libraries/base/GHC/TopHandler.hs¶
Note [rts_setMainThread must be called unsafely]¶
rts_setMainThread must be called as unsafe, because it dereferences the Weak# and manipulates the raw Haskell value behind it. Therefore, it must not race with a garbage collection.
Note [rts_setMainThread has an unsound type]¶
‘rts_setMainThread’ is imported with type Weak# ThreadId -> IO (), but this is an unsound type for it: it grabs the /key/ of the ‘Weak#’ object, which isn’t tracked by the type at all. That this works at all is a consequence of the fact that ‘mkWeakThreadId’ produces a ‘Weak#’ with a ‘ThreadId#’ as the key This is fairly robust, in that ‘mkWeakThreadId’ wouldn’t work otherwise, but it still is sufficiently non-trivial to justify an ASSERT in rts/TopHandler.c.
see Note [rts_setMainThread must be called unsafely] and Note [rts_setMainThread has an unsound type]
Note [Disaster with iconv]¶
When using iconv, it’s possible for things like iconv_open to fail in restricted environments (like an initram or restricted container), but when this happens the error raised inevitably calls peekCString, which depends on the users locale, which depends on using iconv_open… which causes an infinite loop.
This occurrence is also known as tickets #10298 and #7695. So to work around it we just set _another_ error handler and bail directly by calling the RTS, without iconv at all.
try to flush stdout/stderr, but don’t worry if we fail (these handles might have errors, and we don’t want to go into an infinite loop).
