libstore: encapsulate worker build hook state

once goals run on multiple threads these fields must by synchronized as
one, or we try to run build hooks to often (or worse, not often enough)

Change-Id: I47860e46fe5c6db41755b2a3a1d9dbb5701c4ca4

src/libstore/build/derivation-goal.cc

@@ -1127,21 +1127,21 @@ void DerivationGoal::resolvedFinished()
 
 HookReply DerivationGoal::tryBuildHook()
 {
-    if (!worker.tryBuildHook || !useDerivation) return rpDecline;
+    if (!worker.hook.available || !useDerivation) return rpDecline;
 
-    if (!worker.hook)
+    if (!worker.hook.instance)
-        worker.hook = std::make_unique<HookInstance>();
+        worker.hook.instance = std::make_unique<HookInstance>();
 
     try {
 
         /* Send the request to the hook. */
-        worker.hook->sink
+        worker.hook.instance->sink
             << "try"
             << (worker.getNrLocalBuilds() < settings.maxBuildJobs ? 1 : 0)
             << drv->platform
             << worker.store.printStorePath(drvPath)
             << parsedDrv->getRequiredSystemFeatures();
-        worker.hook->sink.flush();
+        worker.hook.instance->sink.flush();
 
         /* Read the first line of input, which should be a word indicating
            whether the hook wishes to perform the build. */
@@ -1149,13 +1149,13 @@ HookReply DerivationGoal::tryBuildHook()
         while (true) {
             auto s = [&]() {
                 try {
-                    return readLine(worker.hook->fromHook.readSide.get());
+                    return readLine(worker.hook.instance->fromHook.readSide.get());
                 } catch (Error & e) {
                     e.addTrace({}, "while reading the response from the build hook");
                     throw;
                 }
             }();
-            if (handleJSONLogMessage(s, worker.act, worker.hook->activities, true))
+            if (handleJSONLogMessage(s, worker.act, worker.hook.instance->activities, true))
                 ;
             else if (s.substr(0, 2) == "# ") {
                 reply = s.substr(2);
@@ -1172,8 +1172,8 @@ HookReply DerivationGoal::tryBuildHook()
         if (reply == "decline")
             return rpDecline;
         else if (reply == "decline-permanently") {
-            worker.tryBuildHook = false;
+            worker.hook.available = false;
-            worker.hook = 0;
+            worker.hook.instance.reset();
             return rpDecline;
         }
         else if (reply == "postpone")
@@ -1185,14 +1185,14 @@ HookReply DerivationGoal::tryBuildHook()
         if (e.errNo == EPIPE) {
             printError(
                 "build hook died unexpectedly: %s",
-                chomp(drainFD(worker.hook->fromHook.readSide.get())));
+                chomp(drainFD(worker.hook.instance->fromHook.readSide.get())));
-            worker.hook = 0;
+            worker.hook.instance.reset();
             return rpDecline;
         } else
             throw;
     }
 
-    hook = std::move(worker.hook);
+    hook = std::move(worker.hook.instance);
 
     try {
         machineName = readLine(hook->fromHook.readSide.get());

src/libstore/build/worker.hh

@@ -135,7 +135,17 @@ public:
     Store & store;
     Store & evalStore;
 
-    std::unique_ptr<HookInstance> hook;
+    struct HookState {
+        std::unique_ptr<HookInstance> instance;
+
+        /**
+         * Whether to ask the build hook if it can build a derivation. If
+         * it answers with "decline-permanently", we don't try again.
+         */
+        bool available = true;
+    };
+
+    HookState hook;
 
     uint64_t expectedBuilds = 0;
     uint64_t doneBuilds = 0;
@@ -151,12 +161,6 @@ public:
     uint64_t expectedNarSize = 0;
     uint64_t doneNarSize = 0;
 
-    /**
-     * Whether to ask the build hook if it can build a derivation. If
-     * it answers with "decline-permanently", we don't try again.
-     */
-    bool tryBuildHook = true;
-
     Worker(Store & store, Store & evalStore);
     ~Worker();