java - executor service. how to await while all threads will terminate -

please understand concurrency problem.

i have following code thread execution:

public void startpool(final processor processor, configuration config) {             executorservice pool = executors.newfixedthreadpool(config.getthreadpoolsize());             (final string source : config.getsourcepaths()) {                 pool.submit(new runnable() {                      @override                     public void run() {                         processor.process(source);                      }                 });             }             pool.shutdown();         } 

when use 1 thread(config.getthreadpoolsize() returns 1) expecetd result.

when use thread count - every time different results. in case result - output console. understand if use lot of threads can different order of output different content!!! sometimes, contents absent. looks 1 thread terminated , other died @ moment.

where can search error? @ code or somewhere deeper?

i see situation on picture:

update:

if rewrite code this:

           @override             public void run() {                 synchronized ("123") {                     processor.process(source);                 }             } 

it working understand not multithreading)

update

problem threadpool swallows exceptions. resolve problem after catching throwable inside processor.process(source); , printstacktrace

it seems processor implementation use not thread-safe: expected output 1 thread not several threads in parallel.

the behavior may unexpected in multi threaded environment.