zynaddsubfx

commit 0a5445867e602672beb45a2d1517abed414fbe25
parent 8484e6e4fdd6f1816506d17a7fad2f8fd5d927af
Author: Johannes Lorenz <j.git@lorenz-ho.me>
Date:   Sun, 28 Jul 2019 21:48:36 +0200

Master::runOsc(): Fix possible race condition

Fix a race condition when MiddleWare has taken over a dead Master, and
Master just came alive again. In such a case, only one thread does stuff
in Master::runOsc(), the other skips it.

Diffstat:
M
src/Misc/Master.cpp
 | 
51
+++++++++++++++++++++++++++++++++------------------
M
src/Misc/Master.h
 | 
3
+++

2 files changed, 36 insertions(+), 18 deletions(-)
diff --git a/src/Misc/Master.cpp b/src/Misc/Master.cpp
@@ -1123,28 +1123,43 @@ int msg_id=0;
 
 bool Master::runOSC(float *outl, float *outr, bool offline)
 {
-    //Handle user events
-    char loc_buf[1024];
-    DataObj d{loc_buf, 1024, this, bToU};
-    memset(loc_buf, 0, sizeof(loc_buf));
-
-    int events = 0;
-    for(; uToB && uToB->hasNext() && events < 100; ++msg_id, ++events)
+    // the following block is only ever entered by 1 thread at a time
+    // other threads have to ignore it
+    if(!run_osc_in_use.exchange(true)) // exchange returns value before call
     {
-        const char *msg = uToB->read();
-        if(! applyOscEvent(msg, outl, outr, offline, true, d, msg_id) )
-            return false;
-    }
+        /*
+         * WARNING: Do not return without "run_osc_in_use.store(false)"
+         */
 
-    if(automate.damaged) {
-        d.broadcast("/damage", "s", "/automate/");
-        automate.damaged = 0;
-    }
+        //Handle user events
+        char loc_buf[1024];
+        DataObj d{loc_buf, 1024, this, bToU};
+        memset(loc_buf, 0, sizeof(loc_buf));
 
-    if(events>1 && false)
-        fprintf(stderr, "backend: %d events per cycle\n",events);
+        int events = 0;
+        for(; uToB && uToB->hasNext() && events < 100; ++msg_id, ++events)
+        {
+            const char *msg = uToB->read();
+            if(! applyOscEvent(msg, outl, outr, offline, true, d, msg_id,
+                               ) )
+            {
+                run_osc_in_use.store(false);
+                return false;
+            }
+        }
 
-    return true;
+        if(automate.damaged) {
+            d.broadcast("/damage", "s", "/automate/");
+            automate.damaged = 0;
+        }
+
+        if(events>1 && false)
+            fprintf(stderr, "backend: %d events per cycle\n",events);
+
+        run_osc_in_use.store(false);
+        return true;
+    }
+    else { return true; /* = no new master */ }
 }
 
 /*
diff --git a/src/Misc/Master.h b/src/Misc/Master.h
@@ -16,6 +16,7 @@
 #define MASTER_H
 #include "../globals.h"
 #include "Microtonal.h"
+#include <atomic>
 #include <rtosc/automations.h>
 #include <rtosc/savefile.h>
 
@@ -215,6 +216,8 @@ class Master
         uint32_t last_beat = 0;
         uint32_t last_ack = 0;
     private:
+        std::atomic<bool> run_osc_in_use = { false };
+
         float  sysefxvol[NUM_SYS_EFX][NUM_MIDI_PARTS];
         float  sysefxsend[NUM_SYS_EFX][NUM_SYS_EFX];
         int    keyshift;