Add read-write mutexes to canvas pixels. New error infrastructure.

1 files changed, 100 insertions, 6 deletions

diff --git a/libdimension/canvas.c b/libdimension/canvas.c
index 21d6d86..e56c391 100644
--- a/libdimension/canvas.c
+++ b/libdimension/canvas.c
@@ -19,34 +19,128 @@
  *************************************************************************/
 
 #include "dimension.h"
-#include <stdlib.h> /* For malloc(), free() */
+#include <pthread.h> /* Must be first included header */
+#include <stdlib.h>  /* For malloc(), free() */
 
 dmnsn_canvas *
 dmnsn_new_canvas(unsigned int x, unsigned int y)
 {
+  unsigned int i, j, k, l;
   dmnsn_canvas *canvas = malloc(sizeof(dmnsn_canvas));
 
   if (canvas) {
     canvas->x = x;
     canvas->y = y;
     canvas->pixels = malloc(sizeof(dmnsn_color)*x*y);
+    if (!canvas->pixels) {
+      free(canvas);
+      return NULL;
+    }
 
-    if (canvas->pixels) {
-      return canvas;
-    } else {
+    canvas->rwlocks = malloc(sizeof(pthread_rwlock_t)*x*y);
+    if (!canvas->rwlocks) {
+      free(canvas->pixels);
       free(canvas);
       return NULL;
     }
-  } else {
-    return NULL;
+
+    for (i = 0; i < x; ++i) {
+      for (j = 0; j < y; ++j) {
+        if (pthread_rwlock_init(&canvas->rwlocks[j*x + i], NULL) != 0) {
+          /* pthread_rwlock_init failed.  Destroy the locks we've already made,
+             free the canvas, and return NULL.  We leak memory if destruction
+             fails (i.e. someone is somehow using an rwlock already). */
+          for (l = 0; l < j; ++l) {
+            for (k = 0; k < x; ++k) {
+              if (pthread_rwlock_destroy(&canvas->rwlocks[l*x + k]) != 0) {
+                /* Low severity, because leaked memory won't actually hurt us */
+                dmnsn_error(DMNSN_SEVERITY_LOW,
+                            "Leaking rwlocks in failed allocation.");
+              }
+            }
+          }
+
+          for (k = 0; k < i; ++k) {
+            if (pthread_rwlock_destroy(&canvas->rwlocks[j*x + k]) != 0) {
+              dmnsn_error(DMNSN_SEVERITY_LOW,
+                          "Leaking rwlocks in failed allocation.");
+            }
+          }
+
+          free(canvas->rwlocks);
+          free(canvas->pixels);
+          free(canvas);
+          return NULL;
+        }
+      }
+    }
   }
+
+  return canvas;
 }
 
 void
 dmnsn_delete_canvas(dmnsn_canvas *canvas)
 {
+  unsigned int i, j;
+
   if (canvas) {
+    for (i = 0; i < canvas->x; ++i) {
+      for (j = 0; j < canvas->y; ++j) {
+        if (pthread_rwlock_destroy(&canvas->rwlocks[j*canvas->x + i]) != 0) {
+              dmnsn_error(DMNSN_SEVERITY_LOW,
+                          "Leaking rwlocks in deallocation.");
+        }
+      }
+    }
+
+    free(canvas->rwlocks);
     free(canvas->pixels);
     free(canvas);
   }
 }
+
+dmnsn_color
+dmnsn_get_pixel(const dmnsn_canvas *canvas, unsigned int x, unsigned int y)
+{
+  dmnsn_color color;
+  dmnsn_rdlock_pixel(canvas, x, y);
+  color = canvas->pixels[y*canvas->x + x];
+  dmnsn_unlock_pixel(canvas, x, y);
+  return color;
+}
+
+void
+dmnsn_set_pixel(dmnsn_canvas *canvas, dmnsn_color color,
+                unsigned int x, unsigned int y)
+{
+  dmnsn_wrlock_pixel(canvas, x, y);
+  canvas->pixels[y*canvas->x + x] = color;
+  dmnsn_unlock_pixel(canvas, x, y);
+}
+
+void
+dmnsn_rdlock_pixel(const dmnsn_canvas *canvas, unsigned int x, unsigned int y)
+{
+  if (pthread_rwlock_rdlock(&canvas->rwlocks[y*canvas->x + x]) != 0) {
+    dmnsn_error(DMNSN_SEVERITY_MEDIUM,
+                "Couldn't acquire read-lock for pixel.");
+  }
+}
+
+void
+dmnsn_wrlock_pixel(dmnsn_canvas *canvas, unsigned int x, unsigned int y)
+{
+  if (pthread_rwlock_wrlock(&canvas->rwlocks[y*canvas->x + x]) != 0) {
+    dmnsn_error(DMNSN_SEVERITY_MEDIUM,
+                "Couldn't acquire write-lock for pixel.");
+  }
+}
+
+void
+dmnsn_unlock_pixel(const dmnsn_canvas *canvas, unsigned int x, unsigned int y)
+{
+  if (pthread_rwlock_unlock(&canvas->rwlocks[y*canvas->x + x]) != 0) {
+    dmnsn_error(DMNSN_SEVERITY_MEDIUM, "Couldn't unlock pixel.");
+  }
+}