fix: preventing DROP DATABASE from completing

When doing `CREATE DATABASE foo` and then `DROP DATABASE foo`, the
command stuck waiting showing:

```
2025-07-30 08:29:22.191 -05 [265233] LOG:  still waiting for backend with PID 265223 to accept ProcSignalBarrier
...
```

This happened because DROP DATABASE sends a SIGUSR1 to all backends and
we use the potsgres default SIGUSR1 handler
(`procsignal_sigusr1_handler`), which didn't wake the worker to reach
`CHECK_FOR_INTERRUPTS()`.

Now we use a custom sigusr1 that does `SetLatch` (waking the worker) and calls the default pg SIGUSR1 handler.

Author: steve-chavez

src/worker.c

@@ -139,6 +139,22 @@ handle_sighup(__attribute__ ((unused)) SIGNAL_ARGS)
   errno = save_errno;
 }
 
+/*
+ *We have to handle sigusr1 explicitly because the default
+ *procsignal_sigusr1_handler doesn't `SetLatch`, this would prevent
+ *DROP DATATABASE from finishing since our worker would be sleeping and not reach
+ *CHECK_FOR_INTERRUPTS()
+ */
+static void
+handle_sigusr1(SIGNAL_ARGS)
+{
+  int     save_errno = errno;
+  if (worker_state)
+    SetLatch(&worker_state->latch);
+  errno = save_errno;
+  procsignal_sigusr1_handler(postgres_signal_arg);
+}
+
 static void publish_state(WorkerStatus s) {
   pg_atomic_write_u32(&worker_state->status, (uint32)s);
   pg_write_barrier();
@@ -219,7 +235,7 @@ void pg_net_worker(__attribute__ ((unused)) Datum main_arg) {
   BackgroundWorkerUnblockSignals();
   pqsignal(SIGTERM, handle_sigterm);
   pqsignal(SIGHUP, handle_sighup);
-  pqsignal(SIGUSR1, procsignal_sigusr1_handler);
+  pqsignal(SIGUSR1, handle_sigusr1);
 
   BackgroundWorkerInitializeConnection(guc_database_name, guc_username, 0);
   pgstat_report_appname("pg_net " EXTVERSION); // set appname for pg_stat_activity

test/test_worker_behavior.py

@@ -7,6 +7,20 @@
 import subprocess
 import os
 
+def test_worker_will_not_block_drop_database(autocommit_sess):
+    """the worker will not block a session doing drop database"""
+
+    autocommit_sess.execute(text("create database foo;"))
+    autocommit_sess.execute(text("drop database foo;"))
+
+    (result,) = autocommit_sess.execute(text("""
+        select 1
+    """)).fetchone()
+
+    assert result is not None
+    assert result == 1
+
+
 def test_success_when_worker_is_up(sess):
     """net.check_worker_is_up should not return anything when the worker is running"""
 
@@ -433,3 +447,4 @@ def test_processing_survives_postmaster_crash():
     tmp_sess.execute(text("select net.wait_until_running()"))
 
     engine.dispose()
+