1 files changed, 93 insertions, 0 deletions
diff --git a/src/tui/mailbox.cc b/src/tui/mailbox.cc
new file mode 100644
index 0000000..89e2c19
--- /dev/null
+++ b/src/tui/mailbox.cc
@@ -0,0 +1,93 @@
+/*
+ * Ricochet - A minimalist CLI web browser for fast, distraction-free navigation.
+ * Copyright (C) 2026  Richard Qin
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "mailbox.hh"
+
+#include <algorithm>
+#include <cerrno>
+#include <sys/eventfd.h>
+#include <system_error>
+#include <unistd.h>
+#include <utility>
+
+namespace ricochet::tui::detail {
+
+Mailbox::Mailbox() : event_fd_( eventfd( 0, EFD_CLOEXEC | EFD_NONBLOCK ) )
+{
+  if ( event_fd_ == -1 ) {
+    throw std::system_error( errno, std::generic_category(), "eventfd" );
+  }
+}
+
+Mailbox::~Mailbox()
+{ ::close( event_fd_ ); }
+
+PostResult Mailbox::post( HostUpdate update )
+{
+  const std::lock_guard lock( mutex_ );
+  // Closing rejects later producers while existing sender handles remain alive.
+  if ( closed_ ) {
+    return PostResult::Closed;
+  }
+  updates_.push_back( std::move( update ) );
+  int result;
+  do {
+    result = eventfd_write( event_fd_, 1 );
+  } while ( result == -1 && errno == EINTR );
+  // EAGAIN means the counter is already readable, so the loop is already awake.
+  if ( result == -1 && errno != EAGAIN ) {
+    const int error = errno;
+    updates_.pop_back();
+    throw std::system_error( error, std::generic_category(), "eventfd_write" );
+  }
+  return PostResult::Queued;
+}
+
+std::vector<HostUpdate> Mailbox::take( std::size_t limit )
+{
+  const std::lock_guard lock( mutex_ );
+  eventfd_t counter {};
+  int result;
+  do {
+    result = eventfd_read( event_fd_, &counter );
+  } while ( result == -1 && errno == EINTR );
+  // An empty queue has no wake token. Other read errors are transport failures.
+  if ( result == -1 && errno != EAGAIN ) {
+    throw std::system_error( errno, std::generic_category(), "eventfd_read" );
+  }
+  const auto count = std::min( limit, updates_.size() );
+  std::vector<HostUpdate> batch;
+  batch.reserve( count );
+  for ( std::size_t i = 0; i < count; ++i ) {
+    batch.push_back( std::move( updates_.front() ) );
+    updates_.pop_front();
+  }
+  return batch;
+}
+
+int Mailbox::descriptor() const noexcept
+{ return event_fd_; }
+
+void Mailbox::close() noexcept
+{
+  const std::lock_guard lock( mutex_ );
+  closed_ = true;
+  updates_.clear();
+}
+
+} // namespace ricochet::tui::detail