rts: Introduce getNumCapabilities

And ensure accesses to n_capabilities are atomic (although with relaxed
ordering). This is necessary as RTS API callers may concurrently call
into the RTS without holding a capability.

1 files changed, 5 insertions, 2 deletions

diff --git a/rts/include/rts/Threads.h b/rts/include/rts/Threads.h
index 9303a9e80d..035e0d0315 100644
--- a/rts/include/rts/Threads.h
+++ b/rts/include/rts/Threads.h
@@ -67,10 +67,13 @@ pid_t  forkProcess     (HsStablePtr *entry)
 HsBool rtsSupportsBoundThreads (void);
 
 // The number of Capabilities.
-// ToDo: I would like this to be private to the RTS and instead expose a
-// function getNumCapabilities(), but it is used in compiler/cbits/genSym.c
+// TODO: Ideally we would only provide getNumCapabilities
+// but this is used in compiler/cbits/genSym.c
 extern unsigned int n_capabilities;
 
+INLINE_HEADER unsigned int getNumCapabilities(void)
+{ return RELAXED_LOAD(&n_capabilities); }
+
 // The number of Capabilities that are not disabled
 extern uint32_t enabled_capabilities;