From 1623b6a71fb59d7fc09e87f35286d7ccfa9034e9 Mon Sep 17 00:00:00 2001
From: Maxim Prokhorov <prokhorov.max@outlook.com>
Date: Thu, 19 Jan 2023 18:38:07 +0300
Subject: [PATCH 1/2] Ticker callback should be allowed to be destroyed

Mainly, we protect std::function and variant itself from undefined
behaviour when the underlying object is destroyed and then re-created
with something else inside of it.

For example, every captured object would be destroyed.
```cpp
Ticker ticker;
void oops(Job job) {
    ticker.once(1.0f,
        [job = std::move(job)]() {
            ticker.once(job.next(), do_something_else);
            job.work(); // ~Job() just happened!
        });
}
```

Another important case is repeating through once()
```cpp
Ticker ticker;
void repeat() {
    ticker.once(1.0f, repeat);
    puts("tick");
}

void setup() {
    repeat();
}
```

Temporarily moving callback object into the function and returning
earlier should solve both cases.
---
 libraries/Ticker/src/Ticker.cpp | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/libraries/Ticker/src/Ticker.cpp b/libraries/Ticker/src/Ticker.cpp
index baac355ca5..9eca8512c8 100644
--- a/libraries/Ticker/src/Ticker.cpp
+++ b/libraries/Ticker/src/Ticker.cpp
@@ -115,6 +115,10 @@ void Ticker::_static_callback()
         }
     }
 
+    // it is technically allowed to call either schedule or detach
+    // *during* callback execution. allow both to happen
+    auto tmp = std::move(_callback);
+
     std::visit([](auto&& callback) {
         using T = std::decay_t<decltype(callback)>;
         if constexpr (std::is_same_v<T, callback_ptr_t>) {
@@ -122,7 +126,16 @@ void Ticker::_static_callback()
         } else if constexpr (std::is_same_v<T, callback_function_t>) {
             callback();
         }
-    }, _callback);
+    }, tmp);
+
+    // ...and move ourselves back only when object is in a valid state
+    // * ticker was not detached, zeroing timer pointer
+    // * nothing else replaced callback variant
+    if ((_timer == nullptr) || !std::holds_alternative<std::monostate>(_callback)) {
+        return;
+    }
+
+    _callback = std::move(tmp);
 
     if (_repeat) {
         if (_tick) {

From 1261b28c8a2acc213f1fe536945a66db5fd171d6 Mon Sep 17 00:00:00 2001
From: Maxim Prokhorov <prokhorov.max@outlook.com>
Date: Fri, 20 Jan 2023 20:33:07 +0300
Subject: [PATCH 2/2] words

---
 libraries/Ticker/src/Ticker.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/libraries/Ticker/src/Ticker.cpp b/libraries/Ticker/src/Ticker.cpp
index 9eca8512c8..8c45ffed8b 100644
--- a/libraries/Ticker/src/Ticker.cpp
+++ b/libraries/Ticker/src/Ticker.cpp
@@ -117,7 +117,8 @@ void Ticker::_static_callback()
 
     // it is technically allowed to call either schedule or detach
     // *during* callback execution. allow both to happen
-    auto tmp = std::move(_callback);
+    decltype(_callback) tmp;
+    std::swap(tmp, _callback);
 
     std::visit([](auto&& callback) {
         using T = std::decay_t<decltype(callback)>;
@@ -135,7 +136,7 @@ void Ticker::_static_callback()
         return;
     }
 
-    _callback = std::move(tmp);
+    std::swap(tmp, _callback);
 
     if (_repeat) {
         if (_tick) {