1/*
2 * libwebsockets - small server side websockets and web server implementation
3 *
4 * Copyright (C) 2010 - 2019 Andy Green <andy@warmcat.com>
5 *
6 * Permission is hereby granted, free of charge, to any person obtaining a copy
7 * of this software and associated documentation files (the "Software"), to
8 * deal in the Software without restriction, including without limitation the
9 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
10 * sell copies of the Software, and to permit persons to whom the Software is
11 * furnished to do so, subject to the following conditions:
12 *
13 * The above copyright notice and this permission notice shall be included in
14 * all copies or substantial portions of the Software.
15 *
16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
21 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
22 * IN THE SOFTWARE.
23 */
24
25/*
26 * lws_dsh (Disordered Shared Heap) is an opaque abstraction supporting a single
27 * linear buffer (overallocated at end of the lws_dsh_t) which may contain
28 * multiple kinds of packets that are retired out of order, and tracked by kind.
29 *
30 * Each kind of packet has an lws_dll2 list of its kind of packets and acts as
31 * a FIFO; packets of a particular type are always retired in order. But there
32 * is no requirement about the order types are retired matching the original
33 * order they arrived.
34 *
35 * Gaps are tracked as just another kind of "packet" list.
36 *
37 * "allocations" (including gaps) are prepended by an lws_dsh_object_t.
38 *
39 * dsh may themselves be on an lws_dll2_owner list, and under memory pressure
40 * allocate into other buffers on the list.
41 *
42 * All management structures exist inside the allocated buffer.
43 */
44
45/**
46 * lws_dsh_create() - Allocate a DSH buffer
47 *
48 * \param owner: the owning list this dsh belongs on, or NULL if standalone
49 * \param buffer_size: the allocation in bytes
50 * \param count_kinds: how many separately-tracked fifos use the buffer
51 *
52 * This makes a single heap allocation that includes internal tracking objects
53 * in the buffer. Sub-allocated objects are bound to a "kind" index and
54 * managed via a FIFO for each kind.
55 *
56 * Every "kind" of allocation shares the same buffer space.
57 *
58 * Multiple buffers may be bound together in an lws_dll2 list, and if an
59 * allocation cannot be satisfied by the local buffer, space can be borrowed
60 * from other dsh in the same list (the local dsh FIFO tracks these "foreign"
61 * allocations as if they were local).
62 *
63 * Returns an opaque pointer to the dsh, or NULL if allocation failed.
64 */
65LWS_VISIBLE LWS_EXTERN struct lws_dsh *
66lws_dsh_create(lws_dll2_owner_t *owner, size_t buffer_size, int count_kinds);
67
68/**
69 * lws_dsh_destroy() - Destroy a DSH buffer
70 *
71 * \param pdsh: pointer to the dsh pointer
72 *
73 * Deallocates the DSH and sets *pdsh to NULL.
74 *
75 * Before destruction, any foreign buffer usage on the part of this dsh are
76 * individually freed. All dsh on the same list are walked and checked if they
77 * have their own foreign allocations on the dsh buffer being destroyed. If so,
78 * it attempts to migrate the allocation to a dsh that is not currently being
79 * destroyed. If all else fails (basically the buffer memory is being shrunk)
80 * unmigratable objects are cleanly destroyed.
81 */
82LWS_VISIBLE LWS_EXTERN void
83lws_dsh_destroy(struct lws_dsh **pdsh);
84
85/**
86 * lws_dsh_alloc_tail() - make a suballocation inside a dsh
87 *
88 * \param dsh: the dsh tracking the allocation
89 * \param kind: the kind of allocation
90 * \param src1: the first source data to copy
91 * \param size1: the size of the first source data
92 * \param src2: the second source data to copy (after the first), or NULL
93 * \param size2: the size of the second source data
94 *
95 * Allocates size1 + size2 bytes in a dsh (it prefers the given dsh but will
96 * borrow space from other dsh on the same list if necessary) and copies size1
97 * bytes into it from src1, followed by size2 bytes from src2 if src2 isn't
98 * NULL. The actual suballocation is a bit larger because of alignment and a
99 * prepended management header.
100 *
101 * The suballocation is added to the kind-specific FIFO at the tail.
102 */
103LWS_VISIBLE LWS_EXTERN int
104lws_dsh_alloc_tail(struct lws_dsh *dsh, int kind, const void *src1,
105 size_t size1, const void *src2, size_t size2);
106
107/**
108 * lws_dsh_free() - free a suballocation from the dsh
109 *
110 * \param obj: a pointer to a void * that pointed to the allocated payload
111 *
112 * This returns the space used by \p obj in the dsh buffer to the free list
113 * of the dsh the allocation came from.
114 */
115LWS_VISIBLE LWS_EXTERN void
116lws_dsh_free(void **obj);
117
118LWS_VISIBLE LWS_EXTERN size_t
119lws_dsh_get_size(struct lws_dsh *dsh, int kind);
120
121/**
122 * lws_dsh_get_head() - get the head allocation inside the dsh
123 *
124 * \param dsh: the dsh tracking the allocation
125 * \param kind: the kind of allocation
126 * \param obj: pointer to a void * to be set to the payload
127 * \param size: set to the size of the allocation
128 *
129 * This gets the "next" object in the kind FIFO for the dsh, and returns 0 if
130 * any. If none, returns nonzero.
131 *
132 * This is nondestructive of the fifo or the payload. Use lws_dsh_free on
133 * obj to remove the entry from the kind fifo and return the payload to the
134 * free list.
135 */
136LWS_VISIBLE LWS_EXTERN int
137lws_dsh_get_head(struct lws_dsh *dsh, int kind, void **obj, size_t *size);
138
139/**
140 * lws_dsh_describe() - DEBUG BUILDS ONLY dump the dsh to the logs
141 *
142 * \param dsh: the dsh to dump
143 * \param desc: text that appears at the top of the dump
144 *
145 * Useful information for debugging lws_dsh
146 */
147LWS_VISIBLE LWS_EXTERN void
148lws_dsh_describe(struct lws_dsh *dsh, const char *desc);
149