[Git][ghc/ghc][master] Clarify interruptible FFI wrt masking state

[Marge Bot]

 Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC


Commits:
b57845c3 by Kamil Dworakowski at 2020-11-20T02:09:16-05:00
Clarify interruptible FFI wrt masking state

- - - - -


1 changed file:

- docs/users_guide/exts/ffi.rst


Changes:

=====================================
docs/users_guide/exts/ffi.rst
=====================================
@@ -330,9 +330,10 @@ be annotated with ``interruptible`` instead of ``safe`` or ``unsafe``: ::
        "sleep" sleepBlock :: CUint -> IO CUint
 
 ``interruptible`` behaves exactly as ``safe``, except that when a
-``throwTo`` is directed at a thread in an interruptible foreign call, an
-OS-specific mechanism will be used to attempt to cause the foreign call
-to return:
+``throwTo`` is directed at a thread in an interruptible foreign call,
+irrespective of the masking state, the exception is added to the blocked
+exceptions queue of the target thread and an OS-specific mechanism will be
+used to attempt to cause the foreign call to return:
 
 Unix systems
     The thread making the foreign call is sent a ``SIGPIPE`` signal
@@ -348,7 +349,9 @@ Windows systems
 
 Once the system call is successfully interrupted, the surrounding
 code must return control out of the ``foreign import``, back into Haskell code,
-so that the ``throwTo`` Haskell exception can be raised there.
+so that any blocked exception can be raised if the masking state
+of the thread allows it. Being under mask gives the Haskell code an opportunity
+to detect and react to the interrupt error code from the c call.
 
 If the foreign code simply retries the system call directly without returning
 back to Haskell, then the intended effect of `interruptible` disappears



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/b57845c3d80f5bed8f498f27fb7a318f2b2f8b2c

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/b57845c3d80f5bed8f498f27fb7a318f2b2f8b2c
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