Crash under stress test

[1a1a11a]

Hi there,
I tried to use it with fasthttp, but it seems it crashes immediately after I use multiple clients, the code involved are

    

    cachedContent, _ = cache.Get(req)
    if len(cachedContent) != 0{
        ctx.Response.Header.Set("CacheHit", "frontendRAM")
        ctx.SetBody(cachedContent)
    }else{

        cachedContent = []byte("objContents")

        // save to memory
        _ = cache.Set(req, cachedContent, 0)
        ctx.Response.Header.Set("CacheHit", "chunkServerDecode")
    }

Hers is the stack trace

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x458ee6]

goroutine 40 [running]:
github.com/coocood/freecache.(*RingBuf).Write(0xc0bed84240, 0x0, 0xb, 0x0, 0xc, 0x0, 0x0)
    /home/ubuntu/src/github.com/coocood/freecache/ringbuf.go:89 +0x101
github.com/coocood/freecache.(*segment).set(0xc0bed84240, 0xc10bd3cdc8, 0xc, 0x18, 0x0, 0xb, 0x0, 0xe8a4600e8662d28, 0x0, 0xc10e2d5160, ...)
    /home/ubuntu/src/github.com/coocood/freecache/segment.go:144 +0x56b
github.com/coocood/freecache.(*Cache).Set(0xc0bed78000, 0xc10bd3cdc8, 0xc, 0x18, 0x0, 0xb, 0x0, 0x0, 0xc000010260, 0x0)
    /home/ubuntu/src/github.com/coocood/freecache/cache.go:53 +0x112
main.akamaiHandler(0xc10bd1f400)
    /home/ubuntu/src/frontend/main.go:189 +0x595
main.requestHandler(0xc10bd1f400)
    /home/ubuntu/src/frontend/main.go:87 +0x124
github.com/valyala/fasthttp.(*Server).serveConn(0xc10bcb6000, 0x725bc0, 0xc10bd0c020, 0x0, 0x0)
    /home/ubuntu/src/github.com/valyala/fasthttp/server.go:1932 +0x6f7
github.com/valyala/fasthttp.(*Server).serveConn-fm(0x725bc0, 0xc10bd0c020, 0x1, 0x0)
    /home/ubuntu/src/github.com/valyala/fasthttp/server.go:1538 +0x3e
github.com/valyala/fasthttp.(*workerPool).workerFunc(0xc10bcc2000, 0xc10bce0220)
    /home/ubuntu/src/github.com/valyala/fasthttp/workerpool.go:212 +0xc3
github.com/valyala/fasthttp.(*workerPool).getCh.func1(0xc10bcc2000, 0xc10bce0220, 0x665a00, 0xc10bce0220)
    /home/ubuntu/src/github.com/valyala/fasthttp/workerpool.go:184 +0x35
created by github.com/valyala/fasthttp.(*workerPool).getCh
    /home/ubuntu/src/github.com/valyala/fasthttp/workerpool.go:183 +0x119
exit status 2

[coocood]

How is the cache created?

[1a1a11a]

Hi @coocood, here is what I have done for cache initialization.

Cache = freecache.NewCache(ramCacheSize)
debug.SetGCPercent(20)

[coocood]

Do you have any cache instance created by new(freecache.Cache)?
From the stack, it seems like the RingBuf is nil, it only happens when cache is created by new(freecache.Cache.

[1a1a11a]

No I don't. But in order to be accessed by handler, I have the cache as global variable, var Cache *freecache.Cache, then in the main function, I have Cache = freecache.NewCache(ramCacheSize).

[1a1a11a]

I double checked that it only happens if there are multiple clients writing to it, if I wrap the set with lock, then it won't crash.

[1a1a11a]

I can send a full test if that would be helpful.

[1a1a11a]

OK, I am wrong, it does happen if I let it run longer, so it is not write data race problem.

[coocood]

@1a1a11a
Please provide the full test that can reproduce this issue.
Thank you.

[coocood]

There is another possibility that the value passed to Set is nil.
You can try to add this code to verify if this is the case.

hdr := (*reflect.SliceHeader)(unsafe.Pointer(&cachedContent))
fmt.Println(hdr.Data, hdr.Len, hdr.Cap)

If the hdr.Data is 0, then this is the cause of the crash.

[1a1a11a]

This is useful, the data passed to set was nil, now it works like a charm. Thank you!