On Thu, May 7, 2015 at 8:53 AM, Holger Freyther <holger@freyther.de> wrote:

Good Morning,

I used NB to access openlog, closelog and syslog of libc and I am not sure if I got it right but didn’t really get further by browsing testcases/reading the examples.

openlog(3) takes an “char *ident” as first parameter and the caller needs to make sure that the string passed remains valid until closelog is called.

My binding looks like this:

c_openlog: ident opt: aOpt facility: aFac "openlog(const char *ident, int logopt, int facility);" <primitive: #primitiveNativeCall module: #NativeBoostPlugin error: errorCode> ^self nbCall: #(void openlog(char *ident, int aOpt, int aFac))

And I call it like this:

Identity := anIdentity asNBExternalString. self c_openlog: Identity opt: anOption facility: aFacility.

The things I am not sure with:

1.) is it right to use “char *ident” instead of “String ident”? “String” will copy the string by value but the pointer passed to openlog would be a pointer from the C callstack?

asNBExternalString will do this with a NBExternalAddress: fromString: aString | result | result := NativeBoost allocate: aString size + 1. (self assert: result notNil). result writeString: aString. ^ result writeString: aString "write a null-terminated byte string to receiver's address" | str | str := aString copyWith: (Character value: 0). NativeBoost memCopy: str asByteArray to: self size: str size. So, yes, it allocates heap memory basicAllocate: numBytes "Allocate a memory block with given size in bytes, answer an NBExternalAddress instance - address to the beginning of memory block" | addr | addr := heap allocate: numBytes. addr = 0 ifTrue: [ ^ nil ]. ^ NBExternalAddress value: addr char * looks a null terminated string, which str := aString copyWith: (Character value: 0). provides So, asNBExternalString is compatible with the char *

2.) Am I right with the call to asNBExternalString?

Should work.

3.) How does this integrate with GC and image quit/image resume? E.g. I could use >>#freeAfterUse and if I do “Identity := nil” at some point free should be called on the old string. Is there anything in the system that sets the address to 0x0 after the image is starting?

As the thing is a NBExternalAddress, there is a finalize self free which will do the "free" call when the Identity will be gc'd. As for the statup/shutdown, maybe startUp: resuming shutDown: quitting methods on the class side of your facility will do the necessary things. I am pretty sure the address would be pointing to invalid crap upon image restart. Doing free too many times will just raise an error I guess (which you can catch). free: address sema critical: [ | block | block := reservedBlocks removeKey: address ifAbsent: [ self error: 'Unable to find a memory block with given address' ]. block makeFreeFor: self ] HTH Phil

thanks holger