Concurrency is about executing a multiple code snippets in a context switching manner. Go, by default, executes code sequentially. Concurrency can be handy when there are multiple conde snippets that are independent (or sort of) from each other, calls that are blocking. Executing them concurrently can save up time. Usually threads or processes are used to achieve this behaviour. In Go, goroutines are used to achieve this.
Go routines are green threads that internally take care of resource management with the kernel of the system.
Placing go keyword before the function call, starts the function execution is a new go routine.
It is important to understand that concurrency is different from parallelism. At a time one code line is executed.
There can be a delay in getting the output of that line (blocking call). At that point, some other line is also triggered.
Go Scheduler by default run on only one CPU. It monitors the code running each routine.
Multiple cores can be used by explicitly mentioning it. In this case, parallel execution of code takes place.
This triggers a huge debate about concurrency and parallelism.
for k, v := range my_map {
go call_my_function(key, value)
}When a program is executed, the first go routine is triggered. This is called the main routine.
The routines spawned by user are called child routines.
Main routines controls the time when the program exits. It does NOT take into account the half executed child routines.
This means that, once the code inside main function is complete, the program exits.
Note that values should not passed by reference between go rountines, especially when both are working on the same
variable.
Channels are used to establish communication between routines, main and child, both. It can be used to share messages of only one datatype. This data type is declared while declaring the channel. No other data type values can be placed inside the channel. Below is the code for declaring a channel for string message.
c := make(chan string)At a time, only one string can be placed into the channel.
To put a message into a channel, the syntax is my_channel <- "Hello
To receive a message from channel , the syntax is my_msg := <- my_channel
Waiting to receive message from a channel is blocking call.
func dummy(s string, c chan string) {
c<-"Hola"
}