On Mon, Sep 5, 2016 at 9:08 PM, Ben Coman <[email protected]> wrote:
> Is it a **requirement** that FFI calls have a method all to themselves
> like a primitive call?
>
> I have this definition...
>
> FFIExternalStructure subclass: #CXString
>
> CXString class>>fieldsDesc
> ^ #(
> void *data;
> uint private_flags;
> )
>
>
> The instance returned by this...
> Xxxx>>getClangVersion
> ^ self ffiCall: #( CXString clang_getClangVersion () ) module:
> Libclang
>
> has private_flags=1 indicating the library allocated external memory
> for *data and to release this I need to call clang_disposeString(
> CXString string). However this doesn't guard against being called
> twice and double-free()'ing CXString crashing the VM, so I defined the
> following...
>
> CXString>>dispose
> self inform: 'debug_dispose1'.
> self private_flags = 1
> ifTrue:
> [ self inform: 'debug_dispose2'.
> self private_flags: 0.
> self ffiCall: #( void clang_disposeString ( CXString
> self ) ) module: Libclang
> ]
> ifFalse:
> [ self inform: 'debug_dispose3'.
> Error signal: 'Cannot dispose twice' ].
>
> However something strange, dispose will only execute once. For example for...
>
> s := Libclang getClangVersion.
> s dispose. "==>debug_dispose1, debug_dispose2"
> s dispose. "==>nothing at all"
>
> I would expect the second call to dispose
> to result it "==>debug_dispose1, debug_dispose3"
> but it does nothing at all. Debugging into "S dispose" displays the
> source of dispose and then returns without executing anything. The
> image seems fine and displays the updated zero in private_flags -- at
> least for a few minutes, then it might crash indicating the
> clang_disposeString() has been called twice.
>
> However it works if I separate out the FFI call to a separate method...
>
> CXString>>unsafeDispose
> self ffiCall: #( void clang_disposeString ( CXString self ) )
> module: Libclang
>
> CXString>>dispose
> self inform: 'dispose1'.
> self private_flags = 1
> ifTrue:
> [ self inform: 'dispose2'.
> self private_flags: 0.
> self unsafeDispose.
> ]
> ifFalse:
> [ self inform: 'dispose3'.
> Error signal: 'Cannot dispose twice' ].
>
> s := Libclang getClangVersion.
> s dispose. "==>debug_dispose1, debug_dispose2"
> s dispose. "==>debug_dispose1, debug_dispose3"
> s dispose. "==>debug_dispose1, debug_dispose3"
> s dispose. "==>debug_dispose1, debug_dispose3"
>
>
> Can someone hazard a guess what is behind this behaviour? I would
> prefer not to require the unguarded #unsafeDispose.
>
> cheers -ben
I'm also trying to understand the FFI memory footprint.
A freshly started image uses this memory (kb)...
VIRT RES SHR
118132 108644 5920
Creation and GC of the FFIExternalStructure is no problem...
all := OrderedCollection new.
10 000 000 timesRepeat: [ all add: CXString new. ].
all := nil.
Smalltalk garbageCollect.
VIRT RES SHR
122,268 115,244 5,788
And performing the FFI calls is not too bad (particularly that
repeating this doesn't grow memory further)...
10 000 000 timesRepeat: [ Libclang getClangVersion unsafeDispose ].
Smalltalk garbageCollect.
VIRT RES SHR
170,404 123,252 12,084
But combining those two...
all := OrderedCollection new.
1000000 timesRepeat: [ all add: Libclang getClangVersion ].
all do: [ :s | s unsafeDispose. ].
all := nil.
Smalltalk garbageCollect.
CXString allInstances size "==> 0".
increases memory considerably...
VIRT RES SHR
1,029,836 982,336 11,740
But again, repeating that a dozen times doesn't grow memory further.
Save/quiting the image and reopening it returns to original memory usage...
VIRT RES SHR
118,132 108,620 5,896
.
So I'm curious what might be holding onto the memory.
cheers -ben
P.S. a bit more background info on the library...
extern "C" {
CXString clang_getClangVersion() {
return cxstring::createDup(getClangFullVersion());
}
} //
https://github.com/llvm-mirror/clang/blob/google/stable/tools/libclang/CIndex.cpp
CXString createDup(const char *String) {
if (!String)
return createNull();
if (String[0] == '\0')
return createEmpty();
CXString Str;
Str.data = strdup(String);
Str.private_flags = CXS_Malloc;
return Str;
}
void clang_disposeString(CXString string) {
switch ((CXStringFlag) string.private_flags) {
case CXS_Unmanaged:
break;
case CXS_Malloc:
if (string.data)
free(const_cast<void *>(string.data));
break;
case CXS_StringBuf:
static_cast<cxstring::CXStringBuf *>(
const_cast<void *>(string.data))->dispose();
break;
}
}
