[llvm] [Support] Prevent leaking unique lock files (PR #130984)

[Jan Svoboda via llvm-commits]

https://github.com/jansvoboda11 created https://github.com/llvm/llvm-project/pull/130984

Prior to this PR, failing to get the host ID would leave the unique lock file on the file system. This is now fixed by constructing `RemoveUniqueLockFileOnSignal` earlier. This PR also removes one call to `sys::fs::remove()` that is now redundant and another that was redundant even before this patch.

>From 1c7201fcf4045b60b4b759445bba03307a41aff3 Mon Sep 17 00:00:00 2001
From: Jan Svoboda <jan_svoboda at apple.com>
Date: Tue, 11 Mar 2025 16:09:31 -0700
Subject: [PATCH] [Support] Prevent leaking unique lock files

Prior to this PR, failing to get the host ID would leave the unique lock file on the file system. This is now fixed by constructing `RemoveUniqueLockFileOnSignal` earlier. This PR also removes one call to `sys::fs::remove()` that is now redundant and another that was redundant even before this patch.
---
 llvm/lib/Support/LockFileManager.cpp | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/llvm/lib/Support/LockFileManager.cpp b/llvm/lib/Support/LockFileManager.cpp
index 7cf9db379974f..430dc1fa25fef 100644
--- a/llvm/lib/Support/LockFileManager.cpp
+++ b/llvm/lib/Support/LockFileManager.cpp
@@ -189,6 +189,10 @@ Expected<bool> LockFileManager::tryLock() {
     return createStringError(EC, "failed to create unique file " +
                                      UniqueLockFileName);
 
+  // Clean up the unique file on signal or scope exit. This also releases the
+  // lock if it's held since the .lock symlink will point to a nonexistent file.
+  RemoveUniqueLockFileOnSignal RemoveUniqueFile(UniqueLockFileName);
+
   // Write our process ID to our unique lock file.
   {
     SmallString<256> HostID;
@@ -200,21 +204,15 @@ Expected<bool> LockFileManager::tryLock() {
     Out.close();
 
     if (Out.has_error()) {
-      // We failed to write out PID, so report the error, remove the
-      // unique lock file, and fail.
+      // We failed to write out PID, so report the error and fail.
       Error Err = createStringError(Out.error(),
                                     "failed to write to " + UniqueLockFileName);
-      sys::fs::remove(UniqueLockFileName);
       // Don't call report_fatal_error.
       Out.clear_error();
       return std::move(Err);
     }
   }
 
-  // Clean up the unique file on signal, which also releases the lock if it is
-  // held since the .lock symlink will point to a nonexistent file.
-  RemoveUniqueLockFileOnSignal RemoveUniqueFile(UniqueLockFileName);
-
   while (true) {
     // Create a link from the lock file name. If this succeeds, we're done.
     std::error_code EC =
@@ -232,8 +230,6 @@ Expected<bool> LockFileManager::tryLock() {
     // Someone else managed to create the lock file first. Read the process ID
     // from the lock file.
     if (auto LockFileOwner = readLockFile(LockFileName)) {
-      // Wipe out our unique lock file (it's useless now)
-      sys::fs::remove(UniqueLockFileName);
       Owner = std::move(*LockFileOwner);
       return false;
     }