Allow the number of capabilities to be increased at runtime (#3729)

At present the number of capabilities can only be *increased*, not
decreased.  The latter presents a few more challenges!

2 files changed, 22 insertions, 6 deletions

diff --git a/rts/eventlog/EventLog.c b/rts/eventlog/EventLog.c
index 88fc64010d..af87492876 100644
--- a/rts/eventlog/EventLog.c
+++ b/rts/eventlog/EventLog.c
@@ -254,12 +254,8 @@ initEventLogging(void)
 #else
     n_caps = 1;
 #endif
-    capEventBuf = stgMallocBytes(n_caps * sizeof(EventsBuf),"initEventLogging");
+    moreCapEventBufs(0,n_caps);
 
-    for (c = 0; c < n_caps; ++c) {
-        // Init buffer for events.
-        initEventsBuf(&capEventBuf[c], EVENT_LOG_SIZE, c);
-    }
     initEventsBuf(&eventBuf, EVENT_LOG_SIZE, (EventCapNo)(-1));
 
     // Write in buffer: the header begin marker.
@@ -417,7 +413,26 @@ endEventLogging(void)
     }
 }
 
-void 
+void
+moreCapEventBufs (nat from, nat to)
+{
+    nat c;
+
+    if (from > 0) {
+        capEventBuf = stgReallocBytes(capEventBuf, to * sizeof(EventsBuf),
+                                      "moreCapEventBufs");
+    } else {
+        capEventBuf = stgMallocBytes(to * sizeof(EventsBuf),
+                                     "moreCapEventBufs");
+    }
+
+    for (c = from; c < to; ++c) {
+        initEventsBuf(&capEventBuf[c], EVENT_LOG_SIZE, c);
+    }
+}
+
+
+void
 freeEventLogging(void)
 {
     StgWord8 c;
diff --git a/rts/eventlog/EventLog.h b/rts/eventlog/EventLog.h
index 667f34867d..1858be8ecd 100644
--- a/rts/eventlog/EventLog.h
+++ b/rts/eventlog/EventLog.h
@@ -26,6 +26,7 @@ void endEventLogging(void);
 void freeEventLogging(void);
 void abortEventLogging(void); // #4512 - after fork child needs to abort
 void flushEventLog(void);     // event log inherited from parent
+void moreCapEventBufs (nat from, nat to);
 
 /* 
  * Post a scheduler event to the capability's event buffer (an event