From 979ee07c675dad56446ac1f36f9d43a35fe90949 Mon Sep 17 00:00:00 2001
From: Trevor Shoe <trevor.schupbach@canonical.com>
Date: Fri, 6 Dec 2024 12:19:22 -0500
Subject: [PATCH] [sshfs] Use seperate signaling thread

---
 src/platform/platform_unix.cpp   | 48 +++++++++++++++++++-------------
 src/sshfs_mount/sshfs_server.cpp |  2 +-
 2 files changed, 30 insertions(+), 20 deletions(-)

diff --git a/src/platform/platform_unix.cpp b/src/platform/platform_unix.cpp
index 895e0d4cf1..59708b6de6 100644
--- a/src/platform/platform_unix.cpp
+++ b/src/platform/platform_unix.cpp
@@ -26,6 +26,7 @@
 #include <unistd.h>
 
 #include <libssh/sftp.h>
+#include <multipass/auto_join_thread.h>
 
 namespace mp = multipass;
 
@@ -183,37 +184,46 @@ timespec make_timespec(std::chrono::duration<Rep, Period> duration)
     return timespec{seconds.count(), std::chrono::duration_cast<std::chrono::nanoseconds>(duration - seconds).count()};
 }
 
+#include <iostream>
+
 std::function<std::optional<int>(const std::function<bool()>&)> mp::platform::make_quit_watchdog(
     const std::chrono::milliseconds& timeout)
 {
     return [sigset = make_and_block_signals({SIGQUIT, SIGTERM, SIGHUP, SIGUSR2}),
-            time = make_timespec(timeout)](const std::function<bool()>& condition) -> std::optional<int> {
-        // create a timer to send SIGUSR2 which unblocks this thread
-        sigevent sevp{};
-        sevp.sigev_notify = SIGEV_SIGNAL;
-        sevp.sigev_signo = SIGUSR2;
-
-        timer_t timer{};
-        if (timer_create(CLOCK_MONOTONIC, &sevp, &timer) == -1)
-            throw std::runtime_error(fmt::format("Could not create timer: {}", strerror(errno)));
+            timeout](const std::function<bool()>& condition) -> std::optional<int> {
+        std::mutex sig_mtx;
+        std::condition_variable sig_cv;
+        int sig = SIGUSR2;
 
-        // scope guard to make sure the timer is deleted once it's no longer needed
-        const auto timer_guard = sg::make_scope_guard([timer]() noexcept { timer_delete(timer); });
+        // A signal generator that triggers after `timeout`
+        AutoJoinThread signaler([&sig_mtx, &sig_cv, &sig, &timeout, signalee = pthread_self()] {
+            std::unique_lock lock(sig_mtx);
+            while (sig == SIGUSR2)
+            {
+                auto status = sig_cv.wait_for(lock, timeout);
 
-        // set timer interval and initial time to provided timeout
-        const itimerspec timer_interval{time, time};
-        if (timer_settime(timer, 0, &timer_interval, nullptr) == -1)
-            throw std::runtime_error(fmt::format("Could not set timer: {}", strerror(errno)));
+                if (sig == SIGUSR2 && status == std::cv_status::timeout)
+                {
+                    pthread_kill(signalee, SIGUSR2);
+                }
+            }
+        });
 
         // wait on signals and condition
-        int sig = SIGUSR2;
-        while (sig == SIGUSR2 && condition())
+        int ret = SIGUSR2;
+        while (ret == SIGUSR2 && condition())
         {
             // can't use sigtimedwait since macOS doesn't support it
-            sigwait(&sigset, &sig);
+            sigwait(&sigset, &ret);
+        }
+
+        {
+            std::unique_lock lock(sig_mtx);
+            sig = ret == SIGUSR2 ? 0 : ret;
         }
+        sig_cv.notify_all();
 
         // if sig is SIGUSR2 then we know we're exiting because condition() was false
-        return sig == SIGUSR2 ? std::nullopt : std::make_optional(sig);
+        return ret == SIGUSR2 ? std::nullopt : std::make_optional(sig);
     };
 }
diff --git a/src/sshfs_mount/sshfs_server.cpp b/src/sshfs_mount/sshfs_server.cpp
index eb519a7895..ee49d7a3e5 100644
--- a/src/sshfs_mount/sshfs_server.cpp
+++ b/src/sshfs_mount/sshfs_server.cpp
@@ -117,7 +117,7 @@ int main(int argc, char* argv[])
         if (sig.has_value())
             cout << "Received signal " << *sig << ". Stopping" << endl;
         else
-            cout << "SFTP server thread stopped unexpectedly." << endl;
+            cerr << "SFTP server thread stopped unexpectedly." << endl;
 
         sshfs_mount.stop();
         exit(sig.has_value() ? EXIT_SUCCESS : EXIT_FAILURE);