--- a/src/hotspot/share/runtime/safepoint.hpp Fri Feb 15 07:53:03 2019 -0500
+++ b/src/hotspot/share/runtime/safepoint.hpp Fri Feb 15 14:15:10 2019 +0100
@@ -26,15 +26,15 @@
#define SHARE_RUNTIME_SAFEPOINT_HPP
#include "memory/allocation.hpp"
-#include "runtime/mutexLocker.hpp"
#include "runtime/os.hpp"
-#include "utilities/globalDefinitions.hpp"
+#include "runtime/thread.hpp"
#include "utilities/ostream.hpp"
+#include "utilities/waitBarrier.hpp"
//
// Safepoint synchronization
////
-// The VMThread or CMS_thread uses the SafepointSynchronize::begin/end
+// The VMThread uses the SafepointSynchronize::begin/end
// methods to enter/exit a safepoint region. The begin method will roll
// all JavaThreads forward to a safepoint.
//
@@ -45,9 +45,7 @@
// exit safepoint methods, when a thread is blocked/restarted. Hence, all mutex exter/
// exit points *must* be at a safepoint.
-
class ThreadSafepointState;
-class JavaThread;
//
// Implements roll-forward to safepoint (safepoint synchronization)
@@ -55,21 +53,10 @@
class SafepointSynchronize : AllStatic {
public:
enum SynchronizeState {
- _not_synchronized = 0, // Threads not synchronized at a safepoint
- // Keep this value 0. See the comment in do_call_back()
+ _not_synchronized = 0, // Threads not synchronized at a safepoint. Keep this value 0.
_synchronizing = 1, // Synchronizing in progress
- _synchronized = 2 // All Java threads are stopped at a safepoint. Only VM thread is running
- };
-
- enum SafepointingThread {
- _null_thread = 0,
- _vm_thread = 1,
- _other_thread = 2
- };
-
- enum SafepointTimeoutReason {
- _spinning_timeout = 0,
- _blocking_timeout = 1
+ _synchronized = 2 // All Java threads are running in native, blocked in OS or stopped at safepoint.
+ // VM thread and any NonJavaThread may be running.
};
// The enums are listed in the order of the tasks when done serially.
@@ -86,22 +73,33 @@
};
private:
- static volatile SynchronizeState _state; // Threads might read this flag directly, without acquiring the Threads_lock
- static volatile int _waiting_to_block; // number of threads we are waiting for to block
- static int _current_jni_active_count; // Counts the number of active critical natives during the safepoint
- static int _defer_thr_suspend_loop_count; // Iterations before blocking VM threads
+ friend class SafepointMechanism;
+ friend class ThreadSafepointState;
+ friend class HandshakeState;
+
+ enum SafepointTimeoutReason {
+ _spinning_timeout = 0,
+ _blocking_timeout = 1
+ };
+
+ // Threads might read this flag directly, without acquiring the Threads_lock:
+ static volatile SynchronizeState _state;
+ // Number of threads we are waiting for to block:
+ static int _waiting_to_block;
+ // Counts the number of active critical natives during the safepoint:
+ static int _current_jni_active_count;
// This counter is used for fast versions of jni_Get<Primitive>Field.
- // An even value means there is no ongoing safepoint operations.
+ // An even value means there are no ongoing safepoint operations.
// The counter is incremented ONLY at the beginning and end of each
- // safepoint. The fact that Threads_lock is held throughout each pair of
- // increments (at the beginning and end of each safepoint) guarantees
- // race freedom.
+ // safepoint.
static volatile uint64_t _safepoint_counter;
-private:
- static long _end_of_last_safepoint; // Time of last safepoint in milliseconds
- static julong _coalesced_vmop_count; // coalesced vmop count
+ // JavaThreads that need to block for the safepoint will stop on the
+ // _wait_barrier, where they can quickly be started again.
+ static WaitBarrier* _wait_barrier;
+ static long _end_of_last_safepoint; // Time of last safepoint in milliseconds
+ static julong _coalesced_vmop_count; // coalesced vmop count
// Statistics
static void begin_statistics(int nof_threads, int nof_running);
@@ -114,42 +112,41 @@
// For debug long safepoint
static void print_safepoint_timeout(SafepointTimeoutReason timeout_reason);
+ // Helper methods for safepoint procedure:
+ static void arm_safepoint();
+ static int synchronize_threads(jlong safepoint_limit_time, int nof_threads, int* initial_running);
+ static void disarm_safepoint();
+ static void increment_jni_active_count();
+ static void decrement_waiting_to_block();
+
+ // Used in safepoint_safe to do a stable load of the thread state.
+ static bool try_stable_load_state(JavaThreadState *state,
+ JavaThread *thread,
+ uint64_t safepoint_count);
+
+ // Called when a thread voluntarily blocks
+ static void block(JavaThread *thread);
+
+ // Called from VMThread during handshakes.
+ // If true the VMThread may safely process the handshake operation for the JavaThread.
+ static bool handshake_safe(JavaThread *thread);
+
public:
- // Main entry points
+ static void init(Thread* vmthread);
- // Roll all threads forward to safepoint. Must be called by the
- // VMThread or CMS_thread.
+ // Roll all threads forward to safepoint. Must be called by the VMThread.
static void begin();
static void end(); // Start all suspended threads again...
- static bool safepoint_safe(JavaThread *thread, JavaThreadState state);
-
- static void check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state);
+ // The value for a not set safepoint id.
+ static const uint64_t InactiveSafepointCounter;
// Query
- inline static bool is_at_safepoint() { return _state == _synchronized; }
- inline static bool is_synchronizing() { return _state == _synchronizing; }
- inline static uint64_t safepoint_counter() { return _safepoint_counter; }
-
- inline static void increment_jni_active_count() {
- assert_locked_or_safepoint(Safepoint_lock);
- _current_jni_active_count++;
- }
-
-private:
- inline static bool do_call_back() {
- return (_state != _not_synchronized);
- }
-
- // Called when a thread voluntarily blocks
- static void block(JavaThread *thread, bool block_in_safepoint_check = true);
-
- friend class SafepointMechanism;
-
-public:
- static void signal_thread_at_safepoint() { _waiting_to_block--; }
-
+ static bool is_at_safepoint() { return _state == _synchronized; }
+ static bool is_synchronizing() { return _state == _synchronizing; }
+ static uint64_t safepoint_counter() { return _safepoint_counter; }
+ static bool is_same_safepoint(uint64_t counter) { return (SafepointSynchronize::safepoint_counter() - counter) < 2; }
// Exception handling for page polling
static void handle_polling_page_exception(JavaThread *thread);
@@ -164,13 +161,13 @@
static void do_cleanup_tasks();
static void print_stat_on_exit();
- inline static void inc_vmop_coalesced_count() { _coalesced_vmop_count++; }
+ static void inc_vmop_coalesced_count() { _coalesced_vmop_count++; }
- static void set_is_at_safepoint() { _state = _synchronized; }
- static void set_is_not_at_safepoint() { _state = _not_synchronized; }
+ static void set_is_at_safepoint() { _state = _synchronized; }
+ static void set_is_not_at_safepoint() { _state = _not_synchronized; }
// Assembly support
- static address address_of_state() { return (address)&_state; }
+ static address address_of_state() { return (address)&_state; }
// Only used for making sure that no safepoint has happened in
// JNI_FastGetField. Therefore only the low 32-bits are needed
@@ -201,44 +198,43 @@
// State class for a thread suspended at a safepoint
class ThreadSafepointState: public CHeapObj<mtInternal> {
- public:
- // These states are maintained by VM thread while threads are being brought
- // to a safepoint. After SafepointSynchronize::end(), they are reset to
- // _running.
- enum suspend_type {
- _running = 0, // Thread state not yet determined (i.e., not at a safepoint yet)
- _at_safepoint = 1, // Thread at a safepoint (f.ex., when blocked on a lock)
- _call_back = 2 // Keep executing and wait for callback (if thread is in interpreted or vm)
- };
private:
- volatile bool _at_poll_safepoint; // At polling page safepoint (NOT a poll return safepoint)
- // Thread has called back the safepoint code (for debugging)
- bool _has_called_back;
+ // At polling page safepoint (NOT a poll return safepoint):
+ volatile bool _at_poll_safepoint;
+ JavaThread* _thread;
+ bool _safepoint_safe;
+ volatile uint64_t _safepoint_id;
+ JavaThreadState _orig_thread_state;
- JavaThread * _thread;
- volatile suspend_type _type;
- JavaThreadState _orig_thread_state;
+ ThreadSafepointState* _next;
+ void account_safe_thread();
public:
ThreadSafepointState(JavaThread *thread);
- // examine/roll-forward/restart
- void examine_state_of_thread();
- void roll_forward(suspend_type type);
+ // Linked list support:
+ ThreadSafepointState* get_next() const { return _next; }
+ void set_next(ThreadSafepointState* value) { _next = value; }
+ ThreadSafepointState** next_ptr() { return &_next; }
+
+ // examine/restart
+ void examine_state_of_thread(uint64_t safepoint_count);
void restart();
// Query
JavaThread* thread() const { return _thread; }
- suspend_type type() const { return _type; }
- bool is_running() const { return (_type==_running); }
+ bool is_running() const { return !_safepoint_safe; }
+
+ uint64_t get_safepoint_id() const;
+ void reset_safepoint_id();
+ void set_safepoint_id(uint64_t sid);
+
JavaThreadState orig_thread_state() const { return _orig_thread_state; }
// Support for safepoint timeout (debugging)
- bool has_called_back() const { return _has_called_back; }
- void set_has_called_back(bool val) { _has_called_back = val; }
- bool is_at_poll_safepoint() { return _at_poll_safepoint; }
- void set_at_poll_safepoint(bool val) { _at_poll_safepoint = val; }
+ bool is_at_poll_safepoint() { return _at_poll_safepoint; }
+ void set_at_poll_safepoint(bool val) { _at_poll_safepoint = val; }
void handle_polling_page_exception();