diff options
author | Marshall Clow <mclow@qualcomm.com> | 2011-07-20 19:04:39 +0400 |
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committer | Marshall Clow <mclow@qualcomm.com> | 2011-07-20 19:04:39 +0400 |
commit | e2dcb75b2e4b86b4529e6727571813552718ac19 (patch) | |
tree | d045464a89a3998e769bb3646fc48b9d74852134 /libcxxabi/src/fallback_malloc.cpp | |
parent | 1df50ca6a2f60b3b60ca6adc1ab98f33184c3597 (diff) |
Memory manangement routines for exception objects
llvm-svn: 135587
Diffstat (limited to 'libcxxabi/src/fallback_malloc.cpp')
-rw-r--r-- | libcxxabi/src/fallback_malloc.cpp | 161 |
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 +} |