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1#ifndef TR2_CTR_H
2#define TR2_CTR_H
3
4#include "trace2.h"
5#include "trace2/tr2_tgt.h"
6
7/*
8 * Define a mechanism to allow global "counters".
9 *
10 * Counters can be used count interesting activity that does not fit
11 * the "region and data" model, such as code called from many
12 * different regions and/or where you want to count a number of items,
13 * but don't have control of when the last item will be processed,
14 * such as counter the number of calls to `lstat()`.
15 *
16 * Counters differ from Trace2 "data" events. Data events are emitted
17 * immediately and are appropriate for documenting loop counters at
18 * the end of a region, for example. Counter values are accumulated
19 * during the program and final counter values are emitted at program
20 * exit.
21 *
22 * To make this model efficient, we define a compile-time fixed set of
23 * counters and counter ids using a fixed size "counter block" array
24 * in thread-local storage. This gives us constant time, lock-free
25 * access to each counter within each thread. This lets us avoid the
26 * complexities of dynamically allocating a counter and sharing that
27 * definition with other threads.
28 *
29 * Each thread uses the counter block in its thread-local storage to
30 * increment partial sums for each counter (without locking). When a
31 * thread exits, those partial sums are (under lock) added to the
32 * global final sum.
33 *
34 * Partial sums for each counter are optionally emitted when a thread
35 * exits.
36 *
37 * Final sums for each counter are emitted between the "exit" and
38 * "atexit" events.
39 *
40 * A parallel "counter metadata" table contains the "category" and
41 * "name" fields for each counter. This eliminates the need to
42 * include those args in the various counter APIs.
43 */
44
45/*
46 * The definition of an individual counter as used by an individual
47 * thread (and later in aggregation).
48 */
49struct tr2_counter {
50 uint64_t value;
51};
52
53/*
54 * Metadata for a counter.
55 */
56struct tr2_counter_metadata {
57 const char *category;
58 const char *name;
59
60 /*
61 * True if we should emit per-thread events for this counter
62 * when individual threads exit.
63 */
64 unsigned int want_per_thread_events:1;
65};
66
67/*
68 * A compile-time fixed block of counters to insert into thread-local
69 * storage. This wrapper is used to avoid quirks of C and the usual
70 * need to pass an array size argument.
71 */
72struct tr2_counter_block {
73 struct tr2_counter counter[TRACE2_NUMBER_OF_COUNTERS];
74};
75
76/*
77 * Private routines used by trace2.c to increment a counter for the
78 * current thread.
79 */
80void tr2_counter_increment(enum trace2_counter_id cid, uint64_t value);
81
82/*
83 * Add the current thread's counter data to the global totals.
84 * This is called during thread-exit.
85 *
86 * Caller must be holding the tr2tls_mutex.
87 */
88void tr2_update_final_counters(void);
89
90/*
91 * Emit per-thread counter data for the current thread.
92 * This is called during thread-exit.
93 */
94void tr2_emit_per_thread_counters(tr2_tgt_evt_counter_t *fn_apply);
95
96/*
97 * Emit global counter values.
98 * This is called during atexit handling.
99 *
100 * Caller must be holding the tr2tls_mutex.
101 */
102void tr2_emit_final_counters(tr2_tgt_evt_counter_t *fn_apply);
103
104#endif /* TR2_CTR_H */