/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* 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
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*/
#ifndef SHARE_VM_MEMORY_GCLOCKER_HPP
#define SHARE_VM_MEMORY_GCLOCKER_HPP
#include "gc_interface/collectedHeap.hpp"
#include "memory/genCollectedHeap.hpp"
#include "memory/universe.hpp"
#ifdef TARGET_OS_FAMILY_linux
# include "os_linux.inline.hpp"
# include "thread_linux.inline.hpp"
#endif
#ifdef TARGET_OS_FAMILY_solaris
# include "os_solaris.inline.hpp"
# include "thread_solaris.inline.hpp"
#endif
#ifdef TARGET_OS_FAMILY_windows
# include "os_windows.inline.hpp"
# include "thread_windows.inline.hpp"
#endif
#ifdef TARGET_OS_FAMILY_bsd
# include "os_bsd.inline.hpp"
# include "thread_bsd.inline.hpp"
#endif
// decrements the count to zero. Avoid calling these if at all possible.
private:
// The _jni_lock_count keeps track of the number of threads that are
// currently in a critical region. It's only kept up to date when
// _needs_gc is true. The current value is computed during
// safepointing and decremented during the slow path of GC_locker
// unlocking.
// note: bool is typedef'd as jint
#ifdef ASSERT
// This lock count is updated for all operations and is used to
// validate the jni_lock_count that is computed during safepoints.
#endif
// Accessors
static bool is_jni_active() {
return _jni_lock_count > 0;
}
// At a safepoint, visit all threads and count the number of active
// critical sections. This is used to ensure that all active
// critical sections are exited before a new one is started.
static bool is_active_internal() {
return _lock_count > 0 || _jni_lock_count > 0;
}
public:
// Accessors
static bool is_active() {
return is_active_internal();
}
// Shorthand
static bool is_active_and_needs_gc() {
// Use is_active_internal since _needs_gc can change from true to
// false outside of a safepoint, triggering the assert in
// is_active.
return needs_gc() && is_active_internal();
}
// In debug mode track the locking state at all times
static void increment_debug_jni_lock_count() {
#ifdef ASSERT
#endif
}
static void decrement_debug_jni_lock_count() {
#ifdef ASSERT
#endif
}
// Set the current lock count
}
// Sets _needs_gc if is_active() is true. Returns is_active().
static bool check_active_before_gc();
// Stalls the caller (who should not be in a jni critical section)
// until needs_gc() clears. Note however that needs_gc() may be
// JNICritical_lock, so the caller may not safely assert upon
// return from this method that "!needs_gc()" since that is
// not a stable predicate.
static void stall_until_clear();
// Non-structured GC locking: currently needed for JNI. Use with care!
static void lock();
static void unlock();
// The following two methods are used for JNI critical regions.
// If we find that we failed to perform a GC because the GC_locker
// was active, arrange for one as soon as possible by allowing
// all threads in critical regions to complete, but not allowing
// other critical regions to be entered. The reasons for that are:
// 1) a GC request won't be starved by overlapping JNI critical
// region activities, which can cause unnecessary OutOfMemory errors.
// 2) even if allocation requests can still be satisfied before GC locker
// becomes inactive, for example, in tenured generation possibly with
// heap expansion, those allocations can trigger lots of safepointing
// attempts (ineffective GC attempts) and require Heap_lock which
// slow down allocations tremendously.
//
// Note that critical regions can be nested in a single thread, so
// we must allow threads already in critical regions to continue.
//
// JNI critical regions are the only participants in this scheme
// because they are, by spec, well bounded while in a critical region.
//
// Each of the following two method is split into a fast path and a
// slow path. JNICritical_lock is only grabbed in the slow path.
// _needs_gc is initially false and every java thread will go
// through the fast path, which simply increments or decrements the
// current thread's critical count. When GC happens at a safepoint,
// GC_locker::is_active() is checked. Since there is no safepoint in
// the fast path of lock_critical() and unlock_critical(), there is
// no race condition between the fast path and GC. After _needs_gc
// is set at a safepoint, every thread will go through the slow path
// after the safepoint. Since after a safepoint, each of the
// following two methods is either entered from the method entry and
// falls into the slow path, or is resumed from the safepoints in
// the method, which only exist in the slow path. So when _needs_gc
// is set, the slow path is always taken, till _needs_gc is cleared.
};
// A No_GC_Verifier object can be placed in methods where one assumes that
// no garbage collection will occur. The destructor will verify this property
// unless the constructor is called with argument false (not verifygc).
//
// The check will only be done in debug mode and if verifygc true.
friend class Pause_No_GC_Verifier;
protected:
bool _verifygc;
unsigned int _old_invocations;
public:
#ifdef ASSERT
No_GC_Verifier(bool verifygc = true);
~No_GC_Verifier();
#else
~No_GC_Verifier() {}
#endif
};
// A Pause_No_GC_Verifier is used to temporarily pause the behavior
// of a No_GC_Verifier object. If we are not in debug mode or if the
// No_GC_Verifier object has a _verifygc value of false, then there
// is nothing to do.
private:
public:
#ifdef ASSERT
#else
~Pause_No_GC_Verifier() {}
#endif
};
// A No_Safepoint_Verifier object will throw an assertion failure if
// the current thread passes a possible safepoint while this object is
// instantiated. A safepoint, will either be: an oop allocation, blocking
// on a Mutex or JavaLock, or executing a VM operation.
//
// If StrictSafepointChecks is turned off, it degrades into a No_GC_Verifier
//
friend class Pause_No_Safepoint_Verifier;
private:
bool _activated;
public:
#ifdef ASSERT
if (_activated) {
}
}
if (_activated) {
}
}
#else
~No_Safepoint_Verifier() {}
#endif
};
// A Pause_No_Safepoint_Verifier is used to temporarily pause the
// behavior of a No_Safepoint_Verifier object. If we are not in debug
// mode then there is nothing to do. If the No_Safepoint_Verifier
// object has an _activated value of false, then there is nothing to
// do for safepoint and allocation checking, but there may still be
// something to do for the underlying No_GC_Verifier object.
private:
public:
#ifdef ASSERT
: Pause_No_GC_Verifier(nsv) {
if (_nsv->_activated) {
}
}
if (_nsv->_activated) {
}
}
#else
: Pause_No_GC_Verifier(nsv) {}
#endif
};
// A SkipGCALot object is used to elide the usual effect of gc-a-lot
// over a section of execution by a thread. Currently, it's used only to
// prevent re-entrant calls to GC.
private:
bool _saved;
public:
#ifdef ASSERT
_t->set_skip_gcalot(true);
}
~SkipGCALot() {
}
#else
~SkipGCALot() { }
#endif
};
// JRT_LEAF currently can be called from either _thread_in_Java or
// _thread_in_native mode. In _thread_in_native, it is ok
// for another thread to trigger GC. The rest of the JRT_LEAF
// rules apply.
static bool should_verify_GC();
public:
#ifdef ASSERT
#else
JRT_Leaf_Verifier() {}
~JRT_Leaf_Verifier() {}
#endif
};
// A No_Alloc_Verifier object can be placed in methods where one assumes that
// no allocation will occur. The destructor will verify this property
// unless the constructor is called with argument false (not activated).
//
// The check will only be done in debug mode and if activated.
// Note: this only makes sense at safepoints (otherwise, other threads may
// allocate concurrently.)
private:
bool _activated;
public:
#ifdef ASSERT
}
~No_Alloc_Verifier() {
}
#else
~No_Alloc_Verifier() {}
#endif
};
#endif // SHARE_VM_MEMORY_GCLOCKER_HPP