Very nice topic coverage. I hope, eventually NB will also have
something like this :)
But it having a little different pros/cons table:
NB Pros:
* as well as for plugin, you can create new
functionality that doesn't exist in any library
* no need to recompile plugin/VM when you making a changes
* all your code is distributed with the Smalltalk code,
but there can be
complications with platforms
* fast - faster than any FFI implementation written in
C, and as fast as plugin primitive or even faster
Cons:
* ?unsafe? - you have to provide a safety layers
(But hey, you have to deal with same sorts of stuff,
when writing plugin. No magician workers there)
* harder to write
Yes, its harder than plain smalltalk - true.
But i can't say, that writing an assembler is harder than writing a
plugin's slang code.
If you writing a plugin, you should have an expertise, in VM internals
and how to build VM , etc etc
and if you writing an native code, you should have an expertise in
assembler as well as VM internals.
So, they are different, and definitely much harder comparing to plain
smalltalk code,
but which one is easier is hard to tell.
On 20 May 2010 22:25, Stéphane Ducasse <[email protected]> wrote:
> thanks sean
> this is cool to see such kind of documentation emerging.
>
> Stef
>
> On May 20, 2010, at 9:16 PM, Sean P. DeNigris wrote:
>
>>
>> I want to get this info into the help system and/or collaborative book, as
>> similar questions pop up regularly on the lists.
>>
>> I compiled every piece of info I could find. The focus in on FFI, with
>> stubs for other strategies. Please read this *very* rough outline for
>> missing info and inaccuracies:
>>
>> FFI
>>
>> What is FFI and what is it used for? Calling functions in libraries outside
>> of the image...
>>
>> FFI, the Squeak Foreign Function Interface, is used to call functions
>> located in shared libraries that are not part of the Squeak VM nor its
>> plugins. It also provides means to read and write memory structures that are
>> associated with the use of those shared libraries. A typical use is to
>> directly invoke operating system APIs. As such, applications that use FFI
>> can only be used on the platform(s) that support the particular API being
>> used. C conventions are used throughout, though the external function could
>> have been written by any language capable of generating object code that
>> follows C conventions. FFI is probably the easiest way to do the things it
>> does. FFI is pretty fast too. Croquet uses FFI calls to OpenGL for all it's
>> drawing routines.[1]
>>
>> How does FFI work?
>> Technically what happens is:
>> * you define what the interface is - the parameters, types etc.
>> * when you make the call, the FFI logic assembles the data from the Squeak
>> Objects into the proper structures according to the routine calling
>> conventions for your architecture, and of course manages the return values.
>> So no magic but perhaps just a little assembler in the plugin to properly
>> deal with all the registers and condition flags.
>>
>> How do I use it?
>>
>> 1. make a method (whose structure is similar to a named primitive method)
>>
>> Example:
>> system: aString "name (by convention is apiXxx: e.g. apiSystem:)"
>>
>> <apicall: long 'system' (char*) module: 'libSystem.dylib'> "first line
>> should be the external function specification"
>> ^self externalCallFailed.
>>
>> Let's take it piece by piece:
>>
>> system: aString
>> Method name - by convention named 'apiXxx'
>>
>> <apicall: long 'system' (char*) module: 'libSystem.dylib'>
>> Function specification
>> - should be the first line
>> - enclosed in angle brackets: < > containing:
>> 1. Calling Convention, either apicall: (Pascal
>> convention) or cdecl: (C
>> convention)
>> - Mac - use either one
>> - Unix - use cdecl
>> - Windows - use apical
>> 2. Return Type (see types)
>> 3. External Function Name (literal string)
>> 4. Argument Types (a literal array)
>> 5. Module - "module: " + [filename of the
>> external library (literal
>> string)] (see below).
>>
>> self externalCallFailed.
>> Failure handler
>> - normal smalltalk code
>> - executed if the linking to or calling the external
>> function fails
>> - API calls don't know how to communicate failure like
>> Squeak primitives
>> do, so:
>> - it does not tell you whether the external
>> function succeeded
>> - the most common code is simply '^self
>> externalCallFailed.'
>>
>> Argument Types
>> - must be names of ExternalTypes, either:
>> - atomic types (see ExternalType class>>initializeFFIConstants
>> and
>> ExternalType class>>initializeAtomicTypes):
>> void
>> bool
>> byte (unsigned)
>> sbyte (signed)
>> ushort (16-bit unsigned)
>> short (16-bit signed)
>> ulong (32-bit unsigned)
>> long (32-bit signed)
>> ulonglong (64-bit unsigned)
>> longlong (64-bit signed)
>> char (unsigned)
>> schar (signed)
>> float (single-precision float)
>> double (double-precision float)
>>
>> Structure Types [4]
>> - subclass of ExternalStructure
>> - class>>fields that returns an array of field descriptions
>> (see below)
>> - Example:
>> fields
>> ^#((red 'byte')(green 'byte')(blue
>> 'byte'))
>> - class>>initialize which includes "self defineFields" (which
>> must be
>> called before using the class)
>> - refer to as MyExternalStructure* (to indicate that the argument or
>> return
>> is a pointer to that structure)
>>
>> Field description [4]
>> - 2-element array (or three but that does something else, I'm not sure
>> what):
>> - first element is the field name
>> - second is the type
>>
>> Mac Memory Allocation Issues [4] (not sure about this)
>>
>> If you allocate external structures, those with memory outside the Squeak
>> process space, you may need to increase the amount of memory that is
>> reserved outside the object heap for such use. The Mac OS (9 and previous)
>> needs this, other platforms may be able to dynamically get more memory from
>> the OS. To see how much memory is currently reserved printIt 'Smalltalk
>> extraVMMemory'. To change it, execute 'Smalltalk extraVMMemory:
>> someNumberofBytes' Then save your image and quit. When you next start up,
>> the amount of memory you requested will be reserved. (JMM) Note the OSX
>> versions of the VM ignore extraVMMemory because the memory model for
>> OS-X/unix applications is quite different.
>>
>> Module Name
>> - depends on the platform
>> - Mac
>> - pre Snow Leopard: flexible, can eliminate leading lib or
>> extension e.g.
>> 'libc.dylib' becomes 'libc', 'c.dylib', or 'c'
>> - Snow Leopard
>> - file name must be exact including extension (unless
>> Info.plist is
>> altered as in 'Library Location' below)
>> - With pre-mach-o VMs
>> - For Classic applications, use 'InterfaceLib'
>> - For Carbon libs, use 'CarbonLib'
>>
>> Module Location - where the external library file lives
>> - depends on the platform
>> - Mac
>> - pre Snow Leopard
>> - checks VM path and common library paths
>> - Snow Leopard
>> - only looks in VM bundle's Resources file,
>> you must either [5]:
>> - store all external libraries there
>> - ln -s path/to/library
>> path/to/VM/Resources/library_name
>> - Change the VM's Info.plist
>> "SqueakPluginsBuiltInOrLocalOnly" key from
>> "true" to "false."
>> Caveats
>> - security
>> - malicious users could call arbitrary functions in the OS
>> e.g. "format
>> c:" from "system.dll" [7]
>> - VMs do not protect against buffer overflow from bad
>> parameters [8]:
>> "this would require an attacker to execute arbitrary
>> Smalltalk
>> code on your server. Of course if they can do that
>> they own you
>> anyway, especially if you allow FFi or use the
>> OSProcess plugin" - John
>> McIntosh
>>
>> * difficulty
>> - if you make a mistake you'll not drop into the debugger but Squeak
>> will
>> just crash [2]
>> - If you crash Squeak when it is running the garbage collector, then
>> you
>> know your FFI code is leaking bits into object memory [2]
>>
>> What do I need to use FFI with Squeak?
>>
>> You need the FFI plugin, which is included with most VM's as of Squeak 3.6
>> or so.
>>
>> You can also build the plugin yourself. See VMMaker.
>>
>> References:
>> [1] http://wiki.squeak.org/squeak/1414
>> [2] http://wiki.squeak.org/squeak/2424
>> [3] http://wiki.squeak.org/squeak/5716
>> [4] http://wiki.squeak.org/squeak/2426
>> [5]
>> http://forum.world.st/squeak-dev-Alien-Squeak-FFI-issues-on-Snow-Leopard-td85608.html
>> [6] http://wiki.squeak.org/squeak/5846
>> [7] http://forum.world.st/FFI-Callbacks-td54056.html#a54073
>> [8] http://forum.world.st/Security-td99624.html#a99635:
>>
>> Other choices:
>> In the fall of 2008, Alien the FFI interface (written by Cadence Design
>> Systems, Inc.) was put into squeaksource:
>> http://www.squeaksource.com/Alien.html. This API allows the primitive to
>> call back to Smalltalk Code, and return error code information, and
>> apparently is much faster due to a less complex call sequence.
>> * if you need callbacks
>> * mac-only?
>>
>> Plugins - write external code and dynamically link it to the VM
>> Pros:
>> * safest - users are limited to using the functionality you
>> provide and
>> can not call other external functions e.g. system rm /
>> * fast - faster than FFI
>> * you can create new functionality that doesn't exist in any
>> library
>> Cons:
>> * harder to write
>> * plugin must be distributed with the Smalltalk code - there
>> can be
>> complications with platforms
>>
>> Primitive method - invokes behavior in the VM or a plugin [3]
>>
>> Questions:
>> * why would you want to build the FFI plugin yourself?
>> * api prefix or no for method names?
>> * not sure about pre Snow Leopard library search
>> * OSProcess - how does this fit into the bigger picture?
>> * "^self externalCallFailed." or "self externalCallFailed." i.e. return self
>> or return the result, or doesn't matter?
>> * why would a field description have three elements?
>> * Mac Memory Allocation Issues?
>> --
>> View this message in context:
>> http://forum.world.st/FFI-Documentation-tp2225148p2225148.html
>> Sent from the Pharo Smalltalk mailing list archive at Nabble.com.
>>
>> _______________________________________________
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>> [email protected]
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>
>
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--
Best regards,
Igor Stasenko AKA sig.
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