Reapply "Use gethostuuid() on Mac to identify hosts for LockFileManager"

Reapplies r241005 after fixing the build on non-Mac platforms. Original
commit message below.

The hostname can be very unstable when there are many machines on the
network competing for the same name. Using the hardware UUID makes it
less likely to have collisions or to consider files written by the
current host to be owned by a different one at a later time.

rdar://problem/21512307

llvm-svn: 241012

lib/Support/LockFileManager.cpp

@@ -21,6 +21,16 @@
 #if LLVM_ON_UNIX
 #include <unistd.h>
 #endif
+
+#if defined(__APPLE__) && defined(__MAC_OS_X_VERSION_MIN_REQUIRED) && (__MAC_OS_X_VERSION_MIN_REQUIRED > 1050)
+#define USE_OSX_GETHOSTUUID 1
+#else
+#define USE_OSX_GETHOSTUUID 0
+#endif
+
+#if USE_OSX_GETHOSTUUID
+#include <uuid/uuid.h>
+#endif
 using namespace llvm;
 
 /// \brief Attempt to read the lock file with the given name, if it exists.
@@ -56,14 +66,45 @@ LockFileManager::readLockFile(StringRef LockFileName) {
   return None;
 }
 
-bool LockFileManager::processStillExecuting(StringRef Hostname, int PID) {
+static std::error_code getHostID(SmallVectorImpl<char> &HostID) {
+  HostID.clear();
+
+#if USE_OSX_GETHOSTUUID
+  // On OS X, use the more stable hardware UUID instead of hostname.
+  struct timespec wait = {1, 0}; // 1 second.
+  uuid_t uuid;
+  if (gethostuuid(uuid, &wait) != 0)
+    return std::error_code(errno, std::system_category());
+
+  uuid_string_t UUIDStr;
+  uuid_unparse(uuid, UUIDStr);
+  StringRef UUIDRef(UUIDStr);
+  HostID.append(UUIDRef.begin(), UUIDRef.end());
+
+#elif LLVM_ON_UNIX
+  char HostName[256];
+  HostName[255] = 0;
+  HostName[0] = 0;
+  gethostname(HostName, 255);
+  StringRef HostNameRef(HostName);
+  HostID.append(HostNameRef.begin(), HostNameRef.end());
+
+#else
+  StringRef Dummy("localhost");
+  HostID.append(Dummy.begin(), Dummy.end());
+#endif
+
+  return std::error_code();
+}
+
+bool LockFileManager::processStillExecuting(StringRef HostID, int PID) {
 #if LLVM_ON_UNIX && !defined(__ANDROID__)
-  char MyHostname[256];
-  MyHostname[255] = 0;
-  MyHostname[0] = 0;
-  gethostname(MyHostname, 255);
+  SmallString<256> StoredHostID;
+  if (getHostID(StoredHostID))
+    return true; // Conservatively assume it's executing on error.
+
   // Check whether the process is dead. If so, we're done.
-  if (MyHostname == Hostname && getsid(PID) == -1 && errno == ESRCH)
+  if (StoredHostID == HostID && getsid(PID) == -1 && errno == ESRCH)
     return false;
 #endif
 
@@ -126,17 +167,18 @@ LockFileManager::LockFileManager(StringRef FileName)
 
   // Write our process ID to our unique lock file.
   {
-    raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true);
+    SmallString<256> HostID;
+    if (auto EC = getHostID(HostID)) {
+      Error = EC;
+      return;
+    }
 
+    raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true);
+    Out << HostID << ' ';
 #if LLVM_ON_UNIX
-    // FIXME: move getpid() call into LLVM
-    char hostname[256];
-    hostname[255] = 0;
-    hostname[0] = 0;
-    gethostname(hostname, 255);
-    Out << hostname << ' ' << getpid();
+    Out << getpid();
 #else
-    Out << "localhost 1";
+    Out << "1";
 #endif
     Out.close();