/* Compact the buffer by trying both shrinking and moving. * * Try to move first. If unsuccesfull, try to shrink. If that was successful * try to move once more as there might be more room now. */ static bool buflib_compact_and_shrink(struct buflib_context *ctx, unsigned shrink_hints) { bool result = false; /* if something compacted before already there will be no further gain */ if (!ctx->compact) result = buflib_compact(ctx); if (!result) { union buflib_data* this; for(this = ctx->buf_start; this < ctx->alloc_end; this += abs(this->val)) { if (this->val > 0 && this[2].ops && this[2].ops->shrink_callback) { int ret; int handle = ctx->handle_table - this[1].handle; char* data = this[1].handle->alloc; ret = this[2].ops->shrink_callback(handle, shrink_hints, data, (char*)(this+this->val)-data); result |= (ret == BUFLIB_CB_OK); /* this might have changed in the callback (if * it shrinked from the top), get it again */ this = handle_to_block(ctx, handle); } } /* shrinking was successful at least once, try compaction again */ if (result) result |= buflib_compact(ctx); } return result; }
/* Compact the buffer by trying both shrinking and moving. * * Try to move first. If unsuccesfull, try to shrink. If that was successful * try to move once more as there might be more room now. */ static bool buflib_compact_and_shrink(struct buflib_context *ctx, unsigned shrink_hints) { bool result = false; /* if something compacted before already there will be no further gain */ if (!ctx->compact) result = buflib_compact(ctx); if (!result) { union buflib_data *this, *before; for(this = ctx->buf_start, before = this; this < ctx->alloc_end; before = this, this += abs(this->val)) { if (this->val > 0 && this[2].ops && this[2].ops->shrink_callback) { int ret; int handle = ctx->handle_table - this[1].handle; char* data = this[1].handle->alloc; bool last = (this+this->val) == ctx->alloc_end; unsigned pos_hints = shrink_hints & BUFLIB_SHRINK_POS_MASK; /* adjust what we ask for if there's free space in the front * this isn't too unlikely assuming this block is * shrinkable but not movable */ if (pos_hints == BUFLIB_SHRINK_POS_FRONT && before != this && before->val < 0) { size_t free_space = (-before->val) * sizeof(union buflib_data); size_t wanted = shrink_hints & BUFLIB_SHRINK_SIZE_MASK; if (wanted < free_space) /* no shrink needed? */ continue; wanted -= free_space; shrink_hints = pos_hints | wanted; } ret = this[2].ops->shrink_callback(handle, shrink_hints, data, (char*)(this+this->val)-data); result |= (ret == BUFLIB_CB_OK); /* 'this' might have changed in the callback (if it shrinked * from the top or even freed the handle), get it again */ this = handle_to_block(ctx, handle); /* The handle was possibly be freed in the callback, * re-run the loop with the handle before */ if (!this) this = before; /* could also change with shrinking from back */ else if (last) ctx->alloc_end = this + this->val; } } /* shrinking was successful at least once, try compaction again */ if (result) result |= buflib_compact(ctx); } return result; }
/* Shift buffered items up by size bytes, or as many as possible if size == 0. * Set size to the number of bytes freed. */ void* buflib_buffer_out(struct buflib_context *ctx, size_t *size) { if (!ctx->compact) buflib_compact(ctx); size_t avail = ctx->last_handle - ctx->alloc_end; size_t avail_b = avail * sizeof(union buflib_data); if (*size && *size < avail_b) { avail = (*size + sizeof(union buflib_data) - 1) / sizeof(union buflib_data); avail_b = avail * sizeof(union buflib_data); } *size = avail_b; void *ret = ctx->buf_start; buflib_buffer_shift(ctx, avail); return ret; }
/* Return the maximum allocatable contiguous memory in bytes */ size_t buflib_allocatable(struct buflib_context* ctx) { union buflib_data *this; size_t free_space = 0, max_free_space = 0; /* make sure buffer is as contiguous as possible */ if (!ctx->compact) buflib_compact(ctx); /* now look if there's free in holes */ for(this = find_first_free(ctx); this < ctx->alloc_end; this += abs(this->val)) { if (this->val < 0) { free_space += -this->val; continue; } /* an unmovable section resets the count as free space * can't be contigous */ if (!IS_MOVABLE(this)) { if (max_free_space < free_space) max_free_space = free_space; free_space = 0; } } /* select the best */ max_free_space = MAX(max_free_space, free_space); max_free_space *= sizeof(union buflib_data); max_free_space = MAX(max_free_space, free_space_at_end(ctx)); if (max_free_space > 0) return max_free_space; else return 0; }
int buflib_alloc_ex(struct buflib_context *ctx, size_t size, const char *name, struct buflib_callbacks *ops) { /* busy wait if there's a thread owning the lock */ while (ctx->handle_lock != 0) YIELD(); union buflib_data *handle, *block; size_t name_len = name ? B_ALIGN_UP(strlen(name)+1) : 0; bool last; /* This really is assigned a value before use */ int block_len; size += name_len; size = (size + sizeof(union buflib_data) - 1) / sizeof(union buflib_data) /* add 4 objects for alloc len, pointer to handle table entry and * name length, and the ops pointer */ + 4; handle_alloc: handle = handle_alloc(ctx); if (!handle) { /* If allocation has failed, and compaction has succeded, it may be * possible to get a handle by trying again. */ if (!ctx->compact && buflib_compact(ctx)) goto handle_alloc; else { /* first try to shrink the alloc before the handle table * to make room for new handles */ int handle = ctx->handle_table - ctx->last_handle; union buflib_data* last_block = handle_to_block(ctx, handle); struct buflib_callbacks* ops = last_block[2].ops; if (ops && ops->shrink_callback) { char *data = buflib_get_data(ctx, handle); unsigned hint = BUFLIB_SHRINK_POS_BACK | 10*sizeof(union buflib_data); if (ops->shrink_callback(handle, hint, data, (char*)(last_block+last_block->val)-data) == BUFLIB_CB_OK) { /* retry one more time */ goto handle_alloc; } } return 0; } } buffer_alloc: /* need to re-evaluate last before the loop because the last allocation * possibly made room in its front to fit this, so last would be wrong */ last = false; for (block = ctx->first_free_block;;block += block_len) { /* If the last used block extends all the way to the handle table, the * block "after" it doesn't have a header. Because of this, it's easier * to always find the end of allocation by saving a pointer, and always * calculate the free space at the end by comparing it to the * last_handle pointer. */ if(block == ctx->alloc_end) { last = true; block_len = ctx->last_handle - block; if ((size_t)block_len < size) block = NULL; break; } block_len = block->val; /* blocks with positive length are already allocated. */ if(block_len > 0) continue; block_len = -block_len; /* The search is first-fit, any fragmentation this causes will be * handled at compaction. */ if ((size_t)block_len >= size) break; } if (!block) { /* Try compacting if allocation failed */ if (buflib_compact_and_shrink(ctx, (size*sizeof(union buflib_data))&BUFLIB_SHRINK_SIZE_MASK)) { goto buffer_alloc; } else { handle->val=1; handle_free(ctx, handle); return 0; } } /* Set up the allocated block, by marking the size allocated, and storing * a pointer to the handle. */ union buflib_data *name_len_slot; block->val = size; block[1].handle = handle; block[2].ops = ops ?: &default_callbacks; strcpy(block[3].name, name); name_len_slot = (union buflib_data*)B_ALIGN_UP(block[3].name + name_len); name_len_slot->val = 1 + name_len/sizeof(union buflib_data); handle->alloc = (char*)(name_len_slot + 1); /* If we have just taken the first free block, the next allocation search * can save some time by starting after this block. */ if (block == ctx->first_free_block) ctx->first_free_block += size; block += size; /* alloc_end must be kept current if we're taking the last block. */ if (last) ctx->alloc_end = block; /* Only free blocks *before* alloc_end have tagged length. */ else if ((size_t)block_len > size) block->val = size - block_len; /* Return the handle index as a positive integer. */ return ctx->handle_table - handle; }