[Rd] Return a list from a .Call but segfaults

[Saptarshi Guha]

After some examination, this is what i found (i changed the code
somewhat, i dont modify rawdata anymore)

load("/tmp/v.Rdata")
dyn.load("/ln/meraki/custom/lib64/R/library/mylib/libs/lib.so")
v=.Call("returnListOfKV",rawkv,numread)

## v is a list of 28231 lists each of length 2
j=v[1:10000] ; u=list();u=append(u,j)
and
 j=v[1:15164] ; u=list();u=append(u,j)
both work but for n> 15164
 j=v[1:n] ; u=list();u=append(u,j)
returns
Error: protect(): protection stack overflow

I have no idea why...
Regards
Saptarshi




On Sat, Sep 19, 2009 at 10:15 PM, Saptarshi Guha
<saptarshi.guha at gmail.com> wrote:
> Hello,
> I call a function via .Call passing to it a raw vector(D) and an integer(I)
> The vector is a series  K1,KData1, V1,VData1, K2, KData2, ...
> where the integer K1 is the length of Data1 and similarly for Ki (wrt
> Datai)(similarly for V*) There 2*I such pairs( (Ki,KDatai), (Vi,VDatai))
>
> The numbers Ki(and Vi) are written in network order.
>
> I am returning a list of I elements each element a list of two elements
> corresponding to KData and VData (which are serialized R objects) .
>
>  ll <- .Call("returnListOfKV", rawkv, numread)
>
> When use the function with browser(), and type head(ll) i get valid results.
> However, i get a segfault when the code runs the next line
>
>  j <- append(j,ll)
>
> (where j was defined as vector(mode='list') )
>
> The code below looks alright, but it appears to crash when getting copied.
> Now one could blame message2rexp (in kk_), but once in R, the result of
> .Call is assigned to ll, everything should be protected.
> In fact, if in kk_ i simply return a VECSXP with 2 elements, no errors, so
> one could conclude that message2rexp is to blame.
>
> Yet, when i replace the code with R code, that is using readBin and only
> calling calling C(to call message2rexp) to deserialize a raw vector, I get
> no such error.
>
> There is something I'm missing , could someone tell me where?
> Thank you for your time
> Regards
> Saptarshi
>
>
> === Using GDB? ====
> I would like to run it through gdb, i get the following message
> [Thread debugging using libthread_db enabled]
> Error while reading shared library symbols:
> Cannot find new threads: generic error
> Cannot find new threads: generic error]
>
> and cannot proceed.
>
> ==== Code ====
>  SEXP returnListOfKV(SEXP raw,SEXP numread){
>
>    if(TYPEOF(raw)!=RAWSXP){
>      return(R_NilValue);
>    }
>    int num = INTEGER(numread)[0];
>    char *rawdata = (char*)RAW(raw);
>    SEXP KV ,rval;
>    int r;
>    PROTECT(rval = Rf_allocVector(VECSXP, num));
>    for(int i=0;i<num;i++){
>      SEXP k = R_NilValue;
>      PROTECT(KV = Rf_allocVector(VECSXP, 2));
>
>      r = reverseUInt(*((int*) rawdata)); //converts network order to host
>      rawdata+=4; //yes, hard code size of int
>      PROTECT(k= kk_(rawdata,r)); //deserializes data and returns a SEXP
>      rawdata+= r;
>      SET_VECTOR_ELT(KV,0, k);
>      UNPROTECT(1);
>
>      r = reverseUInt(*((int*) rawdata));
>      rawdata+=4;
>      PROTECT(k= kk_(rawdata,r));
>      rawdata+=r;
>      SET_VECTOR_ELT(KV,1, k);
>      UNPROTECT(1);
>
>      SET_VECTOR_ELT(rval,i,KV);
>      UNPROTECT(1);
>    }
>    UNPROTECT(1);
>    return(rval);
>  }
>
>
>  SEXP kk_(char *d,int n){
>    SEXP k;
>    REXP *rexp = new REXP();
>    rexp->Clear();
>    rexp->ParseFromArray(d,n);
>    PROTECT(k = message2rexp(*rexp));
>    delete(rexp);
>    UNPROTECT(1);
>    return(k);
>  }
>
> Saptarshi Guha | saptarshi.guha at gmail.com |
> http://www.stat.purdue.edu/~sguha
>
>
>