* Start of concurrent garbage collection. Processes write temporary

  roots to a per-process temporary file in /nix/var/nix/temproots
  while holding a write lock on that file.  The garbage collector
  acquires read locks on all those files, thus blocking further
  progress in other Nix processes, and reads the sets of temporary
  roots.

2 files changed, 12 insertions, 4 deletions

diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 0af6ee149bae..611567c12b1b 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -234,8 +234,8 @@ Path createTempDir()
 
 void writeStringToFile(const Path & path, const string & s)
 {
-    AutoCloseFD fd = open(path.c_str(),
-        O_CREAT | O_EXCL | O_WRONLY, 0666);
+    AutoCloseFD fd(open(path.c_str(),
+        O_CREAT | O_EXCL | O_WRONLY, 0666));
     if (fd == -1)
         throw SysError(format("creating file `%1%'") % path);
     writeFull(fd, (unsigned char *) s.c_str(), s.size());
@@ -375,6 +375,12 @@ AutoCloseFD::AutoCloseFD(int fd)
 }
 
 
+AutoCloseFD::AutoCloseFD(const AutoCloseFD & fd)
+{
+    abort();
+}
+
+
 AutoCloseFD::~AutoCloseFD()
 {
     try {
@@ -392,7 +398,7 @@ void AutoCloseFD::operator =(int fd)
 }
 
 
-AutoCloseFD::operator int()
+AutoCloseFD::operator int() const
 {
     return fd;
 }
@@ -401,6 +407,7 @@ AutoCloseFD::operator int()
 void AutoCloseFD::close()
 {
     if (fd != -1) {
+        debug(format("closing fd %1%") % fd);
         if (::close(fd) == -1)
             /* This should never happen. */
             throw SysError("closing file descriptor");
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index d947c34252a7..104e3f2651b4 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -179,9 +179,10 @@ class AutoCloseFD
 public:
     AutoCloseFD();
     AutoCloseFD(int fd);
+    AutoCloseFD(const AutoCloseFD & fd);
     ~AutoCloseFD();
     void operator =(int fd);
-    operator int();
+    operator int() const;
     void close();
     bool isOpen();
     int borrow();