Memory manangement routines for exception objects

llvm-svn: 135587

1 files changed, 161 insertions, 0 deletions

diff --git a/libcxxabi/src/fallback_malloc.cpp b/libcxxabi/src/fallback_malloc.cpp
new file mode 100644
index 000000000000..45d52fec72fb
--- /dev/null
+++ b/libcxxabi/src/fallback_malloc.cpp
@@ -0,0 +1,161 @@
+//  A small, simple heap manager based (loosely) on the startup heap
+//  based on the startup heap manager from FreeBSD.
+//
+//  Manages a fixed-size memory pool, supports malloc and free only.
+//  No support for realloc.
+//
+//  Allocates chunks in multiples of four bytes, with a four byte header
+//  for each chunk. The overhead of each chunk is kept low by keeping pointers
+//  as two byte offsets within the heap, rather than (4 or 8 byte) pointers.
+
+namespace {
+
+static pthread_mutex_t heap_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+class mutexor {
+public:
+    mutexor ( pthread_mutex_t *m ) : mtx_(m) { pthread_mutex_lock ( mtx_ ); }
+    ~mutexor () { pthread_mutex_unlock ( mtx_ ); }
+private:
+    mutexor ( const mutexor &rhs );
+    mutexor & operator = ( const mutexor &rhs );
+    pthread_mutex_t *mtx_;
+    };
+
+        
+#define HEAP_SIZE   512
+char heap [ HEAP_SIZE ];
+
+typedef unsigned short heap_offset;
+typedef unsigned short heap_size;
+
+struct heap_node {
+    heap_offset next_node;  // offset into heap
+    heap_size   len;        // size in units of "sizeof(heap_node)"
+};
+
+static const heap_node *list_end = (heap_node *) ( &heap [ HEAP_SIZE ] );   // one past the end of the heap
+static heap_node *freelist = NULL;
+
+heap_node *node_from_offset ( const heap_offset offset ) throw() 
+    { return (heap_node *) ( heap + ( offset * sizeof (heap_node))); }
+
+heap_offset offset_from_node ( const heap_node *ptr )    throw() 
+    { return (((char *) ptr ) - heap)  / sizeof (heap_node); }
+ 
+void init_heap () throw() {
+    freelist = (heap_node *) heap;
+    freelist->next_node = offset_from_node ( list_end );
+    freelist->len = HEAP_SIZE / sizeof (heap_node);
+    }
+    
+//  How big a chunk we allocate
+size_t alloc_size (size_t len) throw() 
+    { return (len + sizeof(heap_node) - 1) / sizeof(heap_node) + 1; }
+
+bool is_fallback_ptr ( void *ptr ) throw() 
+    { return ptr >= heap && ptr < ( heap + HEAP_SIZE ); }
+
+void *fallback_malloc(size_t len) throw() {
+    heap_node *p, *prev;
+    const size_t nelems = alloc_size ( len );
+    mutexor mtx ( &heap_mutex );
+    
+    if ( NULL == freelist )
+        init_heap ();
+
+//  Walk the free list, looking for a "big enough" chunk
+    for (p = freelist, prev = 0; 
+            p && p != list_end;     prev = p, p = node_from_offset ( p->next_node)) {
+
+        if (p->len > nelems) {  //  chunk is larger, shorten, and return the tail
+            heap_node *q;
+            
+            p->len -= nelems;
+            q = p + p->len;
+            q->next_node = 0;
+            q->len = nelems;
+            return (void *) (q + 1);
+        }
+        
+        if (p->len == nelems) { // exact size match
+            if (prev == 0)
+                freelist = node_from_offset(p->next_node);
+            else
+                prev->next_node = p->next_node;
+            p->next_node = 0;
+            return (void *) (p + 1);
+        }
+    }
+    return NULL;    // couldn't find a spot big enough
+}
+
+//  Return the start of the next block
+heap_node *after ( struct heap_node *p ) throw() { return p + p->len; }
+
+void fallback_free (void *ptr) throw() {
+    struct heap_node *cp = ((struct heap_node *) ptr) - 1;      // retrieve the chunk
+    struct heap_node *p, *prev;
+
+    mutexor mtx ( &heap_mutex );
+
+#ifdef DEBUG_FALLBACK_MALLOC
+        std::cout << "Freeing item at " << offset_from_node ( cp ) << " of size " << cp->len << std::endl;
+#endif
+
+    for (p = freelist, prev = 0; 
+            p && p != list_end;     prev = p, p = node_from_offset (p->next_node)) {
+#ifdef DEBUG_FALLBACK_MALLOC
+        std::cout << "  p, cp, after (p), after(cp) "
+            << offset_from_node ( p ) << ' '
+            << offset_from_node ( cp ) << ' '
+            << offset_from_node ( after ( p )) << ' '
+            << offset_from_node ( after ( cp )) << std::endl;
+#endif
+        if ( after ( p ) == cp ) {
+#ifdef DEBUG_FALLBACK_MALLOC
+            std::cout << "  Appending onto chunk at " << offset_from_node ( p ) << std::endl;
+#endif
+            p->len += cp->len;  // make the free heap_node larger
+            return;
+            }
+        else if ( after ( cp ) == p ) { // there's a free heap_node right after
+#ifdef DEBUG_FALLBACK_MALLOC
+            std::cout << "  Appending free chunk at " << offset_from_node ( p ) << std::endl;
+#endif
+            cp->len += p->len;
+            if ( prev == 0 ) {
+                freelist = cp;
+                cp->next_node = p->next_node;
+                }
+            else
+                prev->next_node = offset_from_node(cp);
+            return;
+            }
+        }
+//  Nothing to merge with, add it to the start of the free list
+#ifdef DEBUG_FALLBACK_MALLOC
+            std::cout << "  Making new free list entry " << offset_from_node ( cp ) << std::endl;
+#endif
+    cp->next_node = offset_from_node ( freelist );
+    freelist = cp;
+}
+
+#ifdef INSTRUMENT_FALLBACK_MALLOC
+size_t print_free_list () {
+    struct heap_node *p, *prev;
+    heap_size total_free = 0;
+    if ( NULL == freelist )
+        init_heap ();
+    
+    for (p = freelist, prev = 0; 
+            p && p != list_end;     prev = p, p = node_from_offset (p->next_node)) {
+        std::cout << ( prev == 0 ? "" : "  ")  << "Offset: " << offset_from_node ( p ) 
+                << "\tsize: " << p->len << " Next: " << p->next_node << std::endl;
+        total_free += p->len;
+        }
+    std::cout << "Total Free space: " << total_free << std::endl;
+    return total_free;
+    }
+#endif
+}