barrierSetNMethod.cpp

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#include "precompiled.hpp"
#include "code/codeCache.hpp"
#include "code/nmethod.hpp"
#include "gc/shared/barrierSet.hpp"
#include "gc/shared/barrierSetNMethod.hpp"
#include "logging/log.hpp"
#include "runtime/thread.hpp"
#include "runtime/threadWXSetters.inline.hpp"
#include "utilities/debug.hpp"

int BarrierSetNMethod::disarmed_value() const {
  return *disarmed_value_address();
}

bool BarrierSetNMethod::supports_entry_barrier(nmethod* nm) {
  if (nm->method()->is_method_handle_intrinsic()) {
    return false;
  }

  if (!nm->is_native_method() && !nm->is_compiled_by_c2() && !nm->is_compiled_by_c1()) {
    return false;
  }

  return true;
}

int BarrierSetNMethod::nmethod_stub_entry_barrier(address* return_address_ptr) {
  // Enable WXWrite: the function is called directly from nmethod_entry_barrier
  // stub.
  MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, Thread::current()));

  address return_address = *return_address_ptr;
  CodeBlob* cb = CodeCache::find_blob(return_address);
  assert(cb != NULL, "invariant");

  nmethod* nm = cb->as_nmethod();
  BarrierSetNMethod* bs_nm = BarrierSet::barrier_set()->barrier_set_nmethod();

  if (!bs_nm->is_armed(nm)) {
    return 0;
  }

  assert(!nm->is_osr_method(), "Should not reach here");
  // Called upon first entry after being armed
  bool may_enter = bs_nm->nmethod_entry_barrier(nm);

  // Diagnostic option to force deoptimization 1 in 3 times. It is otherwise
  // a very rare event.
  if (DeoptimizeNMethodBarriersALot) {
    static volatile uint32_t counter=0;
    if (Atomic::add(&counter, 1u) % 3 == 0) {
      may_enter = false;
    }
  }

  if (!may_enter) {
    log_trace(nmethod, barrier)("Deoptimizing nmethod: " PTR_FORMAT, p2i(nm));
    bs_nm->deoptimize(nm, return_address_ptr);
  }
  return may_enter ? 0 : 1;
}

bool BarrierSetNMethod::nmethod_osr_entry_barrier(nmethod* nm) {
  // This check depends on the invariant that all nmethods that are deoptimized / made not entrant
  // are NOT disarmed.
  // This invariant is important because a method can be deoptimized after the method have been
  // resolved / looked up by OSR by another thread. By not deoptimizing them we guarantee that
  // a deoptimized method will always hit the barrier and come to the same conclusion - deoptimize
  if (!is_armed(nm)) {
    return true;
  }

  assert(nm->is_osr_method(), "Should not reach here");
  log_trace(nmethod, barrier)("Running osr nmethod entry barrier: " PTR_FORMAT, p2i(nm));
  return nmethod_entry_barrier(nm);
}