This is going to create 5000 OS threads. The loop runs really quickly, and since CGO cannot use Go routines, you quickly allocate 5000 OS threads.
See https://github.com/golang/go/issues/14592 > On Mar 4, 2025, at 1:26 PM, David Bell <davidbellou...@gmail.com> wrote: > > Hi everyone, > > I'm relatively new to Go and even newer to CGO, so I’d really appreciate any > guidance on an issue I’ve been facing. > > Problem Overview > > I noticed that when using CGO, my application's memory usage keeps > increasing, and threads do not seem to be properly cleaned up. > The Go runtime (pprof) does not indicate any leaks, but when I monitor the > process using Activity Monitor, I see a growing number of threads and > increasing memory consumption. > > Observations > Memory usage keeps increasing over time when using CGO, even after forcing > garbage collection. > Threads spawned for CGO calls appear to not be released, causing a large > number of lingering threads. > The issue is not present when using pure Go time.Sleep() instead of the CGO > function. > Reproducible Example > > I created a minimal program that reproduces the issue. The following > CGO-based code keeps allocating memory and does not free threads properly: > > package main > > import ( > "fmt" > "runtime" > "runtime/debug" > "sync" > "time" > ) > > /* > #include <unistd.h> > void cgoSleep() { > sleep(1); > } > */ > import "C" > > func main() { > start := time.Now() > > var wg sync.WaitGroup > for i := 0; i < 5000; i++ { > wg.Add(1) > go func() { > defer wg.Done() > C.cgoSleep() > }() > } > wg.Wait() > > end := time.Now() > > // Force GC and free OS memory > runtime.GC() > debug.FreeOSMemory() > time.Sleep(10 * time.Second) > > var m runtime.MemStats > runtime.ReadMemStats(&m) > > fmt.Printf("Alloc = %v MiB", m.Alloc/1024/1024) > fmt.Printf("\tTotalAlloc = %v MiB", m.TotalAlloc/1024/1024) > fmt.Printf("\tSys = %v MiB", m.Sys/1024/1024) > fmt.Printf("\tNumGC = %v\n", m.NumGC) > fmt.Printf("Total time: %v\n", end.Sub(start)) > > select {} > } > > Expected Behavior > The memory usage should not continue rising indefinitely. > Threads should be properly cleaned up when they finish executing. > The behavior should be similar to the following pure Go equivalent, which > does not exhibit the issue: > > > Actual Results With CGO (cgoSleep()): > Memory Usage: 296 MB > Threads: 5,003 > System Memory (Sys from runtime.MemStats): 205 MB > > > With Pure Go (time.Sleep()): > Memory Usage: 14 MB > Threads: 14 > System Memory (Sys from runtime.MemStats): 24 MB > Additional Attempt > I tried forcing thread cleanup using runtime.LockOSThread() and > runtime.Goexit(), but while the number of threads decreases, memory is still > never fully released: > > go func() { runtime.LockOSThread() defer wg.Done() C.cgoSleep() > runtime.Goexit() }() Questions > Why is memory increasing indefinitely with CGO? > Why are threads not getting properly cleaned up after CGO calls? > Is there a way to force the Go runtime to reclaim memory allocated for CGO > threads? > Is there a better approach to handling CGO calls that spawn short-lived > threads? > Would using runtime.UnlockOSThread() help in this case, or is this purely a > CGO threading issue? > Is there a way to track down where the memory is being held? Since pprof does > not show high memory usage, what other tools can I use? > Go Version > go1.23.5 darwin/arm64 > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com > <mailto:golang-nuts+unsubscr...@googlegroups.com>. > To view this discussion visit > https://groups.google.com/d/msgid/golang-nuts/5e8c1622-e6f0-47a8-a869-e78797800fb5n%40googlegroups.com > > <https://groups.google.com/d/msgid/golang-nuts/5e8c1622-e6f0-47a8-a869-e78797800fb5n%40googlegroups.com?utm_medium=email&utm_source=footer>. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/golang-nuts/0628BDD7-D9AE-4F22-B5AA-8F0ACB873B98%40ix.netcom.com.
