"what “thread safe” really means…in practical terms" Code Answer

given that a collection, for instance, is not threasafe:

var mydic = new dictionary<string, string>();

in a multhread environment, this will throw:

string s = null;
if (!mydic.trygetvalue("keyname", out s)) {
    s = new string('#', 10);
    mydic.add("keyname", s);
}

as one thread is working trying to add the keyvaluepair to the dictionary mydic, another one may trygetvalue(). as collections can't be read and written at the same time, an exception will occur.

however, on the other hand, if you try this:

// other threads will wait here until the variable mydic gets unlocked from the preceding thread that has locked it.
lock (mydic) {
    string s = null;
    if (!mydic.trygetvalue("keyname", out s)) {
        s = new string('#', 10);
        mydic.add("keyname", s);
    }
} // the first thread that locked the mydic variable will now release the lock so that other threads will be able to work with the variable.

then suddenly, the second thread trying to get the same "keyname" key value will not have to add it to the dictionary as the first thread already added it.

so in short, threadsafe means that an object supports being used by multiple threads at the same time, or will lock the threads appropriately for you, without you having to worry about threadsafety.

2. i don't think ghostscript is now threadsafe. it is majorly using multiple threads to perform its tasks, so this makes it deliver a greater performance, that's all.

3. depending on your budget and your requirements, it may be worthy. but if you build around wrapper, you could perhaps only lock() where it is convenient to do so, or if you do not use multithreading yourself, it is definitely not worth to pay for threadsafety. this means only that if your application uses multithreading, then you will not suffer the consequences of a library not being threadsafe. unless you really multihread, it is not worth paying for a threadsafe library.