From 67d3980a2aefaa9962c3011804171fc529dc5b2b Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Sun, 14 May 2023 09:54:16 +0200
Subject: Setup machine interrupt handling infrastructure

---
 bbot/agent/agent.cxx | 105 ++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 70 insertions(+), 35 deletions(-)

diff --git a/bbot/agent/agent.cxx b/bbot/agent/agent.cxx
index 8e0caf6..d58743b 100644
--- a/bbot/agent/agent.cxx
+++ b/bbot/agent/agent.cxx
@@ -1197,8 +1197,13 @@ catch (const system_error& e)
   fail << "unable to iterate over " << machines << ": " << e << endf;
 }
 
+// Perform the build task throwing interrupt if it has been interrupted.
+//
+struct interrupt {};
+
 static result_manifest
-perform_task (machine_lock& ml,
+perform_task (toolchain_lock tl, // Note: assumes ownership.
+              machine_lock& ml,
               const dir_path& md,
               const bootstrapped_machine_manifest& mm,
               const task_manifest& tm)
@@ -1206,6 +1211,8 @@ try
 {
   tracer trace ("perform_task", md.string ().c_str ());
 
+  tl.unlock (); // @@ TMP (we have to arm the signal handler under lock).
+
   result_manifest r {
     tm.name,
     tm.version,
@@ -1226,7 +1233,8 @@ try
   //
   // 3. Start the TFTP server and the machine.
   //
-  // 4. Serve TFTP requests while watching out for the result manifest.
+  // 4. Serve TFTP requests while watching out for the result manifest and
+  //    interrupts.
   //
   // 5. Clean up (force the machine down and delete the snapshot).
   //
@@ -2177,34 +2185,13 @@ try
     //
     task_manifest& t (*tr.task);
 
-    // First verify the requested machine is one of those we sent in tq. Then
-    // find the corresponding bootstrapped_machine instance in ms. Also unlock
-    // all the other machines as well as the global toolchain lock.
+    // First verify the requested machine is one of those we sent in tq.
     //
-    bootstrapped_machine* pm (nullptr);
-    for (const machine_header_manifest& mh: tq.machines)
-    {
-      if (mh.name == t.machine) // Yes, comparing names, not ids.
-      {
-        for (bootstrapped_machine& m: ms)
-        {
-          if (mh.name == m.manifest.machine.name)
-          {
-            m.lock.perform_task (tl, prio);
-            pm = &m;
-          }
-          else
-            m.lock.unlock ();
-        }
-
-        assert (pm != nullptr);
-        break;
-      }
-    }
-
-    tl.unlock ();
-
-    if (pm == nullptr)
+    if (find_if (tq.machines.begin (), tq.machines.end (),
+                 [&t] (const machine_header_manifest& mh)
+                 {
+                   return mh.name == t.machine; // Yes, names, not ids.
+                 }) == tq.machines.end ())
     {
       error << "task from " << url << " for unknown machine " << t.machine;
 
@@ -2214,8 +2201,6 @@ try
       continue;
     }
 
-    bootstrapped_machine& m (*pm);
-
     if (ops.dump_task ())
     {
       serialize_manifest (t, cout, "stdout", "task");
@@ -2237,9 +2222,56 @@ try
     if (!tr.agent_checksum || *tr.agent_checksum != agent_checksum)
       t.worker_checksum = nullopt;
 
-    result_manifest r (perform_task (m.lock, m.path, m.manifest, t));
+    // Handle interrupts.
+    //
+    // Note that the interrupt can be triggered both by another process (the
+    // interrupt exception is thrown from perform_task()) as well as by this
+    // process in case we were unable to interrupt the other process (seeing
+    // that we have already received a task, responding with an interrupt
+    // feels like the most sensible option).
+    //
+    result_manifest r;
+    bootstrapped_machine* pm (nullptr);
+    try
+    {
+      // Next find the corresponding bootstrapped_machine instance in ms. Also
+      // unlock all the other machines.
+      //
+      // @@ TODO: looks like this is also where we will interrupt the machines
+      //          (thus inside the try block). Note that we have to do this
+      //          while holding the toolchain lock. Would be good to
+      //          unlock all the machines as well as the toolchain lock on
+      //          failure.
+      //
+      for (bootstrapped_machine& m: ms)
+      {
+        if (m.manifest.machine.name == t.machine)
+        {
+          assert (pm == nullptr); // Sanity check.
 
-    m.lock.unlock (); // No need to hold the lock any longer.
+          m.lock.perform_task (tl, prio);
+          pm = &m;
+        }
+        else
+          m.lock.unlock ();
+      }
+      assert (pm != nullptr);
+
+      r = perform_task (move (tl), pm->lock, pm->path, pm->manifest, t);
+    }
+    catch (const interrupt&)
+    {
+      r = result_manifest {
+        t.name,
+        t.version,
+        result_status::interrupt,
+        operation_results {},
+        nullopt /* worker_checksum */,
+        nullopt /* dependency_checksum */};
+    }
+
+    if (pm != nullptr) // Let's not assume.
+      pm->lock.unlock (); // No need to hold the lock any longer.
 
     if (ops.dump_result ())
     {
@@ -2279,6 +2311,8 @@ try
       fail << "unable to sign task response challenge: " << e;
     }
 
+    result_status rs (r.status);
+
     // Upload the result.
     //
     result_request_manifest rq {tr.session,
@@ -2337,8 +2371,9 @@ try
       }
     }
 
-    l2 ([&]{trace << "built " << t.name << '/' << t.version << " "
-                  << "on " << t.machine << " "
+    l2 ([&]{trace << "built " << t.name << '/' << t.version << ' '
+                  << "status " << rs << ' '
+                  << "on " << t.machine << ' '
                   << "for " << url;});
   }
 }
-- 
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