* Revert r19797, and use a simpler solution: just don't monitor build

hooks for silence.  It's unnecessary because the remote nix-store
  command is already monitoring the real build.

src/libmain/shared.cc

@@ -31,11 +31,6 @@ static void sigintHandler(int signo)
 }
 
 
-static void sigalrmHandler(int signo)
-{
-}
-
-
 Path makeRootName(const Path & gcRoot, int & counter)
 {
     counter++;
@@ -165,14 +160,6 @@ static void initAndRun(int argc, char * * argv)
     if (sigaction(SIGPIPE, &act, 0))
         throw SysError("ignoring SIGPIPE");
 
-    /* Catch SIGALRM with an empty handler (we just need it to get an
-       EINTR from blocking system calls). */
-    act.sa_handler = sigalrmHandler;
-    sigfillset(&act.sa_mask);
-    act.sa_flags = 0;
-    if (sigaction(SIGALRM, &act, 0))
-        throw SysError("installing handler for SIGALRM");
-
     /* Reset SIGCHLD to its default. */
     act.sa_handler = SIG_DFL;
     act.sa_flags = 0;

src/libstore/build.cc

@@ -162,6 +162,7 @@ struct Child
 {
     WeakGoalPtr goal;
     set<int> fds;
+    bool monitorForSilence;
     bool inBuildSlot;
     time_t lastOutput; /* time we last got output on stdout/stderr */
 };
@@ -234,7 +235,7 @@ public:
     /* Registers a running child process.  `inBuildSlot' means that
        the process counts towards the jobs limit. */
     void childStarted(GoalPtr goal, pid_t pid,
-        const set<int> & fds, bool inBuildSlot);
+        const set<int> & fds, bool inBuildSlot, bool monitorForSilence);
 
     /* Unregisters a running child process.  `wakeSleepers' should be
        false if there is no sense in waking up goals that are sleeping
@@ -1262,7 +1263,7 @@ DerivationGoal::HookReply DerivationGoal::tryBuildHook()
     pid.setKillSignal(SIGTERM);
     logPipe.writeSide.close();
     worker.childStarted(shared_from_this(),
-        pid, singleton<set<int> >(logPipe.readSide), false);
+        pid, singleton<set<int> >(logPipe.readSide), false, false);
 
     toHook.readSide.close();
 
@@ -1767,7 +1768,7 @@ void DerivationGoal::startBuilder()
     pid.setSeparatePG(true);
     logPipe.writeSide.close();
     worker.childStarted(shared_from_this(), pid,
-        singleton<set<int> >(logPipe.readSide), true);
+        singleton<set<int> >(logPipe.readSide), true, true);
 
     if (printBuildTrace) {
         printMsg(lvlError, format("@ build-started %1% %2% %3% %4%")
@@ -2274,7 +2275,7 @@ void SubstitutionGoal::tryToRun()
     pid.setKillSignal(SIGTERM);
     logPipe.writeSide.close();
     worker.childStarted(shared_from_this(),
-        pid, singleton<set<int> >(logPipe.readSide), true);
+        pid, singleton<set<int> >(logPipe.readSide), true, true);
 
     state = &SubstitutionGoal::finished;
 
@@ -2474,13 +2475,15 @@ unsigned Worker::getNrLocalBuilds()
 
 
 void Worker::childStarted(GoalPtr goal,
-    pid_t pid, const set<int> & fds, bool inBuildSlot)
+    pid_t pid, const set<int> & fds, bool inBuildSlot,
+    bool monitorForSilence)
 {
     Child child;
     child.goal = goal;
     child.fds = fds;
     child.lastOutput = time(0);
     child.inBuildSlot = inBuildSlot;
+    child.monitorForSilence = monitorForSilence;
     children[pid] = child;
     if (inBuildSlot) nrLocalBuilds++;
 }
@@ -2601,13 +2604,17 @@ void Worker::waitForInput()
     if (maxSilentTime != 0) {
         time_t oldest = 0;
         foreach (Children::iterator, i, children) {
+            if (i->second.monitorForSilence) {
                 oldest = oldest == 0 || i->second.lastOutput < oldest
                     ? i->second.lastOutput : oldest;
             }
+        }
+        if (oldest) {
             useTimeout = true;
             timeout.tv_sec = std::max((time_t) 0, oldest + maxSilentTime - before);
             printMsg(lvlVomit, format("sleeping %1% seconds") % timeout.tv_sec);
         }
+    }
 
     /* If we are polling goals that are waiting for a lock, then wake
        up after a few seconds at most. */
@@ -2681,6 +2688,7 @@ void Worker::waitForInput()
         }
 
         if (maxSilentTime != 0 &&
+            j->second.monitorForSilence &&
             after - j->second.lastOutput >= (time_t) maxSilentTime)
         {
             printMsg(lvlError,

src/libstore/pathlocks.cc

@@ -37,8 +37,7 @@ void deleteLockFile(const Path & path, int fd)
 }
 
 
-bool lockFile(int fd, LockType lockType, bool wait,
-    unsigned int progressInterval)
+bool lockFile(int fd, LockType lockType, bool wait)
 {
     struct flock lock;
     if (lockType == ltRead) lock.l_type = F_RDLCK;
@@ -50,20 +49,11 @@ bool lockFile(int fd, LockType lockType, bool wait,
     lock.l_len = 0; /* entire file */
 
     if (wait) {
-        /* Wait until we acquire the lock.  If `progressInterval' is
-           non-zero, when print a message every `progressInterval'
-           seconds.  This is mostly to make sure that remote builders
-           aren't killed due to the `max-silent-time' inactivity
-           monitor while waiting for the garbage collector lock. */
-        while (1) {
-            if (progressInterval) alarm(progressInterval);
-            if (fcntl(fd, F_SETLKW, &lock) == 0) break;
+        while (fcntl(fd, F_SETLKW, &lock) != 0) {
             checkInterrupt();
             if (errno != EINTR)
                 throw SysError(format("acquiring/releasing lock"));
-            if (progressInterval) printMsg(lvlError, "still waiting for lock...");
         }
-        alarm(0);
     } else {
         while (fcntl(fd, F_SETLK, &lock) != 0) {
             checkInterrupt();

src/libstore/pathlocks.hh

@@ -17,8 +17,7 @@ void deleteLockFile(const Path & path, int fd);
 
 enum LockType { ltRead, ltWrite, ltNone };
 
-bool lockFile(int fd, LockType lockType, bool wait,
-    unsigned int progressInterval = 300);
+bool lockFile(int fd, LockType lockType, bool wait);
 
 
 class PathLocks