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hotspot/src/share/vm/runtime/sweeper.cpp

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+/*
+ * Copyright 1997-2005 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+# include "incls/_precompiled.incl"
+# include "incls/_sweeper.cpp.incl"
+
+long      NMethodSweeper::_traversals = 0;   // No. of stack traversals performed
+CodeBlob* NMethodSweeper::_current = NULL;   // Current nmethod
+int       NMethodSweeper::_seen = 0 ;        // No. of blobs we have currently processed in current pass of CodeCache
+int       NMethodSweeper::_invocations = 0;  // No. of invocations left until we are completed with this pass
+
+jint      NMethodSweeper::_locked_seen = 0;
+jint      NMethodSweeper::_not_entrant_seen_on_stack = 0;
+bool      NMethodSweeper::_rescan = false;
+
+void NMethodSweeper::sweep() {
+  assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
+  if (!MethodFlushing) return;
+
+  // No need to synchronize access, since this is always executed at a
+  // safepoint.  If we aren't in the middle of scan and a rescan
+  // hasn't been requested then just return.
+  if (_current == NULL && !_rescan) return;
+
+  // Make sure CompiledIC_lock in unlocked, since we might update some
+  // inline caches. If it is, we just bail-out and try later.
+  if (CompiledIC_lock->is_locked() || Patching_lock->is_locked()) return;
+
+  // Check for restart
+  assert(CodeCache::find_blob_unsafe(_current) == _current, "Sweeper nmethod cached state invalid");
+  if (_current == NULL) {
+    _seen        = 0;
+    _invocations = NmethodSweepFraction;
+    _current     = CodeCache::first();
+    _traversals  += 1;
+    if (PrintMethodFlushing) {
+      tty->print_cr("### Sweep: stack traversal %d", _traversals);
+    }
+    Threads::nmethods_do();
+
+    // reset the flags since we started a scan from the beginning.
+    _rescan = false;
+    _locked_seen = 0;
+    _not_entrant_seen_on_stack = 0;
+  }
+
+  if (PrintMethodFlushing && Verbose) {
+    tty->print_cr("### Sweep at %d out of %d. Invocations left: %d", _seen, CodeCache::nof_blobs(), _invocations);
+  }
+
+  // We want to visit all nmethods after NmethodSweepFraction invocations.
+  // If invocation is 1 we do the rest
+  int todo = CodeCache::nof_blobs();
+  if (_invocations != 1) {
+    todo = (CodeCache::nof_blobs() - _seen) / _invocations;
+    _invocations--;
+  }
+
+  for(int i = 0; i < todo && _current != NULL; i++) {
+    CodeBlob* next = CodeCache::next(_current); // Read next before we potentially delete current
+    if (_current->is_nmethod()) {
+      process_nmethod((nmethod *)_current);
+    }
+    _seen++;
+    _current = next;
+  }
+  // Because we could stop on a codeBlob other than an nmethod we skip forward
+  // to the next nmethod (if any). codeBlobs other than nmethods can be freed
+  // async to us and make _current invalid while we sleep.
+  while (_current != NULL && !_current->is_nmethod()) {
+    _current = CodeCache::next(_current);
+  }
+
+  if (_current == NULL && !_rescan && (_locked_seen || _not_entrant_seen_on_stack)) {
+    // we've completed a scan without making progress but there were
+    // nmethods we were unable to process either because they were
+    // locked or were still on stack.  We don't have to aggresively
+    // clean them up so just stop scanning.  We could scan once more
+    // but that complicates the control logic and it's unlikely to
+    // matter much.
+    if (PrintMethodFlushing) {
+      tty->print_cr("### Couldn't make progress on some nmethods so stopping sweep");
+    }
+  }
+}
+
+
+void NMethodSweeper::process_nmethod(nmethod *nm) {
+  // Skip methods that are currently referenced by the VM
+  if (nm->is_locked_by_vm()) {
+    // But still remember to clean-up inline caches for alive nmethods
+    if (nm->is_alive()) {
+      // Clean-up all inline caches that points to zombie/non-reentrant methods
+      nm->cleanup_inline_caches();
+    } else {
+      _locked_seen++;
+    }
+    return;
+  }
+
+  if (nm->is_zombie()) {
+    // If it is first time, we see nmethod then we mark it. Otherwise,
+    // we reclame it. When we have seen a zombie method twice, we know that
+    // there are no inline caches that referes to it.
+    if (nm->is_marked_for_reclamation()) {
+      assert(!nm->is_locked_by_vm(), "must not flush locked nmethods");
+      nm->flush();
+    } else {
+      nm->mark_for_reclamation();
+      _rescan = true;
+    }
+  } else if (nm->is_not_entrant()) {
+    // If there is no current activations of this method on the
+    // stack we can safely convert it to a zombie method
+    if (nm->can_not_entrant_be_converted()) {
+      nm->make_zombie();
+      _rescan = true;
+    } else {
+      // Still alive, clean up its inline caches
+      nm->cleanup_inline_caches();
+      // we coudn't transition this nmethod so don't immediately
+      // request a rescan.  If this method stays on the stack for a
+      // long time we don't want to keep rescanning at every safepoint.
+      _not_entrant_seen_on_stack++;
+    }
+  } else if (nm->is_unloaded()) {
+    // Unloaded code, just make it a zombie
+    if (nm->is_osr_only_method()) {
+      // No inline caches will ever point to osr methods, so we can just remove it
+      nm->flush();
+    } else {
+      nm->make_zombie();
+      _rescan = true;
+    }
+  } else {
+    assert(nm->is_alive(), "should be alive");
+    // Clean-up all inline caches that points to zombie/non-reentrant methods
+    nm->cleanup_inline_caches();
+  }
+}