Now I know the reason for the crashes. I did a lot of log writing when creating my reports (they use OSSubprocess).
This was only for debugging. Removing them removed the problem. OSProcess and OSSubprocess are not guilty :-)
I can crash the image with this (try several times)
(in /opt/local/bin/convert there is imagemagick):
1000 timesRepeat: [
| theFileName theStream thePath theFullPathAndFilename isFileNew |
OSSUnixSubprocess new
shellCommand: '/opt/local/bin/convert -background white -alpha remove -density 200 /Library/WebServer/Documents/reports/201801231322-419088218-250457/20170227_19_messdefuerhunde_Fahrten.pdf /Library/WebServer/Documents/reports/201801231322-419088218-250457/20170227_19_messdefuerhunde_Fahrten_%02d.png';
redirectStdout;
run.
thePath := '/data/db/' ��asFileReference.
thePath exists
ifFalse: [ thePath createDirectory ].
theFileName := 'HALLO_' , Date today yyyymmdd , '.txt'.
theFullPathAndFilename := ('/data/db/' ��, theFileName) asFileReference .
theFullPathAndFilename asFileReference exists
ifTrue: [ isFileNew := false.
theStream := MultiByteFileStream oldFileNamed: theFullPathAndFilename.
theStream position: theStream size.
theStream crlf ]
ifFalse: [ isFileNew := true.
theStream := MultiByteFileStream newFileNamed: theFullPathAndFilename ].
[ isFileNew
ifTrue: [ theStream
nextPutAll: Time now printString;
nextPutAll: Time now printString;
nextPutAll: Time now printString;
nextPutAll: Time now printString;
nextPutAll: Time now printString;
nextPutAll: Time now printString;
nextPutAll: Time now printString;
crlf ].
theStream nextPutAll:'' ]
ensure: [ theStream close ].
].