vcat StackOverflowError in julia - julia

Question

I have written a function to detect objects in arrays. In this case I use it to clear white objects, which touch the border of an image. But the problem is, that there is always a StackOverFlowError in vcat and it occurs at different lines (depends on image). Here is a minimum working example. It works fine with the second image, but not with the first:
using Images
function getImChars(I::Array)
charAr=copy(I);
indexMax=find(x->(x==1),charAr);
(h,w)=size(charAr);
# check border values
(r,c)=ind2sub(size(charAr),indexMax);
indexBorderR1=find(x->(x==1),r);
indexBorderR2=find(x->(x==h),r);
indexBorderR=[indexBorderR1;indexBorderR2];
indexBorderC1=find(x->(x==1),c);
indexBorderC2=find(x->(x==w),c);
indexBorderC=[indexBorderC1;indexBorderC2];
borderPixels=[999;999]; # initialize def value FIX
for bRc=1:length(indexBorderR)
borderPixels=[borderPixels [r[indexBorderR[bRc]];c[indexBorderR[bRc]]]];
end
for bCc=1:length(indexBorderC)
borderPixels=[borderPixels [r[indexBorderC[bCc]];c[indexBorderC[bCc]]]];
end
borderPixels=borderPixels[:,2:end];
(rbP,cbP)=size(borderPixels);
fcharAr=[];
for k=1:cbP
bP=[borderPixels[:,k];false;false;false;false];
locObj1=[];
locObj2=[];
locObj3=[];
locObj4=[];
locObj5=[];
locObj6=[];
if(charAr[bP[1],bP[2]]==0)
continue;
else
charAr[bP[1],bP[2]]=0;
end
recGetCharClearBorders(true,false,h,w,bP,locObj1,locObj2,locObj3,locObj4,locObj5,locObj6,charAr);
end
return charAr;
end
function recGetCharClearBorders(firstFlag::Bool,doNotAdd::Bool,h::Int,w::Int,hP::Array,locObj1::Array,locObj2::Array,locObj3::Array,locObj4::Array,locObj5::Array,locObj6::Array,imAr::Array)
leftPoint=[hP[1];hP[2]-1;0;0;0;0];
rightPoint=[hP[1];hP[2]+1;0;0;0;0];
topPoint=[hP[1]-1;hP[2];0;0;0;0];
bottomPoint=[hP[1]+1;hP[2];0;0;0;0];
# check if it is not out of bounds and relative directions
if(topPoint[1]!=0)
if(imAr[topPoint[1],topPoint[2]]==1)
hP[4]=1;
end
end
if(bottomPoint[1]!=(h+1))
if(imAr[bottomPoint[1],bottomPoint[2]]==1)
hP[6]=1;
end
end
if(leftPoint[2]!=0)
if(imAr[leftPoint[1],leftPoint[2]]==1)
hP[3]=1;
end
end
if(rightPoint[2]!=(w+1))
if(imAr[rightPoint[1],rightPoint[2]]==1)
hP[5]=1;
end
end
# add first elements
if(firstFlag)
locObj1=collect(hP[1]);
locObj2=collect(hP[2]);
locObj3=collect(hP[3]);
locObj4=collect(hP[4]);
locObj5=collect(hP[5]);
locObj6=collect(hP[6]);
firstFlag=false;
else
# if first element of locObj was deleted actual point should not get pushed to array
if(!doNotAdd)
push!(locObj1,hP[1]);
push!(locObj2,hP[2]);
push!(locObj3,hP[3]);
push!(locObj4,hP[4]);
push!(locObj5,hP[5]);
push!(locObj6,hP[6]);
imAr[hP[1],hP[2]]=0;
end
end
goL=false;
goT=false;
goR=false;
goB=false;
doNotAdd=false;
if(length(locObj1)!=0)
# always take and check first elements of locObj
hPfInLoc=[locObj1[1],locObj2[1],locObj3[1],locObj4[1],locObj5[1],locObj6[1]];
hPl=[hPfInLoc[1];hPfInLoc[2]-1;0;0;0;0];
hPt=[hPfInLoc[1]-1;hPfInLoc[2];0;0;0;0];
hPr=[hPfInLoc[1];hPfInLoc[2]+1;0;0;0;0];
hPb=[hPfInLoc[1]+1;hPfInLoc[2];0;0;0;0];
compL=false;
compT=false;
compR=false;
compB=false;
# check bounds and if array values have changed
if(hPt[1]!=0)
if(imAr[hPt[1],hPt[2]]!=0)
compT=true;
end
end
if(hPb[1]!=(h+1))
if(imAr[hPb[1],hPb[2]]!=0)
compB=true;
end
end
if(hPl[2]!=0)
if(imAr[hPl[1],hPl[2]]!=0)
compL=true;
end
end
if(hPr[2]!=(w+1))
if(imAr[hPr[1],hPr[2]]!=0)
compR=true;
end
end
# define directions and set defined direction false in locObj
if((locObj3[1]==1)& compL)
locObj3[1]=0;
goL=true;
elseif((locObj4[1]==1)& compT)
locObj4[1]=0;
goT=true;
elseif((locObj5[1]==1)& compR)
locObj5[1]=0;
goR=true;
elseif((locObj6[1]==1)& compB)
locObj6[1]=0;
goB=true;
else
if (length(locObj1)==1)
locObj=[];
else # if everything is zero delete first rows of arrays
deleteat!(locObj1,1);
deleteat!(locObj2,1);
deleteat!(locObj3,1);
deleteat!(locObj4,1);
deleteat!(locObj5,1);
deleteat!(locObj6,1);
doNotAdd=true;
return recGetCharClearBorders(firstFlag,doNotAdd,h,w,hP,locObj1,locObj2,locObj3,locObj4,locObj5,locObj6,imAr);
end
end
end
#execute choosen direction
if(goL)
return recGetCharClearBorders(firstFlag,doNotAdd,h,w,hPl,locObj1,locObj2,locObj3,locObj4,locObj5,locObj6,imAr);
end
if(goT)
return recGetCharClearBorders(firstFlag,doNotAdd,h,w,hPt,locObj1,locObj2,locObj3,locObj4,locObj5,locObj6,imAr);
end
if(goR)
return recGetCharClearBorders(firstFlag,doNotAdd,h,w,hPr,locObj1,locObj2,locObj3,locObj4,locObj5,locObj6,imAr);
end
if(goB)
return recGetCharClearBorders(firstFlag,doNotAdd,h,w,hPb,locObj1,locObj2,locObj3,locObj4,locObj5,locObj6,imAr);
end
end
# execute test procedure
Im=Images.load("Test.png");
Im=data(Im);
imAr=map(Float64,Im);
resIm=getImChars(imAr);
save("Imout.png",resIm);
You only have to change the name of the image in my code. Just tell me, if you need some more information. Thanks a lot.
Cheers, clax

Answer 1

Unlike many functional programming language, Julia doesn't optimize for tail recursion (reusing the stack frame when a function ends by a call). So in your case it is very likely that your recursive function hits the max stack depths depending on your OS's thread stack size.
Unfortunately, the Julia core team decide not to prioritise Tail call optimization as they don't deem such feature a must. Indeed people can often refactor their code into loops.
Afaik, tail call optimization is pretty difficult and many other programming languages featuring functional programming paradigm also lack it.

Answer 2

Took a few minutes needed to run and fixup the tail recursion. Is the following replacement for recGetCharClearBorders performing correctly:
function recGetCharClearBorders(firstFlag::Bool,doNotAdd::Bool,h::Int,w::Int,hP::Array,locObj1::Array,locObj2::Array,locObj3::Array,locObj4::Array,locObj5::Array,locObj6::Array,imAr::Array,recdepth,recloc)
while true
leftPoint=[hP[1];hP[2]-1;0;0;0;0];
rightPoint=[hP[1];hP[2]+1;0;0;0;0];
topPoint=[hP[1]-1;hP[2];0;0;0;0];
bottomPoint=[hP[1]+1;hP[2];0;0;0;0];
# check if it is not out of bounds and relative directions
if(topPoint[1]!=0)
if(imAr[topPoint[1],topPoint[2]]==1)
hP[4]=1;
end
end
if(bottomPoint[1]!=(h+1))
if(imAr[bottomPoint[1],bottomPoint[2]]==1)
hP[6]=1;
end
end
if(leftPoint[2]!=0)
if(imAr[leftPoint[1],leftPoint[2]]==1)
hP[3]=1;
end
end
if(rightPoint[2]!=(w+1))
if(imAr[rightPoint[1],rightPoint[2]]==1)
hP[5]=1;
end
end
# add first elements
if(firstFlag)
locObj1=collect(hP[1]);
locObj2=collect(hP[2]);
locObj3=collect(hP[3]);
locObj4=collect(hP[4]);
locObj5=collect(hP[5]);
locObj6=collect(hP[6]);
firstFlag=false;
else
# if first element of locObj was deleted actual point should not get pushed to array
if(!doNotAdd)
push!(locObj1,hP[1]);
push!(locObj2,hP[2]);
push!(locObj3,hP[3]);
push!(locObj4,hP[4]);
push!(locObj5,hP[5]);
push!(locObj6,hP[6]);
imAr[hP[1],hP[2]]=0;
end
end
goL=false;
goT=false;
goR=false;
goB=false;
doNotAdd=false;
if(length(locObj1)!=0)
# always take and check first elements of locObj
hPfInLoc=[locObj1[1],locObj2[1],locObj3[1],locObj4[1],locObj5[1],locObj6[1]];
hPl=[hPfInLoc[1];hPfInLoc[2]-1;0;0;0;0];
hPt=[hPfInLoc[1]-1;hPfInLoc[2];0;0;0;0];
hPr=[hPfInLoc[1];hPfInLoc[2]+1;0;0;0;0];
hPb=[hPfInLoc[1]+1;hPfInLoc[2];0;0;0;0];
compL=false;
compT=false;
compR=false;
compB=false;
# check bounds and if array values have changed
if(hPt[1]!=0)
if(imAr[hPt[1],hPt[2]]!=0)
compT=true;
end
end
if(hPb[1]!=(h+1))
if(imAr[hPb[1],hPb[2]]!=0)
compB=true;
end
end
if(hPl[2]!=0)
if(imAr[hPl[1],hPl[2]]!=0)
compL=true;
end
end
if(hPr[2]!=(w+1))
if(imAr[hPr[1],hPr[2]]!=0)
compR=true;
end
end
# define directions and set defined direction false in locObj
if((locObj3[1]==1)& compL)
locObj3[1]=0;
goL=true;
elseif((locObj4[1]==1)& compT)
locObj4[1]=0;
goT=true;
elseif((locObj5[1]==1)& compR)
locObj5[1]=0;
goR=true;
elseif((locObj6[1]==1)& compB)
locObj6[1]=0;
goB=true;
else
if (length(locObj1)==1)
locObj=[];
else # if everything is zero delete first rows of arrays
deleteat!(locObj1,1);
deleteat!(locObj2,1);
deleteat!(locObj3,1);
deleteat!(locObj4,1);
deleteat!(locObj5,1);
deleteat!(locObj6,1);
doNotAdd=true;
continue
end
end
end
#execute choosen direction
if(goL)
hP = hPl
continue
end
if(goT)
hP = hPt
continue
end
if(goR)
hP = hPr
continue
end
if(goB)
hP = hPb
continue
end
break
end
end
Somehow the output image turned on its side in my run.