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[LL FIR] fix more possible NPEs at lock access

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Depending on the execution, some accesses to lock could cause NPE.
The best solution we've found so far is to make lock volatile, so that
reads between lock and value are consistent between threads.
It requires further work to determine if we can have one volatile field.
This commit is contained in:
Artem Vasilev
2022-12-16 15:34:27 +01:00
committed by Space Team
parent 04924dbfed
commit 1e1f96f73e
1 changed files with 14 additions and 8 deletions
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analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/caches/ValueWithPostCompute.kt
+14 -8
View File
@@ -14,7 +14,7 @@ import java.util.concurrent.locks.ReentrantLock
* assuming that postCompute may try to read that value inside current thread,
* So in the period then value is calculated but post compute was not finished,
* only thread that initiated the calculating may see the value,
* other threads will have to wait wait until that value is calculated
* other threads will have to wait until that value is calculated
*/
internal class ValueWithPostCompute<KEY, VALUE, DATA>(
/**
@@ -26,6 +26,11 @@ internal class ValueWithPostCompute<KEY, VALUE, DATA>(
) {
private var _calculate: ((KEY) -> Pair<VALUE, DATA>)? = calculate
private var _postCompute: ((KEY, VALUE, DATA) -> Unit)? = postCompute
/**
* [lock] being volatile ensures the consistent reads between [lock] and [value] in different threads.
*/
@Volatile
private var lock: ReentrantLock? = ReentrantLock()
/**
@@ -35,7 +40,7 @@ internal class ValueWithPostCompute<KEY, VALUE, DATA>(
* [ValueIsPostComputingNow] -- thread with threadId has computed the value and only it can access it during post compute
* some value of type [VALUE] -- value is computed and post compute was executed, values is visible for all threads
*
* Value may be set only under [LazyValueWithPostCompute] intrinsic lock hold
* Value may be set only under [ValueWithPostCompute] intrinsic lock hold
* And may be read from any thread
*/
@Volatile
@@ -55,7 +60,7 @@ internal class ValueWithPostCompute<KEY, VALUE, DATA>(
if (stateSnapshot.threadId == Thread.currentThread().id) {
return stateSnapshot.value as VALUE
} else {
lock!!.lockWithPCECheck(LOCKING_INTERVAL_MS) { // wait until other thread which holds the lock now computes the value
lock?.lockWithPCECheck(LOCKING_INTERVAL_MS) { // wait until other thread which holds the lock now computes the value
when (val newStateSnapshot = value) {
ValueIsNotComputed -> {
// if we have a PCE during value computation, then we will enter the critical section with `value == ValueIsNotComputed`
@@ -71,12 +76,13 @@ internal class ValueWithPostCompute<KEY, VALUE, DATA>(
return value as VALUE
}
}
}
} ?: return value as VALUE
}
}
ValueIsNotComputed -> lock!!.lockWithPCECheck(LOCKING_INTERVAL_MS) {
ValueIsNotComputed -> lock?.lockWithPCECheck(LOCKING_INTERVAL_MS) {
return computeValueWithoutLock()
}
} ?: return value as VALUE
is ExceptionWasThrownDuringValueComputation -> {
throw stateSnapshot.error
}
@@ -104,7 +110,6 @@ internal class ValueWithPostCompute<KEY, VALUE, DATA>(
else -> {
// other thread computed the value for us and set `lock` to null
require(lock == null)
return value as VALUE
}
}
@@ -124,10 +129,11 @@ internal class ValueWithPostCompute<KEY, VALUE, DATA>(
}
throw e
}
// reading lock = null implies that the value is calculated and stored
value = calculatedValue
_calculate = null
_postCompute = null
lock = null
value = calculatedValue
return calculatedValue
}