Use SeqCst ordering as we aren't sure how collectd is calling us

CHANGELOG.md

@@ -133,7 +133,7 @@ impl Plugin for MyErrorPlugin {
     }
 
     fn read_values(&self) -> Result<(), Box<error::Error>> {
-        if self.state.fetch_xor(true, Ordering::Relaxed) {
+        if self.state.fetch_xor(true, Ordering::SeqCst) {
             panic!("Oh dear what is wrong!?")
         } else {
             Err(failure::err_msg("bailing"))?

examples/myerror.rs

@@ -41,7 +41,7 @@ impl Plugin for MyErrorPlugin {
     }
 
     fn read_values(&self) -> Result<(), Box<dyn error::Error>> {
-        if self.state.fetch_xor(true, Ordering::Relaxed) {
+        if self.state.fetch_xor(true, Ordering::SeqCst) {
             panic!("Oh dear what is wrong!?")
         } else {
             Err(failure::err_msg("bailing").into())

src/internal.rs

@@ -214,7 +214,7 @@ fn register_all_plugins<T: PluginManager>(config: Option<&[ConfigItem<'_>]>) ->
 }
 
 pub fn plugin_init<T: PluginManager>(config_seen: &AtomicBool) -> c_int {
-    let mut result = if !config_seen.swap(true, Ordering::Relaxed) {
+    let mut result = if !config_seen.swap(true, Ordering::SeqCst) {
         register_all_plugins::<T>(None)
     } else {
         0
@@ -262,7 +262,7 @@ pub unsafe fn plugin_complex_config<T: PluginManager>(
 ) -> c_int {
     // If we've already seen the config, let's error out as one shouldn't use multiple
     // sections of configuration (group them under nodes like write_graphite)
-    if config_seen.swap(true, Ordering::Relaxed) {
+    if config_seen.swap(true, Ordering::SeqCst) {
         log_err("config", &FfiError::MultipleConfig);
         return -1;
     }