Fix race conditions

- Wait for completions of goroutines when cancelling a search
- Remove shared access to rank field of Item

src/matcher.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"runtime"
 	"sort"
+	"sync"
 	"time"
 )
 
@@ -134,10 +135,13 @@ func (m *Matcher) scan(request MatchRequest, limit int) (*Merger, bool) {
 	slices := m.sliceChunks(request.chunks)
 	numSlices := len(slices)
 	resultChan := make(chan partialResult, numSlices)
-	countChan := make(chan int, numSlices)
+	countChan := make(chan int, numChunks)
+	waitGroup := sync.WaitGroup{}
 
 	for idx, chunks := range slices {
+		waitGroup.Add(1)
 		go func(idx int, chunks []*Chunk) {
+			defer func() { waitGroup.Done() }()
 			sliceMatches := []*Item{}
 			for _, chunk := range chunks {
 				var matches []*Item
@@ -159,6 +163,12 @@ func (m *Matcher) scan(request MatchRequest, limit int) (*Merger, bool) {
 		}(idx, chunks)
 	}
 
+	wait := func() bool {
+		cancelled.Set(true)
+		waitGroup.Wait()
+		return true
+	}
+
 	count := 0
 	matchCount := 0
 	for matchesInChunk := range countChan {
@@ -166,7 +176,7 @@ func (m *Matcher) scan(request MatchRequest, limit int) (*Merger, bool) {
 		matchCount += matchesInChunk
 
 		if limit > 0 && matchCount > limit {
-			return nil, true // For --select-1 and --exit-0
+			return nil, wait() // For --select-1 and --exit-0
 		}
 
 		if count == numChunks {
@@ -174,8 +184,7 @@ func (m *Matcher) scan(request MatchRequest, limit int) (*Merger, bool) {
 		}
 
 		if !empty && m.reqBox.Peak(REQ_RESET) {
-			cancelled.Set(true)
-			return nil, true
+			return nil, wait()
 		}
 
 		if time.Now().Sub(startedAt) > PROGRESS_MIN_DURATION {