英文:
Go: using one channels to receive results from multiple goroutines
问题
我有一个包含数千条记录的CSV文件。
我在每个goroutine中处理每条记录，并希望将所有处理后的记录结果收集到一个切片中，以便将它们写入另一个文件。
代码的简化版本如下：
var wg sync.WaitGroup
func main() {
c := make(chan string, 1)
csvfile, err := os.Open("data.csv")
reader := csv.NewReader(bufio.NewReader(csvfile))
//...
for {
line, err := reader.Read()
// ...
wg.Add(1)
go processRecord(line, c)
}
//...
results := make([]string, 0)
for r := range c { // ERROR HERE: fatal error: all goroutines are asleep - deadlock!
results = append(results, r)
}
// write results to file
wg.Wait()
close(c)
}
func processRecord(data []string, c chan string) {
defer wg.Done()
// ...
c <- *result
}
在for循环中，我获取了所有的结果，但是在获取到最后一个结果后，循环继续执行，然后出现了这个错误：
fatal error: all goroutines are asleep - deadlock!
这段代码有什么问题？我在Stack Overflow上尝试了不同的问题和答案，但都没有成功解决。
英文:
I have a CSV file with thousands of records.
I process each record in a goroutine and I want to gather all the results of processed records in a slice to write them down in another file.
Simplified version of my code is:
var wg sync.WaitGroup
func main() {
c := make(chan string, 1)
csvfile, err := os.Open("data.csv")
reader := csv.NewReader(bufio.NewReader(csvfile))
//...
for {
line, err := reader.Read()
// ...
wg.Add(1)
go processRecord(line, c)
}
//...
results := make([]string, 0)
for r := range c { // ERROR HERE: fatal error: all goroutines are asleep - deadlock!
results = append(results , r)
}
// write results to file
wg.Wait()
close(c)
}
func processRecord(data []string, c chan string) {
defer wg.Done()
// ...
c <- *result
}
In for loop I get all the results but loop continues after getting last result and I get this error:
fatal error: all goroutines are asleep - deadlock!
What is wrong with this code? I tried different QAs on SO without any success.
答案1
得分: 3
for循环只有在通道关闭后才会终止。你是在for循环终止后关闭通道，因此导致了死锁。
你可以通过将for循环放入一个goroutine中来修复：
results := make([]string, 0)
done := make(chan struct{})
go func() {
for r := range c {
results = append(results, r)
}
close(done)
}()
wg.Wait()
close(c)
<-done
// 读取结果
英文:
The for-loop will only terminate once the channel is closed. You are closing the channel after for-loop terminates, hence the deadlock.
You can fix by putting the for-loop into a goroutine:
results := make([]string, 0)
done:=make(chan struct{})
go func() {
for r := range c {
results = append(results , r)
}
close(done)
}()
wg.Wait()
close(c)
<-done
// read results
答案2
得分: 0
你可以使用互斥锁（Mutex）来处理这个异常。以下是修复后的代码：
for r := range c {
mutex.Lock()
results = append(results, r)
mutex.Unlock()
}
通过使用互斥锁，可以确保在对results进行操作时只有一个goroutine可以访问它，从而避免了死锁的问题。
英文:
for r := range c { // ERROR HERE: fatal error: all goroutines are asleep - deadlock!
mutex.Lock()
results = append(results , r)
mutex.Unlock()
}
goroutines are asleep - deadlock! because its written at the same time. Use Mutex can be handle this exception
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