README: edit goroutine limitation

Signed-off-by: mathetake <[email protected]>

Author: mathetake

README.md

@@ -92,20 +92,23 @@ make test.e2e # run e2e tests
         2. TinyGo does not implement all of reflect package([examples](https://github.com/tinygo-org/tinygo/blob/v0.14.1/src/reflect/value.go#L299-L305)).
         3. [proxy-wasm-cpp-host](https://github.com/proxy-wasm/proxy-wasm-cpp-host) has not supported some of WASI APIs yet 
         (see the [supported functions](https://github.com/proxy-wasm/proxy-wasm-cpp-host/blob/master/include/proxy-wasm/exports.h#L134-L147)).
-         For example, `clock_time_get` is not implemented, and therefore we cannot use `time.Now`.
+         For example, `clock_time_get` is not implemented, and therefore we cannot use `time.Now` function.
     - These issues will be mitigated as TinyGo and proxy-wasm-cpp-host evolve.
-- There's performance overhead in using Go/TinyGo due to GC
-    - runtime.GC() is called whenever the heap runs out (see [1](https://tinygo.org/lang-support/#garbage-collection),
+- There's performance overhead of using Go/TinyGo due to GC
+    - `runtime.GC` is called whenever the heap runs out (see [1](https://tinygo.org/lang-support/#garbage-collection),
     [2](https://github.com/tinygo-org/tinygo/blob/v0.14.1/src/runtime/gc_conservative.go#L218-L239)).
     - TinyGo allows us to disable GC, but we cannot do that since we need to use maps (implicitly causes allocation)
-     for saving the plugin's [state](https://github.com/tetratelabs/proxy-wasm-go-sdk/blob/master/proxywasm/vmstate.go#L17-L22).
+     for saving the plugin's [state](https://github.com/tetratelabs/proxy-wasm-go-sdk/blob/cf6ad74ed58b284d3d8ceeb8c5dba2280d5b1007/proxywasm/vmstate.go#L41-L46).
     - Theoretically, we can implement our own GC algorithms tailored for proxy-wasm through `alloc(uintptr)` [interface](https://github.com/tinygo-org/tinygo/blob/v0.14.1/src/runtime/gc_none.go#L13) 
     with `-gc=none` option. This is the future TODO.
 - `recover` is [not implemented](https://github.com/tinygo-org/tinygo/issues/891) in TinyGo, and there's no way to prevent the WASM virtual machine from aborting.
-- Be careful about using Goroutine
+- Goroutine support
     - In Tinygo, Goroutine is implmeneted through LLVM's coroutine (see [this blog post](https://aykevl.nl/2019/02/tinygo-goroutines)).
-    - Make every goroutine exit as soon as possible, otherwise it will block the proxy's worker thread. That is too bad for processing realtime network requests.
-    - We strongly recommend that you implement the `OnTick` function for any asynchronous task instead of using Goroutine so we do not block requests.
+    - In Envoy, WASM modules are run in the event driven manner, and therefore the "scheduler" is not executed once the main function exits. 
+        That means you cannot have the expected behavior of Goroutine as in ordinary host environments.
+        - The question "How to deal with Goroutine in a thread local WASM VM executed in the event drive manner" has yet to be answered.
+    - We strongly recommend that you implement the `OnTick` function for any asynchronous task instead of using Goroutine.
+    - The scheduler can be disabled with `-scheduler=none` option of TinyGo.
 
 ## references