[LLDB][NFC] Fix memory/resource leak in FifoFiles

[fixathon]

Summary

The original code is creating a future object on the heap, but does not delete it in one of the return paths causing a leak.
Because the lifetime of the future object is the local scope of its containing function, there's no need for heap-based allocation in the first place.
This diff fixes the memory leak by moving the future object allocation to stack-based RAII. There's no change to the functionality or style of the code.

[clayborg]

lldb/tools/lldb-vscode/FifoFiles.cpp

53–54

This comment seems to indicate we need to use a pointer. Seems like this should either be rewritten to not try to use a future with a timeout or left as is?

[fixathon]

lldb/tools/lldb-vscode/FifoFiles.cpp

53–54

Good catch. Looks like the original code aims to intentionally orphan the 'future' object if it's blocked (possibly infinitely) in its destructor waiting for the executing thread to rejoin. This could happen if the workload uses blocking I/O calls like we have here.

lldb/tools/lldb-vscode/FifoFiles.cpp

#else
   return std::make_shared<FifoFile>(path);
 #endif
 }
 
 FifoFileIO::FifoFileIO(StringRef fifo_file, StringRef other_endpoint_name)
     : m_fifo_file(fifo_file), m_other_endpoint_name(other_endpoint_name) {}
 
 Expected<json::Value> FifoFileIO::ReadJSON(std::chrono::milliseconds timeout) {
   // We use a pointer for this future, because otherwise its normal destructor
   // would wait for the getline to end, rendering the timeout useless.
   Optional<std::string> line;
-  std::future<void> *future =
-      new std::future<void>(std::async(std::launch::async, [&]() {
-        std::ifstream reader(m_fifo_file, std::ifstream::in);
-        std::string buffer;
-        std::getline(reader, buffer);
-        if (!buffer.empty())
-          line = buffer;
-      }));
-  if (future->wait_for(timeout) == std::future_status::timeout || !line)
+  std::future<void> future = std::async(std::launch::async, [&]() {
+  });
+  if (future.wait_for(timeout) == std::future_status::timeout || !line)
     return createStringError(inconvertibleErrorCode(),
                              "Timed out trying to get messages from the " +
                                  m_other_endpoint_name);
-  delete future;
+
   return json::parse(*line);
 }
 
 Error FifoFileIO::SendJSON(const json::Value &json,
                            std::chrono::milliseconds timeout) {
   bool done = false;
-  std::future<void> *future =
-      new std::future<void>(std::async(std::launch::async, [&]() {
-        std::ofstream writer(m_fifo_file, std::ofstream::out);
-        writer << JSONToString(json) << std::endl;
-        done = true;
-      }));
-  if (future->wait_for(timeout) == std::future_status::timeout || !done) {
+  std::future<void> future = std::async(std::launch::async, [&]() {
+  });
+  if (future.wait_for(timeout) == std::future_status::timeout || !done) {
     return createStringError(inconvertibleErrorCode(),
                              "Timed out trying to send messages to the " +
                                  m_other_endpoint_name);
   }
-  delete future;
   return Error::success();
 }
 
 } // namespace lldb_vscode