Synchronizing function return when using goroutines, and channels
Here is part of my implementation of reading a Kinesis stream. I am not confident that this is the best way to implement synchronizing returns from goroutine.
Assuming there are N shards in the stream, the code spawns goroutines for each shard in the stream for processing. Goroutine-N works indefinitely until the underlying context is canceled or until an error is encountered during processing.
The code below is supposed to wait for all N routines to terminate successfully (i.e without any of them writing to errc) or wait for at least one routine to write to errc (return an error).
If all routines terminate without writing to errc, the WaitGroup sync lock is released, closing the errc and done channels. Which would, in turn, resume the current thread. However, if one of the routines terminate writing to errc, we force all routines to terminate by calling the underlying context's cancel function and wait for done channel to close.
func (c *Consumer) scanShards(col Collector, streamName string, ids string) error {
checkpoints, err := col.GetSequenceNumberForShards(streamName, ids)
if err != nil {
return fmt.Errorf("error retrieving stored checkpoints for shards: %v", err)
}
errc := make(chan error, 1)
done := make(chan error, 1)
wg := sync.WaitGroup{}
wg.Add(len(ids))
for _, id := range ids {
seqNum := checkpoints[id]
ctx, cancel := context.WithCancel(context.Background())
c.cancelFuncs = append(c.cancelFuncs, cancel)
go func(ctx context.Context, shardID, startSeqNum string) {
defer wg.Done()
if err := c.scanShard(ctx, shardID, startSeqNum); err != nil {
errc <- fmt.Errorf("error in shard %q: %v", shardID, err)
}
}(ctx, id, seqNum)
}
go func() {
wg.Wait()
close(errc)
close(done)
}()
err = <-errc
if err != nil {
// Cancel all scans, to release the worker goroutines from
// the pool.
for _, cancel := range c.cancelFuncs {
cancel()
}
}
<-done // Wait for all goroutines to exit.
return err
}
go
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Here is part of my implementation of reading a Kinesis stream. I am not confident that this is the best way to implement synchronizing returns from goroutine.
Assuming there are N shards in the stream, the code spawns goroutines for each shard in the stream for processing. Goroutine-N works indefinitely until the underlying context is canceled or until an error is encountered during processing.
The code below is supposed to wait for all N routines to terminate successfully (i.e without any of them writing to errc) or wait for at least one routine to write to errc (return an error).
If all routines terminate without writing to errc, the WaitGroup sync lock is released, closing the errc and done channels. Which would, in turn, resume the current thread. However, if one of the routines terminate writing to errc, we force all routines to terminate by calling the underlying context's cancel function and wait for done channel to close.
func (c *Consumer) scanShards(col Collector, streamName string, ids string) error {
checkpoints, err := col.GetSequenceNumberForShards(streamName, ids)
if err != nil {
return fmt.Errorf("error retrieving stored checkpoints for shards: %v", err)
}
errc := make(chan error, 1)
done := make(chan error, 1)
wg := sync.WaitGroup{}
wg.Add(len(ids))
for _, id := range ids {
seqNum := checkpoints[id]
ctx, cancel := context.WithCancel(context.Background())
c.cancelFuncs = append(c.cancelFuncs, cancel)
go func(ctx context.Context, shardID, startSeqNum string) {
defer wg.Done()
if err := c.scanShard(ctx, shardID, startSeqNum); err != nil {
errc <- fmt.Errorf("error in shard %q: %v", shardID, err)
}
}(ctx, id, seqNum)
}
go func() {
wg.Wait()
close(errc)
close(done)
}()
err = <-errc
if err != nil {
// Cancel all scans, to release the worker goroutines from
// the pool.
for _, cancel := range c.cancelFuncs {
cancel()
}
}
<-done // Wait for all goroutines to exit.
return err
}
go
asked 33 mins ago
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Here is part of my implementation of reading a Kinesis stream. I am not confident that this is the best way to implement synchronizing returns from goroutine.
Assuming there are N shards in the stream, the code spawns goroutines for each shard in the stream for processing. Goroutine-N works indefinitely until the underlying context is canceled or until an error is encountered during processing.
The code below is supposed to wait for all N routines to terminate successfully (i.e without any of them writing to errc) or wait for at least one routine to write to errc (return an error).
If all routines terminate without writing to errc, the WaitGroup sync lock is released, closing the errc and done channels. Which would, in turn, resume the current thread. However, if one of the routines terminate writing to errc, we force all routines to terminate by calling the underlying context's cancel function and wait for done channel to close.
func (c *Consumer) scanShards(col Collector, streamName string, ids string) error {
checkpoints, err := col.GetSequenceNumberForShards(streamName, ids)
if err != nil {
return fmt.Errorf("error retrieving stored checkpoints for shards: %v", err)
}
errc := make(chan error, 1)
done := make(chan error, 1)
wg := sync.WaitGroup{}
wg.Add(len(ids))
for _, id := range ids {
seqNum := checkpoints[id]
ctx, cancel := context.WithCancel(context.Background())
c.cancelFuncs = append(c.cancelFuncs, cancel)
go func(ctx context.Context, shardID, startSeqNum string) {
defer wg.Done()
if err := c.scanShard(ctx, shardID, startSeqNum); err != nil {
errc <- fmt.Errorf("error in shard %q: %v", shardID, err)
}
}(ctx, id, seqNum)
}
go func() {
wg.Wait()
close(errc)
close(done)
}()
err = <-errc
if err != nil {
// Cancel all scans, to release the worker goroutines from
// the pool.
for _, cancel := range c.cancelFuncs {
cancel()
}
}
<-done // Wait for all goroutines to exit.
return err
}
go
asked 33 mins ago
States
101
New contributor
States is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Here is part of my implementation of reading a Kinesis stream. I am not confident that this is the best way to implement synchronizing returns from goroutine.
Assuming there are N shards in the stream, the code spawns goroutines for each shard in the stream for processing. Goroutine-N works indefinitely until the underlying context is canceled or until an error is encountered during processing.
The code below is supposed to wait for all N routines to terminate successfully (i.e without any of them writing to errc) or wait for at least one routine to write to errc (return an error).
If all routines terminate without writing to errc, the WaitGroup sync lock is released, closing the errc and done channels. Which would, in turn, resume the current thread. However, if one of the routines terminate writing to errc, we force all routines to terminate by calling the underlying context's cancel function and wait for done channel to close.
func (c *Consumer) scanShards(col Collector, streamName string, ids string) error {
checkpoints, err := col.GetSequenceNumberForShards(streamName, ids)
if err != nil {
return fmt.Errorf("error retrieving stored checkpoints for shards: %v", err)
}
errc := make(chan error, 1)
done := make(chan error, 1)
wg := sync.WaitGroup{}
wg.Add(len(ids))
for _, id := range ids {
seqNum := checkpoints[id]
ctx, cancel := context.WithCancel(context.Background())
c.cancelFuncs = append(c.cancelFuncs, cancel)
go func(ctx context.Context, shardID, startSeqNum string) {
defer wg.Done()
if err := c.scanShard(ctx, shardID, startSeqNum); err != nil {
errc <- fmt.Errorf("error in shard %q: %v", shardID, err)
}
}(ctx, id, seqNum)
}
go func() {
wg.Wait()
close(errc)
close(done)
}()
err = <-errc
if err != nil {
// Cancel all scans, to release the worker goroutines from
// the pool.
for _, cancel := range c.cancelFuncs {
cancel()
}
}
<-done // Wait for all goroutines to exit.
return err
}
go
go
asked 33 mins ago
States
101
New contributor
States is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 33 mins ago
States
101
New contributor
States is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 33 mins ago
States
101
New contributor
States is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 33 mins ago
States
101
asked 33 mins ago
States
101
101
New contributor
States is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
States is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
States is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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