From e450b7aeb3f4790627cd0d3d717b74037dbee3ff Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@meta.com>
Date: Mon, 25 Dec 2023 08:39:14 -0800
Subject: [PATCH] Implement locking

---
 test/scan-test.cc | 29 +++++++++++++++++++++++++++++
 test/scan.h       | 22 +++++++++++++++++++---
 2 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/test/scan-test.cc b/test/scan-test.cc
index 5d6585ef..e8fd75e5 100644
--- a/test/scan-test.cc
+++ b/test/scan-test.cc
@@ -144,4 +144,33 @@ TEST(scan_test, file) {
   EXPECT_EQ(n1, 10);
   EXPECT_EQ(n2, 20);
 }
+
+TEST(scan_test, lock) {
+  fmt::file read_end, write_end;
+  fmt::file::pipe(read_end, write_end);
+
+  std::thread producer([&]() {
+    fmt::string_view input = "42 ";
+    for (int i = 0; i < 1000; ++i)
+      write_end.write(input.data(), input.size());
+    write_end.close();
+  });
+
+  fmt::buffered_file f = read_end.fdopen("r");
+  auto fun = [&]() {
+    int value = 0;
+    while (fmt::scan(f.get(), "{}", value)) {
+      if (value != 42) {
+        read_end.close();
+        EXPECT_EQ(value, 42);
+        break;
+      }
+    }
+  };
+  std::thread consumer1(fun);
+  std::thread consumer2(fun);
+  producer.join();
+  consumer1.join();
+  consumer2.join();
+}
 #endif  // FMT_USE_FCNTL
diff --git a/test/scan.h b/test/scan.h
index 3032b7bb..ea7c51ba 100644
--- a/test/scan.h
+++ b/test/scan.h
@@ -266,9 +266,20 @@ class file_scan_buffer : public scan_buffer {
  public:
   explicit file_scan_buffer(FILE* f)
       : scan_buffer(nullptr, nullptr, false), file_(f) {
-    // TODO: lock file?
+#ifndef _WIN32
+    flockfile(f);
+#else
+    _lock_file(f);
+#endif
     fill();
   }
+  ~file_scan_buffer() {
+#ifndef _WIN32
+    funlockfile(file_);
+#else
+    _unlock_file(file_);
+#endif
+  }
 };
 }  // namespace detail
 
@@ -472,7 +483,6 @@ struct scan_handler : error_handler {
     switch (arg_.type) {
     case scan_type::int_type:
       if (auto value = read_int()) *arg_.int_value = *value;
-      // TODO: stop on end of input
       break;
     case scan_type::uint_type:
       if (auto value = read_uint()) *arg_.uint_value = *value;
@@ -512,6 +522,11 @@ struct scan_handler : error_handler {
     arg_.custom.scan(arg_.custom.value, parse_ctx_, scan_ctx_);
     return parse_ctx_.begin();
   }
+
+  void on_error(const char* message) {
+    scan_ctx_.advance_to(scan_ctx_.end());
+    error_handler::on_error(message);
+  }
 };
 }  // namespace detail
 
@@ -533,9 +548,10 @@ auto scan(string_view input, string_view fmt, T&... args)
   return input.begin() + (buf.begin().base() - input.data());
 }
 
-template <typename... T> void scan(std::FILE* f, string_view fmt, T&... args) {
+template <typename... T> bool scan(std::FILE* f, string_view fmt, T&... args) {
   auto&& buf = detail::file_scan_buffer(f);
   vscan(buf, fmt, make_scan_args(args...));
+  return buf.begin() != buf.end();
 }
 
 FMT_END_NAMESPACE