util: Fix multiple use of LockDirectory This commit fixes problems wi…

…th calling LockDirectory multiple times on the same directory, or from multiple threads. It also fixes the build on OpenBSD.

src/util/system.cpp

@@ -107,18 +107,32 @@ bool CheckDiskSpace(const fs::path& dir, uint64_t additional_bytes)
 
 bool LockDirectory(const fs::path& directory, const std::string& lockfile_name, bool probe_only)
 {
+    // A map that contains all the currently held directory locks. After
+    // successful locking, these will be held here until the global
+    // destructor cleans them up and thus automatically unlocks them.
+    static std::map<std::string, std::unique_ptr<boost::interprocess::file_lock>> locks;
+    // Protect the map with a mutex
+    static std::mutex cs;
+    std::lock_guard<std::mutex> ulock(cs);
     fs::path pathLockFile = directory / lockfile_name;
-    FILE* file = fsbridge::fopen(pathLockFile, "a"); // empty lock file; created if it doesn't exist.
+
+    // If a lock for this directory already exists in the map, don't try to re-lock it
+    if (locks.count(pathLockFile.string())) {
+        return true;
+    }
+
+    // Create empty lock file if it doesn't exist.
+    FILE* file = fsbridge::fopen(pathLockFile, "a");
     if (file) fclose(file);
 
     try {
-        static std::map<std::string, boost::interprocess::file_lock> locks;
-        boost::interprocess::file_lock& lock = locks.emplace(pathLockFile.string(), pathLockFile.string().c_str()).first->second;
-        if (!lock.try_lock()) {
+        auto lock = std::make_unique<boost::interprocess::file_lock>(pathLockFile.string().c_str());
+        if (!lock->try_lock()) {
             return false;
         }
-        if (probe_only) {
-            lock.unlock();
+        if (!probe_only) {
+            // Lock successful and we're not just probing, put it into the map
+            locks.emplace(pathLockFile.string(), std::move(lock));
         }
     } catch (const boost::interprocess::interprocess_exception& e) {
         return error("Error while attempting to lock directory %s: %s", directory.string(), e.what());