[GHC] #8400: Migrate the RTS to use libuv (or libev, or libevent)

[GHC]

#8400: Migrate the RTS to use libuv (or libev, or libevent)
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        Reporter:  schyler           |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Runtime System    |              Version:
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  635, 7353         |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by dobenour):

 I have an idea for how to implement this:

 * Each `Capability` contains a `uv_loop_t` as well as a pointer to a list
 of threads that are blocked waiting on C callbacks to fire.  Since
 initializing a `uv_loop_t` can fail due to OS resource exhaustion, such as
 too many open files, the RTS checks that initializing succeeded before a
 capability can run Haskell code.
 * Each Capability owns a pool of C structures

   {{{#!C
   typedef struct StgCCallbackInfo {
     StgTSO *BlockedThread; /* The thread that is blocked waiting for the
 callback */
     StgWord refcount;      /* Reference count */
     void *user;            /* Arbitrary C data */
   } StgCCallbackInfo;
   }}}

   This list is a GC root.  The members of this pool are in pinned memory,
 so they can safely be referenced by C code

 * The RTS exports C functions
   {{{#!C
   /**
    * Allocates a C callback info struct, or NULL if we run out of memory.
    */
   StgCCallbackInfo *rts_newCCallbackInfo(Capability *c, StgTSO *t, void
 *user);
   /**
    * Wakes up the thread pointed to by the given `StgCCallbackInfo`.
    */
   void rts_wakeupThread(struct StgCCallbackInfo *ptr);
   /**
    * Increments the reference count on the `StgCCallbackInfo`.
    */
   void rts_callback_incref(struct StgCCallbackInfo *ptr);
   /**
    * Decrements the reference count.
    */
   void rts_callback_decref(struct StgCCallbackInfo *ptr);
   }}}

   which can be used to manipulate these structures

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8400#comment:24>
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