blob: b821e34047aed5e9e77415ff9e4282fc2c176a46 (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
|
#pragma once
// Rseq is available on Linux for the arches where we can read the thread pointer.
// Consumers must guard rseq usage with this macro.
#if defined(__linux__) && (defined(__x86_64__) || defined(__aarch64__))
#define YT_RSEQ_AVAILABLE
#endif
namespace NYT::NRseq {
////////////////////////////////////////////////////////////////////////////////
//! Returns whether the per-CPU rseq fast path is safe to use in this process.
/*!
* The fast path reads the rseq area at a thread-pointer offset cached at startup, which is
* sound only when __rseq_abi sits at a fixed offset from the thread pointer (a glibc-owned
* area or the static TLS block, incl. tcmalloc) -- not when it lands in a dlopen'd module's
* dynamically allocated TLS. Returns false there (and where there is no fast path) so callers
* fall back to atomics. Decided once on a spawned thread and cached: one spawn at first use.
*/
bool IsPerCpuFastPathSupported();
////////////////////////////////////////////////////////////////////////////////
} // namespace NYT::NRseq
#ifdef YT_RSEQ_AVAILABLE
#include <cstddef>
namespace NYT::NRseq {
////////////////////////////////////////////////////////////////////////////////
//! Byte offset from the thread pointer to the rseq area's cpu_id field (glibc's area when
//! glibc registers rseq, otherwise our own). A fixed offset across threads only when the area
//! is glibc-owned or in the static TLS block; #IsPerCpuFastPathSupported probes this and gates the
//! fast path. NB: 0 until our startup initializer runs, but nothing reads rseq before then.
extern std::ptrdiff_t CpuIdFieldOffset;
//! Reads a field of the calling thread's rseq area at the given offset from the thread
//! pointer. Branch-free and force-inlined.
//!
//! WARNING (fiber TLS): reads the thread pointer, so it must be reached only through a
//! non-inlinable, fiber-switch-free frame (YT_PREVENT_TLS_CACHING, see library/cpp/yt/misc/tls.h).
template <class T>
T ReadField(std::ptrdiff_t fieldOffset);
//! Registers the calling thread with rseq if we own the registration and it is not
//! registered yet. Returns false if rseq is unavailable (no kernel support). Cheap
//! once registered.
bool EnsureCurrentThreadRegistered();
////////////////////////////////////////////////////////////////////////////////
} // namespace NYT::NRseq
#define RSEQ_INL_H_
#include "rseq-inl.h"
#undef RSEQ_INL_H_
#endif // YT_RSEQ_AVAILABLE
|
