feat: add histograms; fix possible bugs

collector.v

@@ -7,51 +7,82 @@ struct CounterEntry {
 	index  int
 }
 
+struct HistogramEntry {
+	metric Metric
+pub mut:
+	data shared []f64
+}
+
 [heap]
 struct DefaultMetricsCollector {
 mut:
+	// The mutex for counters also applies to counter_indexes. Both data
+	// structuress are only ever updated together. Note that only registering a
+	// new metric actually changes these; all operations on already existing
+	// metrics use atomic operations on the elements of the counters array.
 	counters        shared []u64
-	counter_indexes shared map[string]CounterEntry
+	counter_indexes map[string]CounterEntry
+	histograms      shared map[string]HistogramEntry
 }
 
 pub fn new_default_metrics_collector() &DefaultMetricsCollector {
 	return &DefaultMetricsCollector{
 		counters: []u64{}
 		counter_indexes: map[string]CounterEntry{}
+		histograms: map[string]HistogramEntry{}
 	}
 }
 
 pub fn (mut c DefaultMetricsCollector) counter_register(value u64, metric Metric) {
-	new_index := lock c.counters {
+	lock c.counters {
 		c.counters << value
 
-		c.counters.len - 1
-	}
-
-	lock c.counter_indexes {
 		c.counter_indexes[metric.str()] = CounterEntry{
 			metric: metric
-			index: new_index
+			index: c.counters.len - 1
 		}
 	}
 }
 
 pub fn (mut c DefaultMetricsCollector) counter_increment(metric Metric) {
-	entry := rlock c.counter_indexes {
-		c.counter_indexes[metric.str()]
-	}
-
 	rlock c.counters {
+		entry := c.counter_indexes[metric.str()]
+
 		stdatomic.add_u64(&c.counters[entry.index], 1)
 	}
 }
 
 pub fn (mut c DefaultMetricsCollector) counter_decrement(metric Metric) {
-	entry := rlock c.counter_indexes {
-		c.counter_indexes[metric.str()]
-	}
-
 	rlock c.counters {
+		entry := c.counter_indexes[metric.str()]
+
 		stdatomic.sub_u64(&c.counters[entry.index], 1)
 	}
 }
+
+pub fn (mut c DefaultMetricsCollector) counter_get(metric Metric) ?u64 {
+	return rlock c.counters {
+		entry := c.counter_indexes[metric.str()] or { return none }
+
+		stdatomic.load_u64(&c.counters[entry.index])
+	}
+}
+
+pub fn (mut c DefaultMetricsCollector) histogram_register(metric Metric) {
+	lock c.histograms {
+		c.histograms[metric.str()] = HistogramEntry{
+			metric: metric
+			data: []f64{}
+		}
+	}
+}
+
+pub fn (mut c DefaultMetricsCollector) histogram_add(value f64, metric Metric) {
+	entry := rlock c.histograms {
+		c.histograms[metric.str()]
+	}
+
+	lock entry.data {
+		entry.data << value
+	}
+}