Aias00 opened a new issue, #7974:
URL: https://github.com/apache/shenyu/issues/7974
### Is there an existing issue for this?
- [x] I have searched the existing issues
### Current Behavior
`AbstractLoadBalancer.select` returns immediately for a singleton candidate
list. This bypasses `P2cLoadBalancer.doSelect`, including its inflight
increment. However, the normal Divide P2C completion callback still decrements
the selected upstream's inflight. Repeated singleton requests therefore make
the counter negative, and P2C subsequently uses that negative value in its load
calculation.
This affects single-upstream deployments and requests where filtering leaves
only one eligible upstream. The explicit half-open probe path has its own
increment and is not the path described here.
### Expected Behavior
Pair start/completion accounting even when selection is short-circuited for
a singleton list. A completed request must not leave a negative or leaked
counter.
### Steps To Reproduce
Configure Divide with `p2c` and one healthy upstream, then complete two
requests. The following reproduces the selection plus the decrement performed
by Divide's completion callback:
```java
var upstream = Upstream.builder().protocol("http://";).url("a:80")
.weight(100).status(true).build();
var balancer = new P2cLoadBalancer();
for (int i = 0; i < 2; i++) {
balancer.select(List.of(upstream), new LoadBalanceData());
upstream.getInflight().decrementAndGet(); // Divide responseTrigger
}
System.out.println(upstream.getInflight().get()); // observed: -1
```
This minimal reproduction was executed against the commit below; the initial
counter is 1.
### Anything else?
- Singleton shortcut:
https://github.com/apache/shenyu/blob/862f5e37e894bd8cef85ef540a8629f313e9ecdf/shenyu-loadbalancer/src/main/java/org/apache/shenyu/loadbalancer/spi/AbstractLoadBalancer.java#L41-L48
- Increment bypassed by the shortcut:
https://github.com/apache/shenyu/blob/862f5e37e894bd8cef85ef540a8629f313e9ecdf/shenyu-loadbalancer/src/main/java/org/apache/shenyu/loadbalancer/spi/P2cLoadBalancer.java#L73
- Unconditional completion decrement:
https://github.com/apache/shenyu/blob/862f5e37e894bd8cef85ef540a8629f313e9ecdf/shenyu-plugin/shenyu-plugin-proxy/shenyu-plugin-divide/src/main/java/org/apache/shenyu/plugin/divide/DividePlugin.java#L215-L217
- #6733 concerned cancellation cleanup. This issue remains with the current
`doFinally` cleanup because the corresponding increment is skipped.
### Environment
- ShenYu: master, 2.7.2-SNAPSHOT
- Commit: `862f5e37e894bd8cef85ef540a8629f313e9ecdf`
- Java 17
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