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Merge #17507: random: mark RandAddPeriodic and SeedPeriodic as noexcept

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55b2cb199c random: mark RandAddPeriodic and SeedPeriodic as noexcept (fanquake)
461e547877 doc: correct random.h docs after #17270 (fanquake)

Pull request description:

  The usage of `MilliSleep()` in SeedPeriodic (previously SeedSleep) was
  [removed](d61f2bb076) in #17270, meaning it, and its users can now be marked `noexcept`.

  This also corrects the docs in random.h for some of the changes in #17270.

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This commit is contained in:
Wladimir J. van der Laan 2019-12-05 15:14:24 +01:00
commit 6fff333c9f
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2 changed files with 12 additions and 22 deletions
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18
src/random.cpp
View file

@ -179,7 +179,7 @@ static uint64_t GetRdSeed() noexcept
/* Access to other hardware random number generators could be added here later,
* assuming it is sufficiently fast (in the order of a few hundred CPU cycles).
* Slower sources should probably be invoked separately, and/or only from
* RandAddSeedSleep (which is called during idle background operation).
* RandAddPeriodic (which is called once a minute).
*/
static void InitHardwareRand() {}
static void ReportHardwareRand() {}
@ -416,17 +416,7 @@ RNGState& GetRNGState() noexcept
/* A note on the use of noexcept in the seeding functions below:
*
* None of the RNG code should ever throw any exception, with the sole exception
* of MilliSleep in SeedSleep, which can (and does) support interruptions which
* cause a boost::thread_interrupted to be thrown.
*
* This means that SeedSleep, and all functions that invoke it are throwing.
* However, we know that GetRandBytes() and GetStrongRandBytes() never trigger
* this sleeping logic, so they are noexcept. The same is true for all the
* GetRand*() functions that use GetRandBytes() indirectly.
*
* TODO: After moving away from interruptible boost-based thread management,
* everything can become noexcept here.
* None of the RNG code should ever throw any exception.
*/
static void SeedTimestamp(CSHA512& hasher) noexcept
@ -498,7 +488,7 @@ static void SeedStrengthen(CSHA512& hasher, RNGState& rng, int microseconds) noe
Strengthen(strengthen_seed, microseconds, hasher);
}
static void SeedPeriodic(CSHA512& hasher, RNGState& rng)
static void SeedPeriodic(CSHA512& hasher, RNGState& rng) noexcept
{
// Everything that the 'fast' seeder includes
SeedFast(hasher);
@ -575,7 +565,7 @@ static void ProcRand(unsigned char* out, int num, RNGLevel level)
void GetRandBytes(unsigned char* buf, int num) noexcept { ProcRand(buf, num, RNGLevel::FAST); }
void GetStrongRandBytes(unsigned char* buf, int num) noexcept { ProcRand(buf, num, RNGLevel::SLOW); }
void RandAddPeriodic() { ProcRand(nullptr, 0, RNGLevel::PERIODIC); }
void RandAddPeriodic() noexcept { ProcRand(nullptr, 0, RNGLevel::PERIODIC); }
void RandAddEvent(const uint32_t event_info) {
LOCK(events_mutex);

16
src/random.h
View file

@ -40,17 +40,17 @@
* These entropy sources are slower, but designed to make sure the RNG state contains
* fresh data that is unpredictable to attackers.
*
* - RandAddSeedSleep() seeds everything that fast seeding includes, but additionally:
* - A high-precision timestamp before and after sleeping 1ms.
* - (On Windows) Once every 10 minutes, performance monitoring data from the OS.
- - Once every minute, strengthen the entropy for 10 ms using repeated SHA512.
* These just exploit the fact the system is idle to improve the quality of the RNG
* slightly.
* - RandAddPeriodic() seeds everything that fast seeding includes, but additionally:
* - A high-precision timestamp
* - Dynamic environment data (performance monitoring, ...)
* - Strengthen the entropy for 10 ms using repeated SHA512.
* This is run once every minute.
*
* On first use of the RNG (regardless of what function is called first), all entropy
* sources used in the 'slow' seeder are included, but also:
* - 256 bits from the hardware RNG (rdseed or rdrand) when available.
* - (On Windows) Performance monitoring data from the OS.
* - Dynamic environment data (performance monitoring, ...)
* - Static environment data
* - Strengthen the entropy for 100 ms using repeated SHA512.
*
* When mixing in new entropy, H = SHA512(entropy || old_rng_state) is computed, and
@ -87,7 +87,7 @@ void GetStrongRandBytes(unsigned char* buf, int num) noexcept;
*
* Thread-safe.
*/
void RandAddPeriodic();
void RandAddPeriodic() noexcept;
/**
* Gathers entropy from the low bits of the time at which events occur. Should