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How are goroutines born?

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How are goroutines born?

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The go scheduler

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The pieces of the scheduler ● Status (Idle, running, syscall, gcstop) ● Current M ● Runnable goroutines ● Free gorotuines ● Other metadata P (the Processor) src/runtime/runtime2.go:609

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The pieces of the scheduler ● Current goroutine ● Current P ● Other metadata M (the Machine) src/runtime/runtime2.go:526

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The pieces of the scheduler ● Idle Ms ● Idle Ps ● Global runnable goroutines ● Global free goroutines ● Other metadata Sched (the Scheduler) src/runtime/runtime2.go:766

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The pieces of the scheduler ● Stack (2048 bytes) ● Program counter ● Status ● Current M ● Wait reason ● Other metadata. G (the Goroutine) src/runtime/runtime2.go:407

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All Ms All Ps All Goroutines The whole picture src/runtime/runtime2.go

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The birth of a goroutine

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The goroutine lifecycle Idle Dead Runnable Dead Runnable src/runtime/proc.go:4241 (newproc)

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All Ms All Ps All Goroutines The whole picture

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All Ms All Ps All Goroutines The whole picture

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All Ms All Ps All Goroutines The whole picture

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All Ms All Ps All Goroutines The whole picture

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All Ms All Ps All Goroutines The whole picture

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All Ms All Ps All Goroutines The whole picture

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All Ms All Ps All Goroutines The whole picture

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All Ms All Ps All Goroutines The whole picture

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All Ms All Ps All Goroutines The whole picture

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All Ms All Ps All Goroutines The whole picture

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All Ms All Ps All Goroutines The whole picture

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All Ms All Ps All Goroutines The whole picture

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All Ms All Ps All Goroutines The whole picture

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All Ms All Ps All Goroutines The whole picture

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The life of a goroutine

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The life of a goroutine Runnable Running Waiting Preempted Copystack Syscall

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Runnable to running ● Scheduler runs ● Find a goroutine to run ● Assigns it to the M ● Mark as Running ● Executes the code src/runtime/proc.go:3331 (schedule)

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Running to waiting ● Park itself ● Detach from M ● Run the scheduler src/runtime/proc.go:364 (gopark)

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waitReasonZero // "" waitReasonGCAssistMarking // "GC assist marking" waitReasonIOWait // "IO wait" waitReasonChanReceiveNilChan // "chan receive (nil chan)" waitReasonChanSendNilChan // "chan send (nil chan)" waitReasonDumpingHeap // "dumping heap" waitReasonGarbageCollection // "garbage collection" waitReasonGarbageCollectionScan // "garbage collection scan" waitReasonPanicWait // "panicwait" waitReasonSelect // "select" waitReasonSelectNoCases // "select (no cases)" waitReasonGCAssistWait // "GC assist wait" waitReasonGCSweepWait // "GC sweep wait" waitReasonGCScavengeWait // "GC scavenge wait" waitReasonChanReceive // "chan receive" waitReasonChanSend // "chan send" waitReasonFinalizerWait // "finalizer wait" waitReasonForceGCIdle // "force gc (idle)" waitReasonSemacquire // "semacquire" waitReasonSleep // "sleep" waitReasonSyncCondWait // "sync.Cond.Wait" waitReasonSyncMutexLock // "sync.Mutex.Lock" waitReasonSyncRWMutexRLock // "sync.RWMutex.RLock" waitReasonSyncRWMutexLock // "sync.RWMutex.Lock" waitReasonTraceReaderBlocked // "trace reader (blocked)" waitReasonWaitForGCCycle // "wait for GC cycle" waitReasonGCWorkerIdle // "GC worker (idle)" waitReasonGCWorkerActive // "GC worker (active)" waitReasonPreempted // "preempted" waitReasonDebugCall // "debug call" waitReasonGCMarkTermination // "GC mark termination" waitReasonStoppingTheWorld // "stopping the world" Running to waiting src/runtime/runtime2.go:14

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Running to waiting ● GC ● Mutex ● Semaphore ● Channel ● Sleep ● IO

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Running to syscall and to running or runnable ● On every syscall ● entersyscall is executed (moving to Sycall state) ● The syscall is executed ● exitsyscall is executed (moving back to Running/Runnable) src/runtime/proc.go:3825 (entersyscall) src/runtime/proc.go:3920 (exitsyscall)

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Running to copystack and back ● More stack needed ● Change Running to Copystack ● Grow the stack ● Change back to Running src/runtime/stack.go:964 (newstack)

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Waiting to runnable ● goready is called ● Is added to the queue ● Try to get a P src/runtime/proc.go:390 (goready)

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Waiting to runnable ● Reactivate a list of goroutines ● Mark all of them as runnable ● Wakes up all the Ps needed ● Add them to the queues src/runtime/proc.go:3255 (injectglist)

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Waiting to runnable ● Change to Waiting ● Donʼt need to wait ● Change to Runnable ● And then to Running rights away src/runtime/proc.go:3487 (park_m)

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Waiting to runnable ● Finding a goroutine ● Check in the netpoll ● Or wake up tasks for mark assist src/runtime/proc.go:2672 (findRunnable)

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Running to preempt, waiting and runnable ● Preempt flag is set ● Change to preempted ● Next GC change to waiting ● Do the GC scan ● Change to Runnable ● Add it back to the queue src/runtime/preempt.go:104 (suspendG) src/runtime/preempt.go:257 (resumeG)

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The goroutine lifecycle Runnable Running Waiting Preempted Copystack Syscall

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Examples

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channel The channel example data src/runtime/chan.go:160

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The channel example channel data src/runtime/chan.go:160

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The channel example channel data src/runtime/chan.go:457

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The channel example channel data ready data src/runtime/chan.go:615

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channel The channel example src/runtime/chan.go:615

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channel data channel The channel example data channel data channel data ready data channel

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create The waitgroup example add 3 Spawn Wait Group src/sync/waitgroup.go:43

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wait The waitgroup example Wait Group src/sync/waitgroup.go:91

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The waitgroup example Wait Group

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The waitgroup example Wait Group

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The waitgroup example Wait Group Ready Done src/sync/waitgroup.go:43

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The waitgroup example Wait Group

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Wait Group Wait Group Wait Group create The waitgroup example Add 3 Spawn wait Ready Done Wait Group

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The death of a goroutine

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The death of a goroutine ● A goroutine finish it work ● Change state to Dead ● Set most of the goroutine values to zero ● Disconnect the goroutine from the M ● Add the goroutine to the free list of the P ● Call the scheduler src/runtime/proc.go:3616 (goexit0)

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The whole life

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The whole picture All Ms All Ps All Goroutines

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The whole lifecycle Runnable Running Waiting Preempted Copystack Syscall Dead Idle

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Summary

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Illustrations ● CC-BY ● Created by Laura Pareja ● http://laurapareja.com

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A gift from Mattermost

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What is missing? ● The garbage collector ● The netpoll ● Cgo ● Mark assist ● Sysmon

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References ● The Go source code ● Illustrated Tales of Go Runtime Scheduler: https://www.youtube.com/watch?v=KxOwt6z0FvY ● Scheduling In Go: https://www.ardanlabs.com/blog/2018/08/scheduling-in-g o-part1.html

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Conclusions

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Let’s keep in touch jespinog jesus-espino jespino

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Let’s keep in touch https://forms.gle/rAFKZwVM4U26JPyn6