Merge bitcoin/bitcoin#27189: util: Use steady clock in SeedStrengthen, FindBestImplementation, FlushStateToDisk

fa1b4e5c3294fc9aec033892a4a4d7b5cfc015aa Use steady clock in FlushStateToDisk (MarcoFalke)
1111e2f8b43cd9ed62dcf6b571a224b84fc421fd Use steady clock in SeedStrengthen and FindBestImplementation (MarcoFalke)

Pull request description:

  There may be a theoretical deadlock for the duration of the offset when the system clock is adjusted into a past time while executing `SeedStrengthen`.

  Fix this by using steady clock.

  Do the same in `FindBestImplementation`, which shouldn't be affected, because it discards outlier measurements. However, doing the same there for consistency seems fine.

  Do the same in `FlushStateToDisk`, which should make the flushes more steady, if the system clock is adjusted by a large offset.

ACKs for top commit:
  john-moffett:
    ACK fa1b4e5c3294fc9aec033892a4a4d7b5cfc015aa
  willcl-ark:
    ACK fa1b4e5c3

Tree-SHA512: cc625e796b186accd53222bd64eb57d0512bc7e588312d254349b542bbc5e5daac348ff2b3b3f7dc5ae0bbbae2ec11fdbf3022cf2164211633765a4b0108e83e

1 files changed, 4 insertions, 4 deletions

diff --git a/src/validation.cpp b/src/validation.cpp
index 823d326d18..f3c0401c0f 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2478,12 +2478,12 @@ bool Chainstate::FlushStateToDisk(
                 }
             }
         }
-        const auto nNow = GetTime<std::chrono::microseconds>();
+        const auto nNow{SteadyClock::now()};
         // Avoid writing/flushing immediately after startup.
-        if (m_last_write.count() == 0) {
+        if (m_last_write == decltype(m_last_write){}) {
             m_last_write = nNow;
         }
-        if (m_last_flush.count() == 0) {
+        if (m_last_flush == decltype(m_last_flush){}) {
             m_last_flush = nNow;
         }
         // The cache is large and we're within 10% and 10 MiB of the limit, but we have time now (not in the middle of a block processing).
@@ -2544,7 +2544,7 @@ bool Chainstate::FlushStateToDisk(
             m_last_flush = nNow;
             full_flush_completed = true;
             TRACE5(utxocache, flush,
-                   (int64_t)(GetTimeMicros() - nNow.count()), // in microseconds (µs)
+                   int64_t{Ticks<std::chrono::microseconds>(SteadyClock::now() - nNow)},
                    (uint32_t)mode,
                    (uint64_t)coins_count,
                    (uint64_t)coins_mem_usage,