Specialise evac/scav for single-threaded, not minor, GC
[ghc.git] / rts / sm / GC.h
1 /* -----------------------------------------------------------------------------
2 *
3 * (c) The GHC Team 1998-2006
4 *
5 * Generational garbage collector
6 *
7 * Documentation on the architecture of the Garbage Collector can be
8 * found in the online commentary:
9 *
10 * http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/GC
11 *
12 * ---------------------------------------------------------------------------*/
13
14 #ifndef GC_H
15 #define GC_H
16
17 #include "OSThreads.h"
18
19 /* -----------------------------------------------------------------------------
20 General scheme
21
22 ToDo: move this to the wiki when the implementation is done.
23
24 We're only going to try to parallelise the copying GC for now. The
25 Plan is as follows.
26
27 Each thread has a gc_thread structure (see below) which holds its
28 thread-local data. We'll keep a pointer to this in a thread-local
29 variable, or possibly in a register.
30
31 In the gc_thread structure is a step_workspace for each step. The
32 primary purpose of the step_workspace is to hold evacuated objects;
33 when an object is evacuated, it is copied to the "todo" block in
34 the thread's workspace for the appropriate step. When the todo
35 block is full, it is pushed to the global step->todos list, which
36 is protected by a lock. (in fact we intervene a one-place buffer
37 here to reduce contention).
38
39 A thread repeatedly grabs a block of work from one of the
40 step->todos lists, scavenges it, and keeps the scavenged block on
41 its own ws->scavd_list (this is to avoid unnecessary contention
42 returning the completed buffers back to the step: we can just
43 collect them all later).
44
45 When there is no global work to do, we start scavenging the todo
46 blocks in the workspaces. This is where the scan_bd field comes
47 in: we can scan the contents of the todo block, when we have
48 scavenged the contents of the todo block (up to todo_bd->free), we
49 don't want to move this block immediately to the scavd_list,
50 because it is probably only partially full. So we remember that we
51 have scanned up to this point by saving the block in ws->scan_bd,
52 with the current scan pointer in ws->scan. Later, when more
53 objects have been copied to this block, we can come back and scan
54 the rest. When we visit this workspace again in the future,
55 scan_bd may still be the same as todo_bd, or it might be different:
56 if enough objects were copied into this block that it filled up,
57 then we will have allocated a new todo block, but *not* pushed the
58 old one to the step, because it is partially scanned.
59
60 The reason to leave scanning the todo blocks until last is that we
61 want to deal with full blocks as far as possible.
62 ------------------------------------------------------------------------- */
63
64
65 /* -----------------------------------------------------------------------------
66 Step Workspace
67
68 A step workspace exists for each step for each GC thread. The GC
69 thread takes a block from the todos list of the step into the
70 scanbd and then scans it. Objects referred to by those in the scan
71 block are copied into the todo or scavd blocks of the relevant step.
72
73 ------------------------------------------------------------------------- */
74
75 typedef struct step_workspace_ {
76 step * stp; // the step for this workspace
77 struct gc_thread_ * gct; // the gc_thread that contains this workspace
78
79 // block that is currently being scanned
80 bdescr * scan_bd;
81 StgPtr scan; // the scan pointer
82
83 // where objects to be scavenged go
84 bdescr * todo_bd;
85 StgPtr todo_free; // free ptr for todo_bd
86 StgPtr todo_lim; // lim for todo_bd
87
88 bdescr * buffer_todo_bd; // buffer to reduce contention
89 // on the step's todos list
90
91 // where large objects to be scavenged go
92 bdescr * todo_large_objects;
93
94 // Objects that need not be, or have already been, scavenged.
95 bdescr * scavd_list;
96 lnat n_scavd_blocks; // count of blocks in this list
97
98 } step_workspace;
99
100 /* ----------------------------------------------------------------------------
101 GC thread object
102
103 Every GC thread has one of these. It contains all the step specific
104 workspaces and other GC thread loacl information. At some later
105 point it maybe useful to move this other into the TLS store of the
106 GC threads
107 ------------------------------------------------------------------------- */
108
109 typedef struct gc_thread_ {
110 #ifdef THREADED_RTS
111 OSThreadId id; // The OS thread that this struct belongs to
112 Mutex wake_mutex;
113 Condition wake_cond; // So we can go to sleep between GCs
114 rtsBool wakeup;
115 rtsBool exit;
116 #endif
117 nat thread_index; // a zero based index identifying the thread
118
119 bdescr * free_blocks; // a buffer of free blocks for this thread
120 // during GC without accessing the block
121 // allocators spin lock.
122
123 StgClosure* static_objects; // live static objects
124 StgClosure* scavenged_static_objects; // static objects scavenged so far
125
126 lnat gc_count; // number of gc's this thread has done
127
128 // --------------------
129 // evacuate flags
130
131 step *evac_step; // Youngest generation that objects
132 // should be evacuated to in
133 // evacuate(). (Logically an
134 // argument to evacuate, but it's
135 // static a lot of the time so we
136 // optimise it into a per-thread
137 // variable).
138
139 rtsBool failed_to_evac; // failure to evacuate an object typically
140 // causes it to be recorded in the mutable
141 // object list
142
143 rtsBool eager_promotion; // forces promotion to the evac gen
144 // instead of the to-space
145 // corresponding to the object
146
147 lnat thunk_selector_depth; // ummm.... not used as of now
148
149 #ifdef USE_PAPI
150 int papi_events;
151 #endif
152
153 // -------------------
154 // stats
155
156 lnat copied;
157 lnat any_work;
158 lnat no_work;
159 lnat scav_global_work;
160 lnat scav_local_work;
161
162 // -------------------
163 // workspaces
164
165 // array of workspaces, indexed by stp->abs_no. This is placed
166 // directly at the end of the gc_thread structure so that we can get from
167 // the gc_thread pointer to a workspace using only pointer
168 // arithmetic, no memory access. This happens in the inner loop
169 // of the GC, see Evac.c:alloc_for_copy().
170 step_workspace steps[];
171 } gc_thread;
172
173 extern nat N;
174 extern rtsBool major_gc;
175 extern nat n_gc_threads;
176
177 extern gc_thread **gc_threads;
178 register gc_thread *gct __asm__("%rbx");
179 // extern gc_thread *gct; // this thread's gct TODO: make thread-local
180
181 extern bdescr *mark_stack_bdescr;
182 extern StgPtr *mark_stack;
183 extern StgPtr *mark_sp;
184 extern StgPtr *mark_splim;
185
186 extern rtsBool mark_stack_overflowed;
187 extern bdescr *oldgen_scan_bd;
188 extern StgPtr oldgen_scan;
189
190 extern long copied;
191
192 #ifdef DEBUG
193 extern nat mutlist_MUTVARS, mutlist_MUTARRS, mutlist_MVARS, mutlist_OTHERS;
194 #endif
195
196 StgClosure * isAlive(StgClosure *p);
197
198 #endif /* GC_H */