Fix parallel deletion (#1858)

Author: franzpoeschel

include/openPMD/auxiliary/Filesystem.hpp

@@ -20,6 +20,7 @@
  */
 #pragma once
 
+#include <optional>
 #include <string>
 #include <vector>
 
@@ -66,6 +67,19 @@ namespace auxiliary
      */
     std::vector<std::string> list_directory(std::string const &path);
 
+    /** List all contents of a directory at a given absolute or relative path.
+     *
+     * @note    The equivalent of `ls path`
+     * @note    Both contained files and directories are listed.
+     *          `.` and `..` are not returned.
+     * @param   path    Absolute or relative path of directory to examine.
+     * @return  Vector of all contained files and directories,
+     *          or an empty option in case of an IO error, in which case the
+     *          specific error will be stored in errno.
+     */
+    std::optional<std::vector<std::string>>
+    list_directory_nothrow(std::string const &path);
+
     /** Create all required directories to have a reachable given absolute or
      * relative path.
      *

src/auxiliary/Filesystem.cpp

@@ -67,6 +67,20 @@ bool file_exists(std::string const &path)
 }
 
 std::vector<std::string> list_directory(std::string const &path)
+{
+    auto res = list_directory_nothrow(path);
+    if (!res)
+    {
+        throw std::system_error(std::error_code(errno, std::system_category()));
+    }
+    else
+    {
+        return *res;
+    }
+}
+
+std::optional<std::vector<std::string>>
+list_directory_nothrow(std::string const &path)
 {
     std::vector<std::string> ret;
 #ifdef _WIN32
@@ -86,7 +100,9 @@ std::vector<std::string> list_directory(std::string const &path)
 #else
     auto directory = opendir(path.c_str());
     if (!directory)
-        throw std::system_error(std::error_code(errno, std::system_category()));
+    {
+        return std::nullopt;
+    }
     dirent *entry;
     while ((entry = readdir(directory)) != nullptr)
         if (strcmp(entry->d_name, ".") != 0 && strcmp(entry->d_name, "..") != 0)
@@ -150,14 +166,20 @@ bool remove_directory(std::string const &path)
         return (0 == remove(p.c_str()));
     };
 #endif
-    for (auto const &entry : list_directory(path))
+    auto entries = list_directory_nothrow(path);
+    // Check if some other process was faster deleting this
+    if (entries)
     {
-        auto partialPath = path;
-        partialPath.append(std::string(1, directory_separator)).append(entry);
-        if (directory_exists(partialPath))
-            success &= remove_directory(partialPath);
-        else if (file_exists(partialPath))
-            success &= remove_file(partialPath);
+        for (auto const &entry : *entries)
+        {
+            auto partialPath = path;
+            partialPath.append(std::string(1, directory_separator))
+                .append(entry);
+            if (directory_exists(partialPath))
+                success &= remove_directory(partialPath);
+            else if (file_exists(partialPath))
+                success &= remove_file(partialPath);
+        }
     }
     success &= del(path);
     return success;