Add `tearDownForeignThreadGc` function (#5369)

tests/gc/foreign_thr.nim

@@ -0,0 +1,88 @@
+discard """
+  output: '''
+Hello from thread
+Hello from thread
+Hello from thread
+Hello from thread
+'''
+  cmd: "nim $target --hints:on --threads:on --tlsEmulation:off $options $file"
+"""
+# Copied from stdlib
+import strutils
+
+const
+  StackGuardSize = 4096
+  ThreadStackMask = 1024*256*sizeof(int)-1
+  ThreadStackSize = ThreadStackMask+1 - StackGuardSize
+
+type ThreadFunc = proc() {.thread.}
+
+when defined(posix):
+  import posix
+
+  proc runInForeignThread(f: ThreadFunc) =
+    proc wrapper(p: pointer): pointer {.noconv.} =
+      let thr = cast[ThreadFunc](p)
+      setupForeignThreadGc()
+      thr()
+      tearDownForeignThreadGc()
+      setupForeignThreadGc()
+      thr()
+      tearDownForeignThreadGc()
+      result = nil
+
+    var attrs {.noinit.}: PthreadAttr
+    doAssert pthread_attr_init(addr attrs) == 0
+    doAssert pthread_attr_setstacksize(addr attrs, ThreadStackSize) == 0
+    var tid: Pthread
+    doAssert pthread_create(addr tid, addr attrs, wrapper, f) == 0
+    doAssert pthread_join(tid, nil) == 0
+
+elif defined(windows):
+  import winlean
+  type
+    WinThreadProc = proc (x: pointer): int32 {.stdcall.}
+
+  proc createThread(lpThreadAttributes: pointer, dwStackSize: DWORD,
+                     lpStartAddress: WinThreadProc,
+                     lpParameter: pointer,
+                     dwCreationFlags: DWORD,
+                     lpThreadId: var DWORD): Handle {.
+    stdcall, dynlib: "kernel32", importc: "CreateThread".}
+
+  proc wrapper(p: pointer): int32 {.stdcall.} =
+    let thr = cast[ThreadFunc](p)
+    setupForeignThreadGc()
+    thr()
+    tearDownForeignThreadGc()
+    setupForeignThreadGc()
+    thr()
+    tearDownForeignThreadGc()
+    result = 0'i32
+
+  proc runInForeignThread(f: ThreadFunc) =
+    var dummyThreadId: DWORD
+    var h = createThread(nil, ThreadStackSize.int32, wrapper.WinThreadProc, cast[pointer](f), 0, dummyThreadId)
+    doAssert h != 0.Handle
+    doAssert waitForSingleObject(h, -1'i32) == 0.DWORD
+
+else:
+  {.fatal: "Unknown system".}
+
+proc runInNativeThread(f: ThreadFunc) =
+  proc wrapper(f: ThreadFunc) {.thread.} =
+    # These operations must be NOP
+    setupForeignThreadGc()
+    tearDownForeignThreadGc()
+    f()
+    f()
+  var thr: Thread[ThreadFunc]
+  createThread(thr, wrapper, f)
+  joinThread(thr)
+
+proc f {.thread.} =
+  var msg = "Hello " & "from thread"
+  echo msg
+
+runInForeignThread(f)
+runInNativeThread(f)

tests/testament/categories.nim

@@ -147,6 +147,7 @@ proc gcTests(r: var TResults, cat: Category, options: string) =
       testSpec r, makeTest("tests/gc" / filename, options &
                     " -d:release --gc:boehm", cat, actionRun)
 
+  testWithoutBoehm "foreign_thr"
   test "gcemscripten"
   test "growobjcrash"
   test "gcbench"