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r1viollet wants to merge 12 commits into from
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Refactor thread filter mechanisms #209

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3b91530
Bench - Add a benchmark for the thread filter mechanism
r1viollet Mar 21, 2025
913d2b6
Bench - Add a benchmark for the thread filter mechanism
r1viollet Mar 21, 2025
873fcb2
thread filter - reverse lower bits
r1viollet Mar 21, 2025
be0752b
Merge branch 'r1viollet/bench_thread_filter' of github.com:DataDog/ja…
r1viollet Mar 21, 2025
0f92917
thread filter - adjust implementation
r1viollet Apr 3, 2025
258f23e
thread filter
r1viollet Apr 28, 2025
1d4efc0
thread filter - refactor recording implementation
r1viollet Apr 28, 2025
115a60a
thread filter - add a free list
r1viollet Apr 28, 2025
efa094e
Thread filter - add a table with linear probing
r1viollet Jun 25, 2025
1be1c3a
Thread filter bench - Add parameters to run different configurations …
r1viollet Jun 25, 2025
4772169
Merge branch 'main' of github.com:DataDog/java-profiler into r1violle…
r1viollet Jun 25, 2025
60ef060
Minor thread filter adjustement
r1viollet Jun 25, 2025
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39 changes: 26 additions & 13 deletions ddprof-lib/src/main/cpp/flightRecorder.cpp
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Original file line numberDiff line numberDiff line change
Expand Up@@ -318,7 +318,7 @@ char *Recording::_jvm_flags = NULL;
char *Recording::_java_command = NULL;

Recording::Recording(int fd, Arguments &args)
: _fd(fd), _thread_set(), _method_map() {
: _fd(fd), _method_map() {

args.save(_args);
_chunk_start = lseek(_fd, 0, SEEK_END);
Expand All@@ -330,6 +330,8 @@ Recording::Recording(int fd, Arguments &args)
_bytes_written = 0;

_tid = OS::threadId();
_active_index.store(0, std::memory_order_relaxed);

VM::jvmti()->GetAvailableProcessors(&_available_processors);

writeHeader(_buf);
Expand DownExpand Up@@ -1059,11 +1061,18 @@ void Recording::writeExecutionModes(Buffer *buf) {
}

void Recording::writeThreads(Buffer *buf) {
addThread(_tid);

@jbachorikjbachorikApr 29, 2025•
edited
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Is it ok to remove this call? We should make sure that the recording thread is also included as events can be associated with it - recording info, settings, config - all point to _tid thread.

@r1violletr1violletMay 6, 2025

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I think I do (with the threads.insert(_tid);)
I had to move it down a few lines.

std::vector<int> threads;
threads.reserve(_thread_set.size());
_thread_set.collect(threads);
_thread_set.clear();
int old_index = _active_index.fetch_xor(1, std::memory_order_acq_rel);
// After flip: new samples go into the new active set
// We flush from old_index (the previous active set)

std::unordered_set<int> threads;
threads.insert(_tid);

for (int i = 0; i < CONCURRENCY_LEVEL; ++i) {
// Collect thread IDs from the fixed-size table into the main set
_thread_ids[i][old_index].collect(threads);
_thread_ids[i][old_index].clear();
}

Profiler *profiler = Profiler::instance();
ThreadInfo *t_info = &profiler->_thread_info;
Expand All@@ -1072,15 +1081,15 @@ void Recording::writeThreads(Buffer *buf) {

buf->putVar64(T_THREAD);
buf->putVar64(threads.size());
for (int i = 0; i < threads.size(); i++) {
for (auto tid : threads) {
const char *thread_name;
jlong thread_id;
std::pair<std::shared_ptr<std::string>, u64> info = t_info->get(threads[i]);
std::pair<std::shared_ptr<std::string>, u64> info = t_info->get(tid);
if (info.first) {
thread_name = info.first->c_str();
thread_id = info.second;
} else {
snprintf(name_buf, sizeof(name_buf), "[tid=%d]", threads[i]);
snprintf(name_buf, sizeof(name_buf), "[tid=%d]", tid);
thread_name = name_buf;
thread_id = 0;
}
Expand All@@ -1090,9 +1099,9 @@ void Recording::writeThreads(Buffer *buf) {
(thread_id == 0 ? length + 1 : 2 * length) -
3 * 10; // 3x max varint length
flushIfNeeded(buf, required);
buf->putVar64(threads[i]);
buf->putVar64(tid);
buf->putUtf8(thread_name, length);
buf->putVar64(threads[i]);
buf->putVar64(tid);
if (thread_id == 0) {
buf->put8(0);
} else {
Expand DownExpand Up@@ -1442,7 +1451,11 @@ void Recording::recordCpuLoad(Buffer *buf, float proc_user, float proc_system,
flushIfNeeded(buf);
}

void Recording::addThread(int tid) { _thread_set.add(tid); }
// assumption is that we hold the lock (with lock_index)
void Recording::addThread(int lock_index, int tid) {
int active = _active_index.load(std::memory_order_acquire);
_thread_ids[lock_index][active].insert(tid);

@jbachorikjbachorikApr 29, 2025

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I wonder - does the ordering matter here?
Eg. if we have [active][lock_index] can it make things better/worse in terms of data locality?

@r1violletr1violletJun 13, 2025

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this is not acceptable: no allocations can take place here.

}

Error FlightRecorder::start(Arguments &args, bool reset) {
const char *file = args.file();
Expand DownExpand Up@@ -1599,7 +1612,7 @@ void FlightRecorder::recordEvent(int lock_index, int tid, u32 call_trace_id,
break;
}
_rec->flushIfNeeded(buf);
_rec->addThread(tid);
_rec->addThread(lock_index, tid);
}
}

Expand Down
13 changes: 10 additions & 3 deletions ddprof-lib/src/main/cpp/flightRecorder.h
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Original file line numberDiff line numberDiff line change
Expand Up@@ -18,6 +18,7 @@
#define _FLIGHTRECORDER_H

#include <map>
#include <unordered_set>

#include <limits.h>
#include <string.h>
Expand All@@ -34,6 +35,7 @@
#include "mutex.h"
#include "objectSampler.h"
#include "threadFilter.h"
#include "threadIdTable.h"
#include "vmEntry.h"

const u64 MAX_JLONG = 0x7fffffffffffffffULL;
Expand DownExpand Up@@ -127,9 +129,13 @@ class Recording {
static char *_java_command;

RecordingBuffer _buf[CONCURRENCY_LEVEL];
// we have several tables to avoid lock contention
// we have a second dimension to allow a switch in the active table
ThreadIdTable _thread_ids[CONCURRENCY_LEVEL][2];
std::atomic<int> _active_index{0}; // 0 or 1 globally

int _fd;
off_t _chunk_start;
ThreadFilter _thread_set;
MethodMap _method_map;

Arguments _args;
Expand DownExpand Up@@ -158,7 +164,7 @@ class Recording {
public:
Recording(int fd, Arguments &args);
~Recording();

void copyTo(int target_fd);
off_t finishChunk();

Expand DownExpand Up@@ -258,7 +264,8 @@ class Recording {
LockEvent *event);
void recordCpuLoad(Buffer *buf, float proc_user, float proc_system,
float machine_total);
void addThread(int tid);

void addThread(int lock_index, int tid);
};

class Lookup {
Expand Down
69 changes: 44 additions & 25 deletions ddprof-lib/src/main/cpp/javaApi.cpp
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Original file line numberDiff line numberDiff line change
Expand Up@@ -123,19 +123,59 @@ Java_com_datadoghq_profiler_JavaProfiler_getSamples(JNIEnv *env,
return (jlong)Profiler::instance()->total_samples();
}

// some duplication between add and remove, though we want to avoid having an extra branch in the hot path
extern "C" DLLEXPORT void JNICALL
Java_com_datadoghq_profiler_JavaProfiler_filterThreadAdd0(JNIEnv *env,
jobject unused) {
ProfiledThread *current = ProfiledThread::current();
int tid = current->tid();
if (unlikely(tid < 0)) {
return;
}
ThreadFilter *thread_filter = Profiler::instance()->threadFilter();
int slot_id = current->filterSlotId();
if (unlikely(slot_id == -1)) {
return;
}
thread_filter->add(tid, slot_id);
}

extern "C" DLLEXPORT void JNICALL
Java_com_datadoghq_profiler_JavaProfiler_filterThreadRemove0(JNIEnv *env,
jobject unused) {
ProfiledThread *current = ProfiledThread::current();
int tid = current->tid();
if (unlikely(tid < 0)) {
return;
}
ThreadFilter *thread_filter = Profiler::instance()->threadFilter();
int slot_id = current->filterSlotId();
if (unlikely(slot_id == -1)) {
return;
}
thread_filter->remove(slot_id);
}

// Backward compatibility for existing code
extern "C" DLLEXPORT void JNICALL
Java_com_datadoghq_profiler_JavaProfiler_filterThread0(JNIEnv *env,
jobject unused,
jboolean enable) {
int tid = ProfiledThread::currentTid();
if (tid < 0) {
ProfiledThread *current = ProfiledThread::current();
int tid = current->tid();
if (unlikely(tid < 0)) {
return;
}
ThreadFilter *thread_filter = Profiler::instance()->threadFilter();
int slot_id = current->filterSlotId();
if (unlikely(slot_id == -1)) {
return;
}

if (enable) {
thread_filter->add(tid);
thread_filter->add(tid, slot_id);
} else {
thread_filter->remove(tid);
thread_filter->remove(slot_id);
}
}

Expand DownExpand Up@@ -406,24 +446,3 @@ Java_com_datadoghq_profiler_JVMAccess_healthCheck0(JNIEnv *env,
jobject unused) {
return true;
}

extern "C" DLLEXPORT jlong JNICALL
Java_com_datadoghq_profiler_ActiveBitmap_bitmapAddressFor0(JNIEnv *env,
jclass unused,
jint tid) {
u64* bitmap = Profiler::instance()->threadFilter()->bitmapAddressFor((int)tid);
return (jlong)bitmap;
}

extern "C" DLLEXPORT jboolean JNICALL
Java_com_datadoghq_profiler_ActiveBitmap_isActive0(JNIEnv *env,
jclass unused,
jint tid) {
return Profiler::instance()->threadFilter()->accept((int)tid) ? JNI_TRUE : JNI_FALSE;
}

extern "C" DLLEXPORT jlong JNICALL
Java_com_datadoghq_profiler_ActiveBitmap_getActiveCountAddr0(JNIEnv *env,
jclass unused) {
return (jlong)Profiler::instance()->threadFilter()->addressOfSize();
}
15 changes: 10 additions & 5 deletions ddprof-lib/src/main/cpp/profiler.cpp
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Original file line numberDiff line numberDiff line change
Expand Up@@ -104,10 +104,12 @@ void Profiler::addRuntimeStub(const void *address, int length,

void Profiler::onThreadStart(jvmtiEnv *jvmti, JNIEnv *jni, jthread thread) {
ProfiledThread::initCurrentThread();

int tid = ProfiledThread::currentTid();
ProfiledThread *current = ProfiledThread::current();
int tid = current->tid();
if (_thread_filter.enabled()) {
_thread_filter.remove(tid);
int slot_id = _thread_filter.registerThread();
current->setFilterSlotId(slot_id);
_thread_filter.remove(slot_id); // Remove from filtering initially
}
updateThreadName(jvmti, jni, thread, true);

Expand All@@ -116,9 +118,12 @@ void Profiler::onThreadStart(jvmtiEnv *jvmti, JNIEnv *jni, jthread thread) {
}

void Profiler::onThreadEnd(jvmtiEnv *jvmti, JNIEnv *jni, jthread thread) {
int tid = ProfiledThread::currentTid();
ProfiledThread *current = ProfiledThread::current();
int slot_id = current->filterSlotId();
int tid = current->tid();
if (_thread_filter.enabled()) {
_thread_filter.remove(tid);
_thread_filter.unregisterThread(slot_id);
current->setFilterSlotId(-1);
}
updateThreadName(jvmti, jni, thread, true);

Expand Down
6 changes: 5 additions & 1 deletion ddprof-lib/src/main/cpp/thread.h
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Original file line numberDiff line numberDiff line change
Expand Up@@ -43,11 +43,12 @@ class ProfiledThread : public ThreadLocalData {
u32 _wall_epoch;
u32 _call_trace_id;
u32 _recording_epoch;
int _filter_slot_id; // Slot ID for thread filtering
UnwindFailures _unwind_failures;

ProfiledThread(int buffer_pos, int tid)
: ThreadLocalData(), _pc(0), _span_id(0), _crash_depth(0), _buffer_pos(buffer_pos), _tid(tid), _cpu_epoch(0),
_wall_epoch(0), _call_trace_id(0), _recording_epoch(0) {};
_wall_epoch(0), _call_trace_id(0), _recording_epoch(0), _filter_slot_id(-1) {};

void releaseFromBuffer();

Expand DownExpand Up@@ -120,6 +121,9 @@ class ProfiledThread : public ThreadLocalData {
}

static void signalHandler(int signo, siginfo_t *siginfo, void *ucontext);

int filterSlotId() { return _filter_slot_id; }
void setFilterSlotId(int slotId) { _filter_slot_id = slotId; }
};

#endif // _THREAD_H
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