--- a/src/hotspot/share/runtime/threadHeapSampler.cpp Wed Oct 03 23:00:32 2018 -0700
+++ b/src/hotspot/share/runtime/threadHeapSampler.cpp Mon Oct 15 14:16:35 2018 -0700
@@ -29,22 +29,29 @@
#include "runtime/sharedRuntime.hpp"
#include "runtime/threadHeapSampler.hpp"
-// Cheap random number generator
+// Cheap random number generator.
uint64_t ThreadHeapSampler::_rnd;
// Default is 512kb.
-int ThreadHeapSampler::_sampling_interval = 512 * 1024;
-int ThreadHeapSampler::_enabled;
+volatile int ThreadHeapSampler::_sampling_interval = 512 * 1024;
+
+// Ordering here is important: _log_table first, _log_table_initialized second.
+double ThreadHeapSampler::_log_table[1 << ThreadHeapSampler::FastLogNumBits] = {};
+
+// Force initialization of the log_table.
+bool ThreadHeapSampler::_log_table_initialized = init_log_table();
-// Statics for the fast log
-static const int FastLogNumBits = 10;
-static const int FastLogMask = (1 << FastLogNumBits) - 1;
-static double log_table[1<<FastLogNumBits]; // Constant
-static bool log_table_initialized;
+bool ThreadHeapSampler::init_log_table() {
+ for (int i = 0; i < (1 << FastLogNumBits); i++) {
+ _log_table[i] = (log(1.0 + static_cast<double>(i+0.5) / (1 << FastLogNumBits))
+ / log(2.0));
+ }
+ return true;
+}
// Returns the next prng value.
// pRNG is: aX+b mod c with a = 0x5DEECE66D, b = 0xB, c = 1<<48
// This is the lrand64 generator.
-static uint64_t next_random(uint64_t rnd) {
+uint64_t ThreadHeapSampler::next_random(uint64_t rnd) {
const uint64_t PrngMult = 0x5DEECE66DLL;
const uint64_t PrngAdd = 0xB;
const uint64_t PrngModPower = 48;
@@ -54,7 +61,7 @@
return (PrngMult * rnd + PrngAdd) & PrngModMask;
}
-static double fast_log2(const double & d) {
+double ThreadHeapSampler::fast_log2(const double& d) {
assert(d>0, "bad value passed to assert");
uint64_t x = 0;
assert(sizeof(d) == sizeof(x),
@@ -64,7 +71,9 @@
assert(FastLogNumBits <= 20, "FastLogNumBits should be less than 20.");
const uint32_t y = x_high >> (20 - FastLogNumBits) & FastLogMask;
const int32_t exponent = ((x_high >> 20) & 0x7FF) - 1023;
- return exponent + log_table[y];
+
+ assert(_log_table_initialized, "log table should be initialized");
+ return exponent + _log_table[y];
}
// Generates a geometric variable with the specified mean (512K by default).
@@ -134,36 +143,6 @@
pick_next_sample(overflow_bytes);
}
-void ThreadHeapSampler::init_log_table() {
- MutexLockerEx mu(ThreadHeapSampler_lock, Mutex::_no_safepoint_check_flag);
-
- if (log_table_initialized) {
- return;
- }
-
- for (int i = 0; i < (1 << FastLogNumBits); i++) {
- log_table[i] = (log(1.0 + static_cast<double>(i+0.5) / (1 << FastLogNumBits))
- / log(2.0));
- }
-
- log_table_initialized = true;
-}
-
-void ThreadHeapSampler::enable() {
- // Done here to be done when things have settled. This adds a mutex lock but
- // presumably, users won't be enabling and disabling all the time.
- init_log_table();
- OrderAccess::release_store(&_enabled, 1);
-}
-
-int ThreadHeapSampler::enabled() {
- return OrderAccess::load_acquire(&_enabled);
-}
-
-void ThreadHeapSampler::disable() {
- OrderAccess::release_store(&_enabled, 0);
-}
-
int ThreadHeapSampler::get_sampling_interval() {
return OrderAccess::load_acquire(&_sampling_interval);
}