RFR: 8308094: Add a compilation timeout flag to catch long running compilations [v5]

[Dean Long]

On Fri, 8 Aug 2025 10:51:42 GMT, Manuel Hässig <mhaessig at openjdk.org> wrote:

>> This PR adds `-XX:CompileTaskTimeout` on Linux to limit the amount of time a compilation task can run. The goal of this is initially to be able to find and investigate long-running compilations.
>> 
>> The timeout is implemented using a POSIX timer that sends a `SIGALRM` to the compiler thread the compile task is running on. Each compiler thread registers a signal handler that triggers an assert upon receiving `SIGALRM`. This is currently only implemented for Linux, because it relies on `SIGEV_THREAD_ID` to get the signal delivered to the same thread that timed out.
>> 
>> Since `SIGALRM` is now used, the test `runtime/signal/TestSigalrm.java` now requires `vm.flagless` so it will not interfere with the compiler thread signal handlers.
>> 
>> Testing:
>>  - [x] Github Actions
>>  - [x] tier1, tier2 on all platforms
>>  - [x] tier3, tier4 and Oracle internal testing on Linux fastdebug
>>  - [x] tier1 through tier4 with `-XX:CompileTaskTimeout=60000` (one minute timeout) to see what fails (`compiler/codegen/TestAntiDependenciesHighMemUsage2.java`, `compiler/loopopts/TestMaxLoopOptsCountReached.java`, and `compiler/c2/TestScalarReplacementMaxLiveNodes.java` fail)
>
> Manuel Hässig has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 11 additional commits since the last revision:
> 
>  - Merge branch 'master' into JDK-8308094-timeout
>  - Rename _timer
>  - remove _timeout_armed
>  - ASSERT
>  - Merge branch 'master' into JDK-8308094-timeout
>  - No acquire release semantics
>  - Factor Linux specific timeout functionality out of share/
>  - Move timeout disarm above if
>  - Merge branch 'master' into JDK-8308094-timeout
>  - Fix SIGALRM test
>  - ... and 1 more: https://git.openjdk.org/jdk/compare/2eac5347...8bb5eb7a

Marked as reviewed by dlong (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/26023#pullrequestreview-3101863176