worker: let a stop request interrupt the reconnect backoff

The retry sleep polled only fShutdown, while the loop around it polls
fShutdown, fGenerateBitcoins and nMineMode. That was survivable at a flat
10s. Raising the ceiling to 120s made it expensive: after an operator
cleared Generate or switched to Relay mode, the participant session --
and the vfThreadRunning[3] slot that gates restarting it -- stayed held
for up to two minutes.

Measured with the loop shape replicated and the stop condition flipped 1s
into a 120s sleep: 119.01s to notice before, 1.00s after, via either
fGenerateBitcoins or nMineMode. The fShutdown path is unchanged at 1.00s.

It also narrows the window on a pre-existing unsynchronised read of
vfThreadRunning[3] at gui.cpp:901, where a stop-then-start inside it
leaves mining silently not restarted.

1 files changed, 10 insertions, 1 deletions

diff --git a/src/main.cpp b/src/main.cpp
index 69b2c32..b0cdab2 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -4418,7 +4418,16 @@ bool BitcoinMiner(int nThreadId)
                 }
                 LogPrint("worker", "PoolParticipantMiner: reconnecting in %ds\n",
                          nRetrySecs);
-                for (int i = 0; i < nRetrySecs && !fShutdown; i++) Sleep(1000);
+                // Poll everything the enclosing while polls, not just
+                // fShutdown. Raising the ceiling to 120s made a
+                // shutdown-only predicate expensive: after the operator
+                // clears Generate or switches to Relay, the session -- and
+                // the vfThreadRunning[3] slot that gates restarting it --
+                // would stay held for up to two minutes. Measured 119s
+                // before, 1s after.
+                for (int i = 0; i < nRetrySecs && !fShutdown && fGenerateBitcoins
+                                && nMineMode == MINE_PARTICIPANT; i++)
+                    Sleep(1000);
                 if (!fHadSession && nRetrySecs < 120) {
                     nRetrySecs *= 2;
                     if (nRetrySecs > 120)