--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/runtime/threadHeapSampler.cpp Fri Jun 15 02:31:37 2018 -0700
@@ -0,0 +1,188 @@
+/*
+ * Copyright (c) 2018, Google and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "runtime/handles.inline.hpp"
+#include "runtime/orderAccess.hpp"
+#include "runtime/sharedRuntime.hpp"
+#include "runtime/threadHeapSampler.hpp"
+
+// Cheap random number generator
+uint64_t ThreadHeapSampler::_rnd;
+// Default is 512kb.
+int ThreadHeapSampler::_sampling_rate = 512 * 1024;
+int ThreadHeapSampler::_enabled;
+
+// 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;
+
+// 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) {
+ const uint64_t PrngMult = 0x5DEECE66DLL;
+ const uint64_t PrngAdd = 0xB;
+ const uint64_t PrngModPower = 48;
+ const uint64_t PrngModMask = right_n_bits(PrngModPower);
+ //assert(IS_SAFE_SIZE_MUL(PrngMult, rnd), "Overflow on multiplication.");
+ //assert(IS_SAFE_SIZE_ADD(PrngMult * rnd, PrngAdd), "Overflow on addition.");
+ return (PrngMult * rnd + PrngAdd) & PrngModMask;
+}
+
+static double fast_log2(const double & d) {
+ assert(d>0, "bad value passed to assert");
+ uint64_t x = 0;
+ assert(sizeof(d) == sizeof(x),
+ "double and uint64_t do not have the same size");
+ x = *reinterpret_cast<const uint64_t*>(&d);
+ const uint32_t x_high = x >> 32;
+ 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];
+}
+
+// Generates a geometric variable with the specified mean (512K by default).
+// This is done by generating a random number between 0 and 1 and applying
+// the inverse cumulative distribution function for an exponential.
+// Specifically: Let m be the inverse of the sample rate, then
+// the probability distribution function is m*exp(-mx) so the CDF is
+// p = 1 - exp(-mx), so
+// q = 1 - p = exp(-mx)
+// log_e(q) = -mx
+// -log_e(q)/m = x
+// log_2(q) * (-log_e(2) * 1/m) = x
+// In the code, q is actually in the range 1 to 2**26, hence the -26 below
+void ThreadHeapSampler::pick_next_geometric_sample() {
+ _rnd = next_random(_rnd);
+ // Take the top 26 bits as the random number
+ // (This plus a 1<<58 sampling bound gives a max possible step of
+ // 5194297183973780480 bytes. In this case,
+ // for sample_parameter = 1<<19, max possible step is
+ // 9448372 bytes (24 bits).
+ const uint64_t PrngModPower = 48; // Number of bits in prng
+ // The uint32_t cast is to prevent a (hard-to-reproduce) NAN
+ // under piii debug for some binaries.
+ double q = static_cast<uint32_t>(_rnd >> (PrngModPower - 26)) + 1.0;
+ // Put the computed p-value through the CDF of a geometric.
+ // For faster performance (save ~1/20th exec time), replace
+ // min(0.0, FastLog2(q) - 26) by (Fastlog2(q) - 26.000705)
+ // The value 26.000705 is used rather than 26 to compensate
+ // for inaccuracies in FastLog2 which otherwise result in a
+ // negative answer.
+ double log_val = (fast_log2(q) - 26);
+ double result =
+ (0.0 < log_val ? 0.0 : log_val) * (-log(2.0) * (get_sampling_rate())) + 1;
+ assert(result > 0 && result < SIZE_MAX, "Result is not in an acceptable range.");
+ size_t rate = static_cast<size_t>(result);
+ _bytes_until_sample = rate;
+}
+
+void ThreadHeapSampler::pick_next_sample(size_t overflowed_bytes) {
+ if (get_sampling_rate() == 1) {
+ _bytes_until_sample = 1;
+ return;
+ }
+
+ pick_next_geometric_sample();
+
+ // Try to correct sample size by removing extra space from last allocation.
+ if (overflowed_bytes > 0 && _bytes_until_sample > overflowed_bytes) {
+ _bytes_until_sample -= overflowed_bytes;
+ }
+}
+
+void ThreadHeapSampler::check_for_sampling(HeapWord* ptr, size_t allocation_size, size_t bytes_since_allocation) {
+ oopDesc* oop = reinterpret_cast<oopDesc*>(ptr);
+ size_t total_allocated_bytes = bytes_since_allocation + allocation_size;
+
+ // If not yet time for a sample, skip it.
+ if (total_allocated_bytes < _bytes_until_sample) {
+ _bytes_until_sample -= total_allocated_bytes;
+ return;
+ }
+
+ JvmtiExport::sampled_object_alloc_event_collector(oop);
+
+ size_t overflow_bytes = total_allocated_bytes - _bytes_until_sample;
+ 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_rate() {
+ return OrderAccess::load_acquire(&_sampling_rate);
+}
+
+void ThreadHeapSampler::set_sampling_rate(int sampling_rate) {
+ OrderAccess::release_store(&_sampling_rate, sampling_rate);
+}
+
+// Methods used in assertion mode to check if a collector is present or not at
+// the moment of TLAB sampling, ie a slow allocation path.
+bool ThreadHeapSampler::sampling_collector_present() const {
+ return _collectors_present > 0;
+}
+
+bool ThreadHeapSampler::remove_sampling_collector() {
+ assert(_collectors_present > 0, "Problem with collector counter.");
+ _collectors_present--;
+ return true;
+}
+
+bool ThreadHeapSampler::add_sampling_collector() {
+ _collectors_present++;
+ return true;
+}