* In `nix-env -i|-u|-e', lock the profile to prevent races between

  concurrent nix-env operations on the same profile.  Fixes NIX-7.

2 files changed, 11 insertions, 6 deletions

diff --git a/src/libstore/pathlocks.cc b/src/libstore/pathlocks.cc
index 3beb49aac803..7f7cbdf15a68 100644
--- a/src/libstore/pathlocks.cc
+++ b/src/libstore/pathlocks.cc
@@ -51,14 +51,14 @@ PathLocks::PathLocks()
 }
 
 
-PathLocks::PathLocks(const PathSet & paths)
+PathLocks::PathLocks(const PathSet & paths, const string & waitMsg)
     : deletePaths(false)
 {
-    lockPaths(paths);
+    lockPaths(paths, waitMsg);
 }
 
 
-void PathLocks::lockPaths(const PathSet & _paths)
+void PathLocks::lockPaths(const PathSet & _paths, const string & waitMsg)
 {
     /* May be called only once! */
     assert(fds.empty());
@@ -94,7 +94,10 @@ void PathLocks::lockPaths(const PathSet & _paths)
                 throw SysError(format("opening lock file `%1%'") % lockPath);
 
             /* Acquire an exclusive lock. */
-            lockFile(fd, ltWrite, true);
+            if (!lockFile(fd, ltWrite, false)) {
+                if (waitMsg != "") printMsg(lvlError, waitMsg);
+                lockFile(fd, ltWrite, true);
+            }
 
             debug(format("lock acquired on `%1%'") % lockPath);
 
diff --git a/src/libstore/pathlocks.hh b/src/libstore/pathlocks.hh
index 42ebe58df691..2fd0e0d1ed52 100644
--- a/src/libstore/pathlocks.hh
+++ b/src/libstore/pathlocks.hh
@@ -18,8 +18,10 @@ private:
 
 public:
     PathLocks();
-    PathLocks(const PathSet & paths);
-    void lockPaths(const PathSet & _paths);
+    PathLocks(const PathSet & paths,
+        const string & waitMsg = "");
+    void lockPaths(const PathSet & _paths,
+        const string & waitMsg = "");
     ~PathLocks();
     void setDeletion(bool deletePaths);
 };