Selecting data from a channel - go

Question

type Reader struct {
sync.RWMutex
logger *zerolog.Logger
wg *sync.WaitGroup
ticker *time.Ticker
messages chan *TransactionData
}
type TransactionData struct {
ID string
messages []*Message
}
func NewReader(logger zerolog.Logger) *Reader {
return &Reader{
wg: &sync.WaitGroup{},
logger: &l,
ticker: time.NewTicker(1 * time.Second),
messages: make(chan *TransactionData),
}
}
func (r *Reader) Write(ID string, messages []*Message) error {
r.wg.Add(1)
....
go func(ID string, messages []*domain.Message) {
defer r.wg.Done()
r.add(&TransactionData{
chatID: ID,
messages: messages,
})
}(ID, messages)
return nil
}
func (r *Reader) add(data *TransactionData) {
r.Lock()
defer r.Unlock()
r.messages <- data
}
func (r *Reader) get() {
r.Lock()
defer func() {
r.Unlock()
}()
for {
select {
case r.ticker.C:
// how to select all the data from the channel?
}
}
}
I'm exploring channels right now. And with the help of channels I'm trying to solve one problem.
Task: user reads chat history, selects all messages that user read, put these messages into channel, second channel selects data and creates transaction, through goroutine I add data into channel using Write method. I want to create a second goroutine which every second (using ticker.C) will select all the data from the channel and form a transaction. But I can't figure out how I can select all the data from the channel that I've managed to add there, example:
user-1: Write(&TransactionData{...}),
user-2: Write(&TransactionData{...}),
....
user-n: Write(&TransactionData{...})
How do I select absolutely all data and do I need to select all data or do I need to select one at a time?
Brief description of the solution:
Read from the channel in an infinite loop using goroutine
Put the subtracted tasks into the sync.Map thread-safe place
Run a second goroutine with time.Ticker.C and when it is triggered, select data for the transaction.
First question: How do I select all the data from the channel so that I collect one transaction and can update more data, provided that, I don't use any keys?(I attached an outline of the read method)
Second question: Should I get ALL the data from the channel or should I get only one TransactionData at a time and form one transaction?

Answer 1

There are several problems with your approach and implementation.
First: you don't need to lock a mutex to send to a channel.
Second: you don't need to lock a mutex to receive from a channel.
As for the implementation: since the channel is unbuffered, channel send will only work when there is a listening goroutine. If you receive from a channel when a ticker hits, then all the sends will happen after that ticker hits. Send operations will block until then.
So, you should get rid of that ticker, and read from the channel in a for-loop. When all the writes are completed, you should close the channel, which will terminate the for-loop, so you can write. Closing the channel is the idiomatic way of signaling to the receiver that all the data is sent.