much work on the player and hunting for a bug, which first seemed to be in ffmpeg-decoder, but eventually was found in a race condition in audio-placed-player.rkt and an allocation problem in libao-async-ffi-racket.rkt

private/utils.rkt

@@ -38,23 +38,51 @@
   ;; Mutex definitions
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
-  (define (make-mutex)
-  (make-semaphore 1))
+  (define-struct mutex
+    (thread count mut own) #:mutable)
+
+  (define make-mutex-struct make-mutex)
+  
+  (set! make-mutex (λ ()
+                     (make-mutex-struct #f 0 (make-semaphore 1) (make-semaphore 1))))
 
   (define (mutex-lock m)
-    (semaphore-wait m))
+    (semaphore-wait (mutex-own m))
+    (if (eq? (mutex-thread m) (current-thread))
+        (begin
+          (set-mutex-count! m (+ (mutex-count m) 1))
+          (semaphore-post (mutex-own m))
+          )
+        (begin
+          (semaphore-post (mutex-own m))
+          (semaphore-wait (mutex-mut m))
+          (set-mutex-count! m 1)
+          (set-mutex-thread! m (current-thread)))
+        )
+    )
 
   (define (mutex-unlock m)
-    (semaphore-post m))
+    (semaphore-wait (mutex-own m))
+    (let ((count (mutex-count m)))
+      (set! count (- count 1))
+      (set-mutex-count! m count)
+      (if (= count 0)
+          (begin
+            (set-mutex-thread! m #f)
+            (semaphore-post (mutex-own m))
+            (semaphore-post (mutex-mut m)))
+          (semaphore-post (mutex-own m)))
+      )
+    )
 
   (define-syntax with-mutex
     (syntax-rules ()
       ((_ m b1 ...)
        (begin
-         (semaphore-wait m)
-         (let ((r (begin b1 ...)))
-           (semaphore-post m)
-           r)))))
+         (dynamic-wind
+          (λ () (mutex-lock m))
+          (λ () b1 ...)
+          (λ () (mutex-unlock m)))))))
 
 
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;