diff options
Diffstat (limited to 'src/lib/time')
| -rw-r--r-- | src/lib/time/.may_include | 2 | ||||
| -rw-r--r-- | src/lib/time/compat_time.c | 8 | ||||
| -rw-r--r-- | src/lib/time/compat_time.h | 98 | ||||
| -rw-r--r-- | src/lib/time/include.am | 2 | ||||
| -rw-r--r-- | src/lib/time/time_sys.c | 26 | ||||
| -rw-r--r-- | src/lib/time/time_sys.h | 14 | ||||
| -rw-r--r-- | src/lib/time/tvdiff.c | 3 |
7 files changed, 147 insertions, 6 deletions
diff --git a/src/lib/time/.may_include b/src/lib/time/.may_include index 2c7e37a836..ae01431b60 100644 --- a/src/lib/time/.may_include +++ b/src/lib/time/.may_include @@ -4,8 +4,10 @@ lib/cc/*.h lib/err/*.h lib/intmath/*.h lib/log/*.h +lib/subsys/*.h lib/time/*.h lib/wallclock/*.h +lib/defs/time.h # For load_windows_system_lib. lib/fs/winlib.h
\ No newline at end of file diff --git a/src/lib/time/compat_time.c b/src/lib/time/compat_time.c index 98854bad2c..a047d6c2cd 100644 --- a/src/lib/time/compat_time.c +++ b/src/lib/time/compat_time.c @@ -522,7 +522,9 @@ monotime_init_internal(void) GetTickCount64_fn = (GetTickCount64_fn_t) (void(*)(void)) GetProcAddress(h, "GetTickCount64"); } - // FreeLibrary(h) ? + // We can't call FreeLibrary(h) here, because freeing the handle may + // unload the library, and cause future calls to GetTickCount64_fn() + // to fail. See 29642 for details. } void @@ -787,8 +789,8 @@ monotime_absolute_nsec(void) return monotime_diff_nsec(&initialized_at, &now); } -uint64_t -monotime_absolute_usec(void) +MOCK_IMPL(uint64_t, +monotime_absolute_usec,(void)) { return monotime_absolute_nsec() / 1000; } diff --git a/src/lib/time/compat_time.h b/src/lib/time/compat_time.h index 480d426ac7..2cd4b3bee3 100644 --- a/src/lib/time/compat_time.h +++ b/src/lib/time/compat_time.h @@ -15,6 +15,102 @@ * of tens of milliseconds. */ +/* Q: Should you use monotime or monotime_coarse as your source? + * + * A: Generally, you get better precision with monotime, but better + * performance with monotime_coarse. + * + * Q: Should you use monotime_t or monotime_coarse_t directly? Should you use + * usec? msec? "stamp units?" + * + * A: Using monotime_t and monotime_coarse_t directly is most time-efficient, + * since no conversion needs to happen. But they can potentially use more + * memory than you would need for a usec/msec/"stamp unit" count. + * + * Converting to usec or msec on some platforms, and working with them in + * general, creates a risk of doing a 64-bit division. 64-bit division is + * expensive on 32-bit platforms, which still do exist. + * + * The "stamp unit" type is designed to give a type that is cheap to convert + * from monotime_coarse, has resolution of about 1-2ms, and fits nicely in a + * 32-bit integer. Its downside is that it does not correspond directly + * to a natural unit of time. + * + * There is not much point in using "coarse usec" or "coarse nsec", since the + * current coarse monotime implementations give you on the order of + * milliseconds of precision. + * + * Q: So, what backends is monotime_coarse using? + * + * A: Generally speaking, it uses "whatever monotonic-ish time implemenation + * does not require a context switch." The various implementations provide + * this by having a view of the current time in a read-only memory page that + * is updated with a frequency corresponding to the kernel's tick count. + * + * On Windows, monotime_coarse uses GetCount64() [or GetTickCount() on + * obsolete systems]. MSDN claims that the resolution is "typically in the + * range of 10-16 msec", but it has said that for years. Storing + * monotime_coarse_t uses 8 bytes. + * + * On OSX/iOS, monotime_coarse uses uses mach_approximate_time() where + * available, and falls back to regular monotime. The precision is not + * documented, but the implementation is open-source: it reads from a page + * that the kernel updates. Storing monotime_coarse_t uses 8 bytes. + * + * On unixy systems, monotime_coarse uses clock_gettime() with + * CLOCK_MONOTONIC_COARSE where available, and falls back to CLOCK_MONOTONIC. + * It typically uses vdso tricks to read from a page that the kernel updates. + * Its precision fixed, but you can get it with clock_getres(): on my Linux + * desktop, it claims to be 1 msec, but it will depend on the system HZ + * setting. Storing monotime_coarse_t uses 16 bytes. + * + * [TODO: Try CLOCK_MONOTONIC_FAST on foobsd.] + * + * Q: What backends is regular monotonic time using? + * + * A: In general, regular monotime uses something that requires a system call. + * On platforms where system calls are cheap, you win! Otherwise, you lose. + * + * On Windows, monotonic time uses QuereyPerformanceCounter. Storing + * monotime_t costs 8 bytes. + * + * On OSX/Apple, monotonic time uses mach_absolute_time. Storing + * monotime_t costs 8 bytes. + * + * On unixy systems, monotonic time uses CLOCK_MONOTONIC. Storing + * monotime_t costs 16 bytes. + * + * Q: Tell me about the costs of converting to a 64-bit nsec, usec, or msec + * count. + * + * A: Windows, coarse: Cheap, since it's all multiplication. + * + * Windows, precise: Expensive on 32-bit: it needs 64-bit division. + * + * Apple, all: Expensive on 32-bit: it needs 64-bit division. + * + * Unixy, all: Fairly cheap, since the only division required is dividing + * tv_nsec 1000, and nanoseconds-per-second fits in a 32-bit value. + * + * All, "timestamp units": Cheap everywhere: it never divides. + * + * Q: This is only somewhat related, but how much precision could I hope for + * from a libevent time.? + * + * A: Actually, it's _very_ related if you're timing in order to have a + * timeout happen. + * + * On Windows, it uses select: you could in theory have a microsecond + * resolution, but it usually isn't that accurate. + * + * On OSX, iOS, and BSD, you have kqueue: You could in theory have a nanosecond + * resolution, but it usually isn't that accurate. + * + * On Linux, you have epoll: It has a millisecond resolution. Some recent + * Libevents can also use timerfd for higher resolution if + * EVENT_BASE_FLAG_PRECISE_TIMER is set: Tor doesn't set that flag. + */ + #ifndef TOR_COMPAT_TIME_H #define TOR_COMPAT_TIME_H @@ -103,7 +199,7 @@ uint64_t monotime_absolute_nsec(void); /** * Return the number of microseconds since the timer system was initialized. */ -uint64_t monotime_absolute_usec(void); +MOCK_DECL(uint64_t, monotime_absolute_usec,(void)); /** * Return the number of milliseconds since the timer system was initialized. */ diff --git a/src/lib/time/include.am b/src/lib/time/include.am index a3f93a3744..dae16f49ac 100644 --- a/src/lib/time/include.am +++ b/src/lib/time/include.am @@ -7,6 +7,7 @@ endif src_lib_libtor_time_a_SOURCES = \ src/lib/time/compat_time.c \ + src/lib/time/time_sys.c \ src/lib/time/tvdiff.c src_lib_libtor_time_testing_a_SOURCES = \ @@ -16,4 +17,5 @@ src_lib_libtor_time_testing_a_CFLAGS = $(AM_CFLAGS) $(TEST_CFLAGS) noinst_HEADERS += \ src/lib/time/compat_time.h \ + src/lib/time/time_sys.h \ src/lib/time/tvdiff.h diff --git a/src/lib/time/time_sys.c b/src/lib/time/time_sys.c new file mode 100644 index 0000000000..b3feb7b46a --- /dev/null +++ b/src/lib/time/time_sys.c @@ -0,0 +1,26 @@ +/* Copyright (c) 2018-2019, The Tor Project, Inc. */ +/* See LICENSE for licensing information */ + +/** + * \file time_sys.c + * \brief Subsystem object for monotime setup. + **/ + +#include "orconfig.h" +#include "lib/subsys/subsys.h" +#include "lib/time/time_sys.h" +#include "lib/time/compat_time.h" + +static int +subsys_time_initialize(void) +{ + monotime_init(); + return 0; +} + +const subsys_fns_t sys_time = { + .name = "time", + .level = -90, + .supported = true, + .initialize = subsys_time_initialize, +}; diff --git a/src/lib/time/time_sys.h b/src/lib/time/time_sys.h new file mode 100644 index 0000000000..6a860ffd08 --- /dev/null +++ b/src/lib/time/time_sys.h @@ -0,0 +1,14 @@ +/* Copyright (c) 2018-2019, The Tor Project, Inc. */ +/* See LICENSE for licensing information */ + +/** + * \file time_sys.h + * \brief Declare subsystem object for the time module. + **/ + +#ifndef TOR_TIME_SYS_H +#define TOR_TIME_SYS_H + +extern const struct subsys_fns_t sys_time; + +#endif /* !defined(TOR_TIME_SYS_H) */ diff --git a/src/lib/time/tvdiff.c b/src/lib/time/tvdiff.c index a87d0d96dc..d7c245f57a 100644 --- a/src/lib/time/tvdiff.c +++ b/src/lib/time/tvdiff.c @@ -11,6 +11,7 @@ #include "lib/time/tvdiff.h" #include "lib/cc/compat_compiler.h" +#include "lib/defs/time.h" #include "lib/log/log.h" #ifdef _WIN32 @@ -20,8 +21,6 @@ #include <sys/time.h> #endif -#define TOR_USEC_PER_SEC 1000000 - /** Return the difference between start->tv_sec and end->tv_sec. * Returns INT64_MAX on overflow and underflow. */ |