From 252439c1af49807826ab58402f84f0cfbcbc9431 Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Wed, 21 Sep 2016 01:59:43 +0300
Subject: [PATCH] Fixed a deadlocking race condition that might happen when
 reading APU memory in the hex viewer

---
 Core/apu.c | 5 ++++-
 Core/gb.h  | 1 +
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/Core/apu.c b/Core/apu.c
index 9bedc5e..4743fcb 100755
--- a/Core/apu.c
+++ b/Core/apu.c
@@ -63,8 +63,9 @@ static int16_t step_lfsr(uint16_t lfsr, bool uses_7_bit)
 
 static void GB_apu_run_internal(GB_gameboy_t *gb)
 {
+    while (!__sync_bool_compare_and_swap(&gb->apu_lock, false, true));
     uint32_t steps = gb->apu.apu_cycles / (CPU_FREQUENCY/APU_FREQUENCY);
-    if (!steps) return;
+    if (!steps) goto exit;
 
     gb->apu.apu_cycles %= (CPU_FREQUENCY/APU_FREQUENCY);
     for (uint8_t i = 0; i < 4; i++) {
@@ -123,6 +124,8 @@ static void GB_apu_run_internal(GB_gameboy_t *gb)
             gb->apu.wave_channels[0].cur_sweep_steps = gb->apu.wave_channels[0].sweep_steps;
         }
     }
+exit:
+    gb->apu_lock = false;
 }
 
 void GB_apu_get_samples_and_update_pcm_regs(GB_gameboy_t *gb, GB_sample_t *samples)
diff --git a/Core/gb.h b/Core/gb.h
index 22ee9fd..9123dc3 100644
--- a/Core/gb.h
+++ b/Core/gb.h
@@ -363,6 +363,7 @@ typedef struct GB_gameboy_s {
     unsigned int audio_position;
     bool audio_stream_started; // detects first copy request to minimize lag
     volatile bool audio_copy_in_progress;
+    volatile bool apu_lock;
 
     /* Callbacks */
     void *user_data;