[lld] r317631 - Simplify unlinkAsync.

[Rafael Espindola via llvm-commits]

Author: rafael
Date: Tue Nov  7 15:01:37 2017
New Revision: 317631

URL: http://llvm.org/viewvc/llvm-project?rev=317631&view=rev
Log:
Simplify unlinkAsync.

It used to rename the file before removing it in a background thread.

A simpler way to delay the removal is simply to open the file.

Since this is a posix specific issue, simplify the windows
implementation.

Modified:
    lld/trunk/ELF/Filesystem.cpp

Modified: lld/trunk/ELF/Filesystem.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Filesystem.cpp?rev=317631&r1=317630&r2=317631&view=diff
==============================================================================
--- lld/trunk/ELF/Filesystem.cpp (original)
+++ lld/trunk/ELF/Filesystem.cpp Tue Nov  7 15:01:37 2017
@@ -14,8 +14,12 @@
 #include "Filesystem.h"
 #include "Config.h"
 #include "lld/Common/Threads.h"
+#include "llvm/Config/config.h"
 #include "llvm/Support/FileOutputBuffer.h"
 #include "llvm/Support/FileSystem.h"
+#if defined(HAVE_UNISTD_H)
+#include <unistd.h>
+#endif
 
 using namespace llvm;
 
@@ -35,27 +39,30 @@ using namespace lld::elf;
 // Since LLD can link a 1 GB binary in about 5 seconds, that waste
 // actually counts.
 //
-// This function spawns a background thread to call unlink.
+// This function spawns a background thread to remove the file.
 // The calling thread returns almost immediately.
 void elf::unlinkAsync(StringRef Path) {
+// Removing a file is async on windows.
+#if defined(LLVM_ON_WIN32)
+  sys::fs::remove(Path);
+#else
   if (!ThreadsEnabled || !sys::fs::exists(Path) ||
       !sys::fs::is_regular_file(Path))
     return;
 
-  // First, rename Path to avoid race condition. We cannot remove
-  // Path from a different thread because we are now going to create
-  // Path as a new file. If we do that in a different thread, the new
-  // thread can remove the new file.
-  SmallString<128> TempPath;
-  if (sys::fs::createUniqueFile(Path + "tmp%%%%%%%%", TempPath))
+  // We cannot just remove path from a different thread because we are now going
+  // to create path as a new file.
+  // Instead we open the file and unlink it on this thread. The unlink is fast
+  // since the open fd guarantees that it is not removing the last reference.
+  int FD;
+  if (std::error_code EC = sys::fs::openFileForRead(Path, FD))
     return;
-  if (sys::fs::rename(Path, TempPath)) {
-    sys::fs::remove(TempPath);
-    return;
-  }
 
-  // Remove TempPath in background.
-  runBackground([=] { ::remove(TempPath.str().str().c_str()); });
+  sys::fs::remove(Path);
+
+  // close and therefore remove TempPath in background.
+  runBackground([=] { ::close(FD); });
+#endif
 }
 
 // Simulate file creation to see if Path is writable.