I have the following program:
import os
import posix_utils
import strformat
import threadpool
let tempRootPath = mkdtemp("vppdiff")
proc xmiFilePath(fileNumber: int, cleaned: bool): string =
let cleanedSuffix = "_cleaned"
return tempRootPath / fmt"xmi{fileNumber}{cleanedSuffix}.xmi"
var fv = spawn xmiFilePath(1, false)
echo ^fv
Run
When I try to compile it with Nim 1.0.0, I get
$ nim c --threads:on -r src/gcsafe_example.nim
...
gcsafe_example.nim(13, 27) Error: 'spawn' takes a GC safe call expression
Run
Looking at
[https://nim-lang.org/docs/manual.html#threads-gc-safety](https://nim-lang.org/docs/manual.html#threads-gc-safety)
, this is reasonable. Actually with a {.gcsafe.} block, as in
import os
import posix_utils
import strformat
import threadpool
let tempRootPath = mkdtemp("vppdiff")
proc xmiFilePath(fileNumber: int, cleaned: bool): string =
let cleanedSuffix = "_cleaned"
{.gcsafe.}:
return tempRootPath / fmt"xmi{fileNumber}{cleanedSuffix}.xmi"
var fv = spawn xmiFilePath(1, false)
echo ^fv
Run
the program is compiled and seems to work.
Questions:
* Have a understood the GC safety concept correctly in that this should
_actually_ be safe? My reasoning is that tempRootPath is set once before
xmiFilePath is called, so there shouldn't be any race condition or tempRootPath
going away while xmiFilePath runs. Is this correct?
* Would I get an error or at least a warning if using a {.gcsafe.} block
actually wouldn't be safe?
* If the answer to my first question is "yes", could Nim, maybe in a future
version, recognize by itself that this usage is safe and accept the code
without the {.gcsafe.} usage? _Should_ the compiler do this?
* Is there more documentation on GC safety, for example an article, that
would answer at least the first question? :-)
