My last question to this topic and the corresponding answer did not explain all details. So I decide to simplify the code:
List<String> wis = new ArrayList<String>();
for(int i=0;i<3000;i++) {
wis.add("test_" + i);
}
DayCalc calc = new DayCalc();
List<List<String>> partition = MyPartition.partition(wis, 30);
ExecutorService executor = Executors.newFixedThreadPool(4);
for(List<String> part: partition) {
Runnable worker = new DayCalcWorker(part, calc);
executor.execute(worker);
}
executor.shutdown();
while (!executor.isTerminated()) {
// Execute all Threads
}
The shared class object "calc" is used by all executed threads:
public class DayCalc {
private static int CURRENT_DAY_OF_YEAR = DateTimes.getCurrentCalendarDay();
ArrayList<String> kwContentArray;
public DayCalc() {
kwContentArray = new ArrayList<String>();
}
private int getCurrentCalendarDay(Calendar cal) {
// Reset time to start of day (00:00)
cal.set(Calendar.HOUR, 0);
cal.set(Calendar.MINUTE, 0);
// Get starting day
Calendar currentTime2 = StartDate.getStartDate();
System.out.println("Day: " + CURRENT_DAY_OF_YEAR);
System.out.println("Start Date: " + currentTime2.getTime());
int day = (int) Convert.daysBetween(currentTime2.getTime(), cal.getTime());
return day;
}
public void setValueFromWorkItem(String wiID, String duration, Calendar cal) {
if (duration != null) {
this.setDurationValues(wiID, duration, cal);
} else {
int currentDay = getCurrentCalendarDay(cal);
long time = 0;
kwContentArray.add(String.valueOf(time));
}
}
// [...]
}
Thread Worker class:
public class DayCalcWorker implements Runnable {
private List<String> wis;
private DayCalc dayCalc;
GregorianCalendar cal = new GregorianCalendar();
GregorianCalendar cal2 = new GregorianCalendar();
public DayCalcWorker(List<String> wis, DayCalc dayCalc) {
this.wis = wis;
this.dayCalc = dayCalc;
}
@Override
public void run() {
if (wis != null && wis.size() > 0) {
for(String wi: wis) {
long randomDate = System.currentTimeMillis() + Random.getValue();
cal.setTime(new Date(randomDate));
dayCalc.setValueFromWorkItem(wi, "24", cal);
}
}
}
}
Question
Is it save not to synchronize the methods setValueFromWorkItem
or getCurrentCalendarDay
because they use e.g. only a local created calendar object from each Worker thread?
Because the object calc
from the class DayCalc
is shared I have only to keep care of objects which are created within this class and not with passed objects from Worker Threads which are calling methods of calc
, haven't I?
Note that the code itself makes no sence at all. It just should explain that I use mutable calendar objects which need to synchronized (maybe).