Hi Gophers!
I am trying to work with web assembly and got stuck with a deadlock problem,
The main function has nothing more than simple steps, but if someone wants
to check, it is at https://go.dev/play/p/y_0aiIzFA0j .
It imports an internal package so it is not compilable outside my computer,
it is at the Go Playground just to show the source if someone wants to see
it.
So, it sets a javascript callable function exported as img2data. The
purpose of the function is to receive an HTML string and check each image
reference (IMG tags and alse elements with "background-image: url(...)"
style), download the image, generate a data URL, and finally replacing the
reference in the HTML with the data URL.
But when it starts the process it deadlocks at the very first image it
finds. The panic message is as follows:
2022/06/16 17:19:01 {main}[Img2data-wasm.go]<main.func1>(26): Calling
Img2data
wasm_exec.js:51 2022/06/16 17:19:01 {Img2data}[Img2data.go]<Img2data>(21):
START
8wasm_exec.js:51 2022/06/16 17:19:02
{Img2data}[Img2data.go]<Img2data.func1>(30): NOSCRIPT
wasm_exec.js:51 2022/06/16 17:19:02
{Img2data}[Img2data.go]<Img2data.func2>(41): IMG
wasm_exec.js:51 2022/06/16 17:19:02
{Img2data}[Img2data.go]<Img2data.func2>(44): img: src=https://<censored
image url>.png
wasm_exec.js:51 2022/06/16 17:19:02
{Img2data}[Img2data.go]<Img2data.func2>(46): img: src=https://<censored
image url>.png
wasm_exec.js:51 fatal error: all goroutines are asleep - deadlock!
wasm_exec.js:51
wasm_exec.js:51 goroutine 1 [chan receive]:
wasm_exec.js:51 main.main()
wasm_exec.js:51 /home/vuco/repos/mpf/Img2data/cmd/Img2data-wasm.go:35 +0xa
wasm_exec.js:51
wasm_exec.js:51 goroutine 6 [select]:
wasm_exec.js:51 net/http.(*Transport).RoundTrip(0x36c640, 0x1a0a200,
0x36c640, 0x0, 0x0)
wasm_exec.js:51 /home/vuco/repos/go/src/net/http/roundtrip_js.go:169 +0x4f
wasm_exec.js:51 net/http.send(0x1a0a200, 0xe14d8, 0x36c640, 0x0, 0x0, 0x0,
0x0, 0x40c0b8, 0x718ed0, 0x1)
wasm_exec.js:51 /home/vuco/repos/go/src/net/http/client.go:251 +0x5b
wasm_exec.js:51 net/http.(*Client).send(0x379940, 0x1a0a200, 0x0, 0x0, 0x0,
0x40c0b8, 0x0, 0x1, 0x1a0a200)
wasm_exec.js:51 /home/vuco/repos/go/src/net/http/client.go:175 +0x13
wasm_exec.js:51 net/http.(*Client).do(0x379940, 0x1a0a200, 0x0, 0x0, 0x0)
wasm_exec.js:51 /home/vuco/repos/go/src/net/http/client.go:717 +0x36
wasm_exec.js:51 net/http.(*Client).Do(...)
wasm_exec.js:51 /home/vuco/repos/go/src/net/http/client.go:585
wasm_exec.js:51 net/http.(*Client).Get(0x379940, 0x4c4320, 0x4e, 0xb,
0x1a05d50, 0x1)
wasm_exec.js:51 /home/vuco/repos/go/src/net/http/client.go:474 +0xe
wasm_exec.js:51 net/http.Get(...)
wasm_exec.js:51 /home/vuco/repos/go/src/net/http/client.go:446
wasm_exec.js:51 mpf/Img2data.Img2data.func2(0x0, 0x718de0)
wasm_exec.js:51 /home/vuco/repos/mpf/Img2data/Img2data.go:48 +0x19
wasm_exec.js:51 github.com/PuerkitoBio/goquery.(*Selection).Each(0x718db0,
0xa8378, 0x3)
wasm_exec.js:51 /home/vuco/repos/gopkg/pkg/mod/
github.com/!puerkito!bio/goquery@v1.8.0/iteration.go:10 +0x16
wasm_exec.js:51 mpf/Img2data.Img2data(0x2000000, 0x9ef7fd, 0x2000000,
0x9ef7fd, 0x0, 0x0)
wasm_exec.js:51 /home/vuco/repos/mpf/Img2data/Img2data.go:34 +0x14
wasm_exec.js:51 main.main.func1(0x0, 0x0, 0x40ec60, 0x1, 0x1, 0x4102b8,
0x3a0108)
wasm_exec.js:51 /home/vuco/repos/mpf/Img2data/cmd/Img2data-wasm.go:28 +0x10
wasm_exec.js:51 syscall/js.handleEvent()
wasm_exec.js:51 /home/vuco/repos/go/src/syscall/js/func.go:96 +0x24
I shared the point of the code where it panics at
https://go.dev/play/p/3chb2eQo8sD . Again, it is not runnable, it's just
there to check the code. It panics at line 15.
The point is: there is only 2 goroutines (done by me, I don't know about
other go routines started by the libraries)
1) the main function running, but, as learnt from golang wasm tutorial, it
is doing nothing, just waiting forever for a channel read that will never
read anything,
2) the img2data function that tries to download the images ang, when I call
the http.Get it goes to sleep waiting for the server to answer the request
and at this very moment all my goroutines are sleeping ang the runtime
detects this condition and panics!
I also tried to make the main function do something while it waits forever
by using a "for{}", it did not panicked, but I got stuck anyway and I
suspect that it is because in the web assembly runtime only one goroutine
can execute until it sleeps and leave place for other goroutines and doing
a "for{}" makes the main function run forever but it never allows the
img2data function to be run.
So, someone could help me on how to solve this problem?
Thank you in advance!
Best regards,
--
Luis Otavio de Colla Furquim
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