CompletableFuture and Happens-before Order
I intend to create 2 threads to do some computation then checking (each of them) whether the other also completed its computation otherwise simply exit. When thread1 finds out that the other (thread2) also completed its computation then thread1 should continue with an additional computation based on the result of thread2 (otherwise would simply exit).
So I intend to use the Runnable below with 2 threads like this:
me = new CompletableFuture<>();
theOther = new CompletableFuture<>();
executorService.submit(createWorker(data, true, me, theOther));
executorService.submit(createWorker(data++, false, theOther, me));
and the Runnable is created this way:
private Runnable createWorker(int data, boolean callRegion1,
CompletableFuture<Payment> me,
CompletableFuture<Payment> theOther) {
return () -> {
Payment myPayment;
try {
myPayment = postData(data, callRegion1);
me.complete(myPayment);
} catch (Throwable ex) {
me.completeExceptionally(ex);
// comparison with theOther no longer make sense
return;
}
// skip comparison when myPayment is null
if (myPayment == null) {
log.error("myPayment == null for data = {}", data);
return;
}
// get otherPayment and ignore exceptions
Payment otherPayment = theOther.getNow(absentPayment);
// skip comparison when otherPayment is null or not yet available
if (otherPayment == null || otherPayment == absentPayment) {
return;
}
// doing the comparison here
if (otherPayment.getData() + myPayment.getData() != 0) {
log.error("M/M or M/SM for data = {}", data);
System.exit(-1);
}
};
}
The created Runnable is not explicitly synchronized so I fear that the code below:
theOther.getNow(absentPayment);
might be evaluated to absentPayment the same time by both threads which would be bad for me (let's name this the bad scenario).
Q: Is the bad scenario possible and why? if not possible, again why not?
java jls happens-before
asked Dec 28 '18 at 23:43
adrhcadrhc
445314
add a comment |
I intend to create 2 threads to do some computation then checking (each of them) whether the other also completed its computation otherwise simply exit. When thread1 finds out that the other (thread2) also completed its computation then thread1 should continue with an additional computation based on the result of thread2 (otherwise would simply exit).
So I intend to use the Runnable below with 2 threads like this:
me = new CompletableFuture<>();
theOther = new CompletableFuture<>();
executorService.submit(createWorker(data, true, me, theOther));
executorService.submit(createWorker(data++, false, theOther, me));
and the Runnable is created this way:
private Runnable createWorker(int data, boolean callRegion1,
CompletableFuture<Payment> me,
CompletableFuture<Payment> theOther) {
return () -> {
Payment myPayment;
try {
myPayment = postData(data, callRegion1);
me.complete(myPayment);
} catch (Throwable ex) {
me.completeExceptionally(ex);
// comparison with theOther no longer make sense
return;
}
// skip comparison when myPayment is null
if (myPayment == null) {
log.error("myPayment == null for data = {}", data);
return;
}
// get otherPayment and ignore exceptions
Payment otherPayment = theOther.getNow(absentPayment);
// skip comparison when otherPayment is null or not yet available
if (otherPayment == null || otherPayment == absentPayment) {
return;
}
// doing the comparison here
if (otherPayment.getData() + myPayment.getData() != 0) {
log.error("M/M or M/SM for data = {}", data);
System.exit(-1);
}
};
}
The created Runnable is not explicitly synchronized so I fear that the code below:
theOther.getNow(absentPayment);
might be evaluated to absentPayment the same time by both threads which would be bad for me (let's name this the bad scenario).
Q: Is the bad scenario possible and why? if not possible, again why not?
java jls happens-before
asked Dec 28 '18 at 23:43
adrhcadrhc
445314
add a comment |
I intend to create 2 threads to do some computation then checking (each of them) whether the other also completed its computation otherwise simply exit. When thread1 finds out that the other (thread2) also completed its computation then thread1 should continue with an additional computation based on the result of thread2 (otherwise would simply exit).
So I intend to use the Runnable below with 2 threads like this:
me = new CompletableFuture<>();
theOther = new CompletableFuture<>();
executorService.submit(createWorker(data, true, me, theOther));
executorService.submit(createWorker(data++, false, theOther, me));
and the Runnable is created this way:
private Runnable createWorker(int data, boolean callRegion1,
CompletableFuture<Payment> me,
CompletableFuture<Payment> theOther) {
return () -> {
Payment myPayment;
try {
myPayment = postData(data, callRegion1);
me.complete(myPayment);
} catch (Throwable ex) {
me.completeExceptionally(ex);
// comparison with theOther no longer make sense
return;
}
// skip comparison when myPayment is null
if (myPayment == null) {
log.error("myPayment == null for data = {}", data);
return;
}
// get otherPayment and ignore exceptions
Payment otherPayment = theOther.getNow(absentPayment);
// skip comparison when otherPayment is null or not yet available
if (otherPayment == null || otherPayment == absentPayment) {
return;
}
// doing the comparison here
if (otherPayment.getData() + myPayment.getData() != 0) {
log.error("M/M or M/SM for data = {}", data);
System.exit(-1);
}
};
}
The created Runnable is not explicitly synchronized so I fear that the code below:
theOther.getNow(absentPayment);
might be evaluated to absentPayment the same time by both threads which would be bad for me (let's name this the bad scenario).
Q: Is the bad scenario possible and why? if not possible, again why not?
java jls happens-before
asked Dec 28 '18 at 23:43
adrhcadrhc
445314
I intend to create 2 threads to do some computation then checking (each of them) whether the other also completed its computation otherwise simply exit. When thread1 finds out that the other (thread2) also completed its computation then thread1 should continue with an additional computation based on the result of thread2 (otherwise would simply exit).
So I intend to use the Runnable below with 2 threads like this:
me = new CompletableFuture<>();
theOther = new CompletableFuture<>();
executorService.submit(createWorker(data, true, me, theOther));
executorService.submit(createWorker(data++, false, theOther, me));
and the Runnable is created this way:
private Runnable createWorker(int data, boolean callRegion1,
CompletableFuture<Payment> me,
CompletableFuture<Payment> theOther) {
return () -> {
Payment myPayment;
try {
myPayment = postData(data, callRegion1);
me.complete(myPayment);
} catch (Throwable ex) {
me.completeExceptionally(ex);
// comparison with theOther no longer make sense
return;
}
// skip comparison when myPayment is null
if (myPayment == null) {
log.error("myPayment == null for data = {}", data);
return;
}
// get otherPayment and ignore exceptions
Payment otherPayment = theOther.getNow(absentPayment);
// skip comparison when otherPayment is null or not yet available
if (otherPayment == null || otherPayment == absentPayment) {
return;
}
// doing the comparison here
if (otherPayment.getData() + myPayment.getData() != 0) {
log.error("M/M or M/SM for data = {}", data);
System.exit(-1);
}
};
}
The created Runnable is not explicitly synchronized so I fear that the code below:
theOther.getNow(absentPayment);
might be evaluated to absentPayment the same time by both threads which would be bad for me (let's name this the bad scenario).
Q: Is the bad scenario possible and why? if not possible, again why not?
java jls happens-before
java jls happens-before
asked Dec 28 '18 at 23:43
adrhcadrhc
445314
asked Dec 28 '18 at 23:43
adrhcadrhc
445314
edited Dec 29 '18 at 0:16
adrhc
asked Dec 28 '18 at 23:43
adrhcadrhc
445314
asked Dec 28 '18 at 23:43
adrhcadrhc
445314
asked Dec 28 '18 at 23:43
adrhcadrhc
445314
445314
add a comment |
add a comment |
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