Merged R9217

src/libstore/build.cc

@@ -183,6 +183,9 @@ private:
     WeakGoalMap derivationGoals;
     WeakGoalMap substitutionGoals;
 
+    /* Goals waiting for busy paths to be unlocked. */
+    WeakGoals waitingForAnyGoal;
+    
 public:
 
     Worker();
@@ -224,6 +227,10 @@ public:
        get info about `storePath' (with --query-info).  We combine
        substituter invocations to reduce overhead. */
     void waitForInfo(GoalPtr goal, Path sub, Path storePath);
+
+    /* Wait for any goal to finish.  Pretty indiscriminate way to
+       wait for some resource that some other goal is holding. */
+    void waitForAnyGoal(GoalPtr goal);
     
     /* Loop until the specified top-level goals have finished. */
     void run(const Goals & topGoals);
@@ -654,7 +661,7 @@ private:
     void buildDone();
 
     /* Is the build hook willing to perform the build? */
-    typedef enum {rpAccept, rpDecline, rpPostpone, rpDone} HookReply;
+    typedef enum {rpAccept, rpDecline, rpPostpone, rpDone, rpRestart} HookReply;
     HookReply tryBuildHook();
 
     /* Synchronously wait for a build hook to finish. */
@@ -663,9 +670,13 @@ private:
     /* Acquires locks on the output paths and gathers information
        about the build (e.g., the input closures).  During this
        process its possible that we find out that the build is
-       unnecessary, in which case we return false (this is not an
+       unnecessary, in which case we return prDone.  It's also
-       error condition!). */
+       possible that some other goal is already building/substituting
-    bool prepareBuild();
+       the output paths, in which case we return prRestart (go back to
+       the haveDerivation() state).  Otherwise, prProceed is
+       returned. */
+    typedef enum {prProceed, prDone, prRestart} PrepareBuildReply;
+    PrepareBuildReply prepareBuild();
 
     /* Start building a derivation. */
     void startBuilder();
@@ -805,6 +816,20 @@ void DerivationGoal::haveDerivation()
         return;
     }
 
+    /* If this is a fixed-output derivation, it is possible that some
+       other goal is already building the output paths.  (The case
+       where some other process is building it is handled through
+       normal locking mechanisms.)  So if any output paths are already
+       being built, put this goal to sleep. */
+    for (PathSet::iterator i = invalidOutputs.begin();
+         i != invalidOutputs.end(); ++i)
+        if (pathIsLockedByMe(*i)) {
+            /* Wait until any goal finishes (hopefully the one that is
+               locking *i), then retry haveDerivation(). */
+            worker.waitForAnyGoal(shared_from_this());
+            return;
+        }
+
     /* We are first going to try to create the invalid output paths
        through substitutes.  If that doesn't work, we'll build
        them. */
@@ -898,6 +923,12 @@ void DerivationGoal::tryToBuild()
                 /* Somebody else did it. */
                 amDone(ecSuccess);
                 return;
+            case rpRestart:
+                /* Somebody else is building this output path.
+                   Restart from haveDerivation(). */
+                state = &DerivationGoal::haveDerivation;
+                worker.waitForAnyGoal(shared_from_this());
+                return;
         }
 
         /* Make sure that we are allowed to start a build. */
@@ -908,9 +939,14 @@ void DerivationGoal::tryToBuild()
 
         /* Acquire locks and such.  If we then see that the build has
            been done by somebody else, we're done. */
-        if (!prepareBuild()) {
+        PrepareBuildReply preply = prepareBuild();
+        if (preply == prDone) {
             amDone(ecSuccess);
             return;
+        } else if (preply == prRestart) {
+            state = &DerivationGoal::haveDerivation;
+            worker.waitForAnyGoal(shared_from_this());
+            return;
         }
 
         /* Okay, we have to build. */
@@ -1209,11 +1245,12 @@ DerivationGoal::HookReply DerivationGoal::tryBuildHook()
 
         /* Acquire locks and such.  If we then see that the output
            paths are now valid, we're done. */
-        if (!prepareBuild()) {
+        PrepareBuildReply preply = prepareBuild();
+        if (preply == prDone || preply == prRestart) {
             /* Tell the hook to exit. */
             writeLine(toHook.writeSide, "cancel");
             terminateBuildHook();
-            return rpDone;
+            return preply == prDone ? rpDone : rpRestart;
         }
 
         printMsg(lvlInfo, format("running hook to build path(s) %1%")
@@ -1289,11 +1326,27 @@ void DerivationGoal::terminateBuildHook(bool kill)
 }
 
 
-bool DerivationGoal::prepareBuild()
+DerivationGoal::PrepareBuildReply DerivationGoal::prepareBuild()
 {
+    /* Check for the possibility that some other goal in this process
+       has locked the output since we checked in haveDerivation().
+       (It can't happen between here and the lockPaths() call below
+       because we're not allowing multi-threading.) */
+    for (DerivationOutputs::iterator i = drv.outputs.begin(); 
+         i != drv.outputs.end(); ++i)
+        if (pathIsLockedByMe(i->second.path)) {
+            debug(format("restarting derivation `%1%' because `%2%' is locked by another goal")
+                % drvPath % i->second.path);
+            return prRestart;
+        }
+    
     /* Obtain locks on all output paths.  The locks are automatically
        released when we exit this function or Nix crashes. */
     /* !!! BUG: this could block, which is not allowed. */
+    /* !!! and once we make this non-blocking, we should carefully
+       consider the case where some but not all locks are required; we
+       should then release the acquired locks so that the other
+       processes and the pathIsLockedByMe() test don't get confused. */
     outputLocks.lockPaths(outputPaths(drv.outputs),
         (format("waiting for lock on %1%") % showPaths(outputPaths(drv.outputs))).str());
 
@@ -1309,7 +1362,7 @@ bool DerivationGoal::prepareBuild()
         debug(format("skipping build of derivation `%1%', someone beat us to it")
             % drvPath);
         outputLocks.setDeletion(true);
-        return false;
+        return prDone;
     }
 
     if (validPaths.size() > 0) {
@@ -1380,7 +1433,7 @@ bool DerivationGoal::prepareBuild()
     allPaths.insert(inputPaths.begin(), inputPaths.end());
     allStatePaths.insert(inputStatePaths.begin(), inputStatePaths.end());
 
-    return true;
+    return prProceed;
 }
 
 
@@ -2171,6 +2224,17 @@ void SubstitutionGoal::tryToRun()
         return;
     }
 
+    /* Maybe a derivation goal has already locked this path
+       (exceedingly unlikely, since it should have used a substitute
+       first, but let's be defensive). */
+    outputLock.reset(); // make sure this goal's lock is gone
+    if (pathIsLockedByMe(storePath)) {
+        debug(format("restarting substitution of `%1%' because it's locked by another goal")
+            % storePath);
+        worker.waitForAnyGoal(shared_from_this());
+        return; /* restart in the tryToRun() state when another goal finishes */
+    }
+    
     /* Acquire a lock on the output path. */
     outputLock = boost::shared_ptr<PathLocks>(new PathLocks);
     outputLock->lockPaths(singleton<PathSet>(storePath),
@@ -2400,6 +2464,16 @@ void Worker::removeGoal(GoalPtr goal)
         if (goal->getExitCode() == Goal::ecFailed && !keepGoing)
             topGoals.clear();
     }
+
+    /* Wake up goals waiting for any goal to finish. */
+    for (WeakGoals::iterator i = waitingForAnyGoal.begin();
+         i != waitingForAnyGoal.end(); ++i)
+    {
+        GoalPtr goal = i->lock();
+        if (goal) wakeUp(goal);
+    }
+
+    waitingForAnyGoal.clear();
 }
 
 
@@ -2486,6 +2560,13 @@ void Worker::waitForInfo(GoalPtr goal, Path sub, Path storePath)
 }
 
 
+void Worker::waitForAnyGoal(GoalPtr goal)
+{
+    debug("wait for any goal");
+    waitingForAnyGoal.insert(goal);
+}
+
+
 void Worker::getInfo()
 {
     for (map<Path, PathSet>::iterator i = requestedInfo.begin();

src/libstore/pathlocks.cc

@@ -223,5 +223,12 @@ void PathLocks::setDeletion(bool deletePaths)
     this->deletePaths = deletePaths;
 }
 
+
+bool pathIsLockedByMe(const Path & path)
+{
+    Path lockPath = path + ".lock";
+    return lockedPaths.find(lockPath) != lockedPaths.end();
+}
+
  
 }

src/libstore/pathlocks.hh

@@ -40,6 +40,9 @@ public:
 };
 
 
+bool pathIsLockedByMe(const Path & path);
+
+
 }
 
 

src/libstore/worker-protocol.hh

@@ -58,9 +58,12 @@ typedef enum {
 #define STDERR_ERROR 0x63787470
 
 
-/* The default location of the daemon socket, relative to
+/* The default location of the daemon socket, relative to nixStateDir.
-   nixStateDir. */
+   The socket is in a directory to allow you to control access to the
-#define DEFAULT_SOCKET_PATH "/daemon.socket"
+   Nix daemon by setting the mode/ownership of the directory
+   appropriately.  (This wouldn't work on the socket itself since it
+   must be deleted and recreated on startup.) */
+#define DEFAULT_SOCKET_PATH "/daemon-socket/socket"
 
 
 Path readStorePath(Source & from);

src/nix-worker/nix-worker.cc

@@ -753,6 +753,8 @@ static void daemonLoop()
 
     string socketPath = nixStateDir + DEFAULT_SOCKET_PATH;
 
+    createDirs(dirOf(socketPath));
+
     struct sockaddr_un addr;
     addr.sun_family = AF_UNIX;
     if (socketPath.size() >= sizeof(addr.sun_path))
@@ -762,7 +764,8 @@ static void daemonLoop()
     unlink(socketPath.c_str());
 
     /* Make sure that the socket is created with 0666 permission
-       (everybody can connect). */
+       (everybody can connect --- provided they have access to the
+       directory containing the socket). */
     mode_t oldMode = umask(0111);
     int res = bind(fdSocket, (struct sockaddr *) &addr, sizeof(addr));
     umask(oldMode);

tests/fixed.nix.in

@@ -41,8 +41,8 @@ rec {
   # Test for building two derivations in parallel that produce the
   # same output path because they're fixed-output derivations.
   parallelSame = [
-    (f2 "foo" ./fixed.builder2.sh "flat" "md5" "3670af73070fa14077ad74e0f5ea4e42")
+    (f2 "foo" ./fixed.builder2.sh "recursive" "md5" "3670af73070fa14077ad74e0f5ea4e42")
-    (f2 "bar" ./fixed.builder2.sh "flat" "md5" "3670af73070fa14077ad74e0f5ea4e42")
+    (f2 "bar" ./fixed.builder2.sh "recursive" "md5" "3670af73070fa14077ad74e0f5ea4e42")
   ];
 
-}
+}