue since they do not gobble up the stack faster and,
* consequently, the JavaScript engine can now take advantage of tail
* call optimizations.
*
* This is also further encouragement to use private members. :)
*/
'Private methods are not wrapped': function()
{
var f = function() {},
name = 'foo';
this.sut.buildMethod(
this.members, {}, name, f, { 'private': true },
function() {}, 1, {}
);
// if the private method was not wrapped, then it should have been
// assigned to the member object unencapsulated
this.assertStrictEqual( this.members[ 'private' ][ name ], f );
},
} ); } );