fix(profiling): restore OPcache restart hook on shutdown

[realFlowControl]

Description

Apache graceful reloads can run MSHUTDOWN followed by another MINIT in the same process. The profiler installed ddog_php_prof_zend_accel_schedule_restart_hook during MINIT but did not restore the previous OPcache restart hook during MSHUTDOWN. The next MINIT could therefore capture the profiler callback as its own predecessor, causing infinite recursion and a stack-overflow SIGSEGV when OPcache scheduled a restart.

This restores the previous OPcache restart hook during timeline shutdown, before a subsequent module initialization can install it again.

Jira: SCP-1307

Testing

Reproduced locally with PHP 8.4.22 NTS, Apache mod_php, OPcache enabled, the profiler loaded. After an Apache graceful reload, opcache_reset() caused the unmodified master worker to exit with SIGSEGV and returned an empty HTTP response. With this change, opcache_reset() returned true over HTTP 200 and Apache logged no signal exit.

• cargo fmt --check
• cargo build -p datadog-php-profiling

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[datadog-datadog-prod-us1-2]

 

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⚠️ Warnings

🚦 4 Pipeline jobs failed

DataDog/apm-reliability/dd-trace-php | test_extension_ci: [8.1]     

DataDog/apm-reliability/dd-trace-php | test_extension_ci: [8.3]     

DataDog/apm-reliability/dd-trace-php | merge-gate     

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ℹ️ Info

No other issues found (see more)

🧪 All tests passed
❄️ No new flaky tests detected

🔄 Datadog auto-retried 1 job - 1 passed on retry

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 60.65% (+0.00%)

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[pr-commenter]

Benchmarks [ profiler ]

Benchmark execution time: 2026-07-29 07:00:21

Comparing candidate commit d1fd7f1 in PR branch florian/scp-1307-restore-opcache-restart-hook with baseline commit 24c4207 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 28 metrics, 8 unstable metrics.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

• 🟩 = significantly better candidate vs. baseline
• 🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'