Give up on mod mutex, not the right tool; Add screenshot to manual

Signed-off-by: falkTX <falktx@falktx.com>

doc/MODDEVICES.md

@@ -8,6 +8,8 @@ This document briefly describes how to use Cardinal with a [MOD device](https://
 It is intended for this documentation to be part of the plugin bundle when installed from the
 [MOD Plugin store](https://pedalboards.moddevices.com/plugins).
 
+![Screenshot](../src/MOD/CardinalFX.lv2/modgui/screenshot.png "Screenshot")
+
 ## Plugin overview
 
 Cardinal is a free and open-source virtual modular synthesizer plugin,.  

include/mutex.hpp

@@ -19,14 +19,6 @@
 
 #include <pthread.h>
 
-#ifdef __MOD_DEVICES__
-#include <linux/futex.h>
-#include <sys/time.h>
-#include <errno.h>
-#include <syscall.h>
-#include <unistd.h>
-#endif
-
 /* replace Rack's mutex with our own custom one, which can do priority inversion. */
 
 namespace rack {
@@ -34,11 +26,7 @@ namespace rack {
 
 struct SharedMutex {
     pthread_mutex_t readLock;
-#ifdef __MOD_DEVICES__
-    int writeLock;
-#else
     pthread_mutex_t writeLock;
-#endif
 
     SharedMutex() noexcept {
         pthread_mutexattr_t attr;
@@ -48,52 +36,28 @@ struct SharedMutex {
         pthread_mutex_init(&readLock, &attr);
         pthread_mutexattr_destroy(&attr);
 
-#ifdef __MOD_DEVICES__
-        writeLock = 1;
-#else
         pthread_mutexattr_t attr2;
         pthread_mutexattr_init(&attr2);
         pthread_mutexattr_setprotocol(&attr2, PTHREAD_PRIO_NONE);
         pthread_mutexattr_settype(&attr2, PTHREAD_MUTEX_NORMAL);
         pthread_mutex_init(&writeLock, &attr2);
         pthread_mutexattr_destroy(&attr2);
-#endif
     }
 
     ~SharedMutex() noexcept {
         pthread_mutex_destroy(&readLock);
-#ifndef __MOD_DEVICES__
         pthread_mutex_destroy(&writeLock);
-#endif
     }
 
     // for std::lock_guard usage, writers lock
     void lock() noexcept {
-#ifdef __MOD_DEVICES__
-        for (;;)
-        {
-            if (__sync_bool_compare_and_swap(&writeLock, 1, 0))
-                return;
-
-            if (syscall(__NR_futex, &writeLock, FUTEX_WAIT_PRIVATE, 0, nullptr, nullptr, 0) != 0)
-            {
-                if (errno != EAGAIN && errno != EINTR)
-                    return;
-            }
-        }
-#else
-        pthread_mutex_lock(&writeLock);
-#endif
         pthread_mutex_lock(&readLock);
+        pthread_mutex_lock(&writeLock);
     }
+
     void unlock() noexcept {
-        pthread_mutex_unlock(&readLock);
-#ifdef __MOD_DEVICES__
-        if (__sync_bool_compare_and_swap(&writeLock, 0, 1))
-            syscall(__NR_futex, &writeLock, FUTEX_WAKE_PRIVATE, 1, nullptr, nullptr, 0);
-#else
         pthread_mutex_unlock(&writeLock);
-#endif
+        pthread_mutex_unlock(&readLock);
     }
 
     // for SharedLock usage, readers lock

src/Makefile.cardinal.mk

@@ -307,7 +307,7 @@ $(TARGET_DIR)/$(NAME).lv2/mod%: ../MOD/$(NAME).lv2/mod%
 	$(SILENT)ln -sf $(abspath $<) $@
 
 $(TARGET_DIR)/$(NAME).lv2/modgui/documentation.pdf: ../../doc/MODDEVICES.md $(TARGET_DIR)/$(NAME).lv2/modgui
-	pandoc $< -o $@
+	(cd ../../doc/ && pandoc MODDEVICES.md -f markdown+implicit_figures -o $(abspath $@))
 endif
 
 $(TARGET_DIR)/$(NAME).vst/resources/%: ../Rack/res/%