record building partitions to enable more accurate want state setting

databuild/build_state.rs

@@ -1151,10 +1151,10 @@ impl BuildState {
     }
 
     /**
-    Wants are schedulable when their partition is live and not tainted
+    Wants are schedulable when their upstreams are ready and target partitions are not already building
     */
     pub fn want_schedulability(&self, want: &WantDetail) -> WantSchedulability {
-        // Use type-safe partition checks from partitions
+        // Check upstream partition statuses (dependencies)
         let mut live: Vec<LivePartitionRef> = Vec::new();
         let mut tainted: Vec<TaintedPartitionRef> = Vec::new();
         let mut missing: Vec<MissingPartitionRef> = Vec::new();
@@ -1178,12 +1178,24 @@ impl BuildState {
             }
         }
 
+        // Check target partition statuses (what this want is trying to build)
+        // If any target partition is already Building, this want should wait
+        let mut building: Vec<BuildingPartitionRef> = Vec::new();
+        for target_ref in &want.partitions {
+            if let Some(partition) = self.partitions.get(&target_ref.r#ref) {
+                if let Partition::Building(p) = partition {
+                    building.push(p.get_ref());
+                }
+            }
+        }
+
         WantSchedulability {
             want: want.clone(),
             status: WantUpstreamStatus {
                 live,
                 tainted,
                 missing,
+                building,
             },
         }
     }
@@ -1206,6 +1218,8 @@ pub struct WantUpstreamStatus {
     pub live: Vec<LivePartitionRef>,
     pub tainted: Vec<TaintedPartitionRef>,
     pub missing: Vec<MissingPartitionRef>,
+    /// Target partitions that are currently being built by another job
+    pub building: Vec<BuildingPartitionRef>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize, Default)]
@@ -1231,7 +1245,13 @@ impl WantsSchedulability {
 
 impl WantSchedulability {
     pub fn is_schedulable(&self) -> bool {
-        self.status.missing.is_empty() && self.status.tainted.is_empty()
+        // Want is schedulable if:
+        // - No missing upstream dependencies
+        // - No tainted upstream dependencies
+        // - No target partitions currently being built by another job
+        self.status.missing.is_empty()
+            && self.status.tainted.is_empty()
+            && self.status.building.is_empty()
     }
 }