1 /*
   2  * Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #ifndef SHARE_VM_MEMORY_ALLOCATION_HPP
  26 #define SHARE_VM_MEMORY_ALLOCATION_HPP
  27 
  28 #include "runtime/globals.hpp"
  29 #include "utilities/globalDefinitions.hpp"
  30 #include "utilities/macros.hpp"
  31 
  32 #include <new>
  33 
  34 class AllocFailStrategy {
  35 public:
  36   enum AllocFailEnum { EXIT_OOM, RETURN_NULL };
  37 };
  38 typedef AllocFailStrategy::AllocFailEnum AllocFailType;
  39 
  40 // The virtual machine must never call one of the implicitly declared
  41 // global allocation or deletion functions.  (Such calls may result in
  42 // link-time or run-time errors.)  For convenience and documentation of
  43 // intended use, classes in the virtual machine may be derived from one
  44 // of the following allocation classes, some of which define allocation
  45 // and deletion functions.
  46 // Note: std::malloc and std::free should never called directly.
  47 
  48 //
  49 // For objects allocated in the resource area (see resourceArea.hpp).
  50 // - ResourceObj
  51 //
  52 // For objects allocated in the C-heap (managed by: free & malloc and tracked with NMT)
  53 // - CHeapObj
  54 //
  55 // For objects allocated on the stack.
  56 // - StackObj
  57 //
  58 // For classes used as name spaces.
  59 // - AllStatic
  60 //
  61 // For classes in Metaspace (class data)
  62 // - MetaspaceObj
  63 //
  64 // The printable subclasses are used for debugging and define virtual
  65 // member functions for printing. Classes that avoid allocating the
  66 // vtbl entries in the objects should therefore not be the printable
  67 // subclasses.
  68 //
  69 // The following macros and function should be used to allocate memory
  70 // directly in the resource area or in the C-heap, The _OBJ variants
  71 // of the NEW/FREE_C_HEAP macros are used for alloc/dealloc simple
  72 // objects which are not inherited from CHeapObj, note constructor and
  73 // destructor are not called. The preferable way to allocate objects
  74 // is using the new operator.
  75 //
  76 // WARNING: The array variant must only be used for a homogenous array
  77 // where all objects are of the exact type specified. If subtypes are
  78 // stored in the array then must pay attention to calling destructors
  79 // at needed.
  80 //
  81 //   NEW_RESOURCE_ARRAY(type, size)
  82 //   NEW_RESOURCE_OBJ(type)
  83 //   NEW_C_HEAP_ARRAY(type, size)
  84 //   NEW_C_HEAP_OBJ(type, memflags)
  85 //   FREE_C_HEAP_ARRAY(type, old)
  86 //   FREE_C_HEAP_OBJ(objname, type, memflags)
  87 //   char* AllocateHeap(size_t size, const char* name);
  88 //   void  FreeHeap(void* p);
  89 //
  90 
  91 // In non product mode we introduce a super class for all allocation classes
  92 // that supports printing.
  93 // We avoid the superclass in product mode to save space.
  94 
  95 #ifdef PRODUCT
  96 #define ALLOCATION_SUPER_CLASS_SPEC
  97 #else
  98 #define ALLOCATION_SUPER_CLASS_SPEC : public AllocatedObj
  99 class AllocatedObj {
 100  public:
 101   // Printing support
 102   void print() const;
 103   void print_value() const;
 104 
 105   virtual void print_on(outputStream* st) const;
 106   virtual void print_value_on(outputStream* st) const;
 107 };
 108 #endif
 109 
 110 
 111 /*
 112  * Memory types
 113  */
 114 enum MemoryType {
 115   // Memory type by sub systems. It occupies lower byte.
 116   mtJavaHeap          = 0x00,  // Java heap
 117   mtClass             = 0x01,  // memory class for Java classes
 118   mtThread            = 0x02,  // memory for thread objects
 119   mtThreadStack       = 0x03,
 120   mtCode              = 0x04,  // memory for generated code
 121   mtGC                = 0x05,  // memory for GC
 122   mtCompiler          = 0x06,  // memory for compiler
 123   mtInternal          = 0x07,  // memory used by VM, but does not belong to
 124                                  // any of above categories, and not used for
 125                                  // native memory tracking
 126   mtOther             = 0x08,  // memory not used by VM
 127   mtSymbol            = 0x09,  // symbol
 128   mtNMT               = 0x0A,  // memory used by native memory tracking
 129   mtClassShared       = 0x0B,  // class data sharing
 130   mtChunk             = 0x0C,  // chunk that holds content of arenas
 131   mtTest              = 0x0D,  // Test type for verifying NMT
 132   mtTracing           = 0x0E,  // memory used for Tracing
 133   mtLogging           = 0x0F,  // memory for logging
 134   mtArguments         = 0x10,  // memory for argument processing
 135   mtModule            = 0x11,  // memory for module processing
 136   mtNone              = 0x12,  // undefined
 137   mt_number_of_types  = 0x13   // number of memory types (mtDontTrack
 138                                  // is not included as validate type)
 139 };
 140 
 141 typedef MemoryType MEMFLAGS;
 142 
 143 
 144 #if INCLUDE_NMT
 145 
 146 extern bool NMT_track_callsite;
 147 
 148 #else
 149 
 150 const bool NMT_track_callsite = false;
 151 
 152 #endif // INCLUDE_NMT
 153 
 154 class NativeCallStack;
 155 
 156 
 157 char* AllocateHeap(size_t size,
 158                    MEMFLAGS flags,
 159                    const NativeCallStack& stack,
 160                    AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
 161 char* AllocateHeap(size_t size,
 162                    MEMFLAGS flags,
 163                    AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
 164 
 165 char* ReallocateHeap(char *old,
 166                      size_t size,
 167                      MEMFLAGS flag,
 168                      AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
 169 
 170 void FreeHeap(void* p);
 171 
 172 template <MEMFLAGS F> class CHeapObj ALLOCATION_SUPER_CLASS_SPEC {
 173  public:
 174   ALWAYSINLINE void* operator new(size_t size) throw() {
 175     return (void*)AllocateHeap(size, F);
 176   }
 177 
 178   ALWAYSINLINE void* operator new(size_t size,
 179                                   const NativeCallStack& stack) throw() {
 180     return (void*)AllocateHeap(size, F, stack);
 181   }
 182 
 183   ALWAYSINLINE void* operator new(size_t size, const std::nothrow_t&,
 184                                   const NativeCallStack& stack) throw() {
 185     return (void*)AllocateHeap(size, F, stack, AllocFailStrategy::RETURN_NULL);
 186   }
 187 
 188   ALWAYSINLINE void* operator new(size_t size, const std::nothrow_t&) throw() {
 189     return (void*)AllocateHeap(size, F, AllocFailStrategy::RETURN_NULL);
 190   }
 191 
 192   ALWAYSINLINE void* operator new[](size_t size) throw() {
 193     return (void*)AllocateHeap(size, F);
 194   }
 195 
 196   ALWAYSINLINE void* operator new[](size_t size,
 197                                   const NativeCallStack& stack) throw() {
 198     return (void*)AllocateHeap(size, F, stack);
 199   }
 200 
 201   ALWAYSINLINE void* operator new[](size_t size, const std::nothrow_t&,
 202                                     const NativeCallStack& stack) throw() {
 203     return (void*)AllocateHeap(size, F, stack, AllocFailStrategy::RETURN_NULL);
 204   }
 205 
 206   ALWAYSINLINE void* operator new[](size_t size, const std::nothrow_t&) throw() {
 207     return (void*)AllocateHeap(size, F, AllocFailStrategy::RETURN_NULL);
 208   }
 209 
 210   void  operator delete(void* p)     { FreeHeap(p); }
 211   void  operator delete [] (void* p) { FreeHeap(p); }
 212 };
 213 
 214 // Base class for objects allocated on the stack only.
 215 // Calling new or delete will result in fatal error.
 216 
 217 class StackObj ALLOCATION_SUPER_CLASS_SPEC {
 218  private:
 219   void* operator new(size_t size) throw();
 220   void* operator new [](size_t size) throw();
 221 #ifdef __IBMCPP__
 222  public:
 223 #endif
 224   void  operator delete(void* p);
 225   void  operator delete [](void* p);
 226 };
 227 
 228 // Base class for objects stored in Metaspace.
 229 // Calling delete will result in fatal error.
 230 //
 231 // Do not inherit from something with a vptr because this class does
 232 // not introduce one.  This class is used to allocate both shared read-only
 233 // and shared read-write classes.
 234 //
 235 
 236 class ClassLoaderData;
 237 class MetaspaceClosure;
 238 
 239 class MetaspaceObj {
 240   friend class MetaspaceShared;
 241   // When CDS is enabled, all shared metaspace objects are mapped
 242   // into a single contiguous memory block, so we can use these
 243   // two pointers to quickly determine if something is in the
 244   // shared metaspace.
 245   //
 246   // When CDS is not enabled, both pointers are set to NULL.
 247   static void* _shared_metaspace_base; // (inclusive) low address
 248   static void* _shared_metaspace_top;  // (exclusive) high address
 249 
 250  public:
 251   bool is_metaspace_object() const;
 252   bool is_shared() const {
 253     // If no shared metaspace regions are mapped, _shared_metaspace_{base,top} will
 254     // both be NULL and all values of p will be rejected quickly.
 255     return (((void*)this) < _shared_metaspace_top && ((void*)this) >= _shared_metaspace_base);
 256   }
 257   void print_address_on(outputStream* st) const;  // nonvirtual address printing
 258 
 259 #define METASPACE_OBJ_TYPES_DO(f) \
 260   f(Class) \
 261   f(Symbol) \
 262   f(TypeArrayU1) \
 263   f(TypeArrayU2) \
 264   f(TypeArrayU4) \
 265   f(TypeArrayU8) \
 266   f(TypeArrayOther) \
 267   f(Method) \
 268   f(ConstMethod) \
 269   f(MethodData) \
 270   f(ConstantPool) \
 271   f(ConstantPoolCache) \
 272   f(Annotations) \
 273   f(MethodCounters)
 274 
 275 #define METASPACE_OBJ_TYPE_DECLARE(name) name ## Type,
 276 #define METASPACE_OBJ_TYPE_NAME_CASE(name) case name ## Type: return #name;
 277 
 278   enum Type {
 279     // Types are MetaspaceObj::ClassType, MetaspaceObj::SymbolType, etc
 280     METASPACE_OBJ_TYPES_DO(METASPACE_OBJ_TYPE_DECLARE)
 281     _number_of_types
 282   };
 283 
 284   static const char * type_name(Type type) {
 285     switch(type) {
 286     METASPACE_OBJ_TYPES_DO(METASPACE_OBJ_TYPE_NAME_CASE)
 287     default:
 288       ShouldNotReachHere();
 289       return NULL;
 290     }
 291   }
 292 
 293   static MetaspaceObj::Type array_type(size_t elem_size) {
 294     switch (elem_size) {
 295     case 1: return TypeArrayU1Type;
 296     case 2: return TypeArrayU2Type;
 297     case 4: return TypeArrayU4Type;
 298     case 8: return TypeArrayU8Type;
 299     default:
 300       return TypeArrayOtherType;
 301     }
 302   }
 303 
 304   void* operator new(size_t size, ClassLoaderData* loader_data,
 305                      size_t word_size,
 306                      Type type, Thread* thread) throw();
 307                      // can't use TRAPS from this header file.
 308   void operator delete(void* p) { ShouldNotCallThis(); }
 309 
 310   // Declare a *static* method with the same signature in any subclass of MetaspaceObj
 311   // that should be read-only by default. See symbol.hpp for an example. This function
 312   // is used by the templates in metaspaceClosure.hpp
 313   static bool is_read_only_by_default() { return false; }
 314 };
 315 
 316 // Base class for classes that constitute name spaces.
 317 
 318 class Arena;
 319 
 320 class AllStatic {
 321  public:
 322   AllStatic()  { ShouldNotCallThis(); }
 323   ~AllStatic() { ShouldNotCallThis(); }
 324 };
 325 
 326 
 327 extern char* resource_allocate_bytes(size_t size,
 328     AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
 329 extern char* resource_allocate_bytes(Thread* thread, size_t size,
 330     AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
 331 extern char* resource_reallocate_bytes( char *old, size_t old_size, size_t new_size,
 332     AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
 333 extern void resource_free_bytes( char *old, size_t size );
 334 
 335 //----------------------------------------------------------------------
 336 // Base class for objects allocated in the resource area per default.
 337 // Optionally, objects may be allocated on the C heap with
 338 // new(ResourceObj::C_HEAP) Foo(...) or in an Arena with new (&arena)
 339 // ResourceObj's can be allocated within other objects, but don't use
 340 // new or delete (allocation_type is unknown).  If new is used to allocate,
 341 // use delete to deallocate.
 342 class ResourceObj ALLOCATION_SUPER_CLASS_SPEC {
 343  public:
 344   enum allocation_type { STACK_OR_EMBEDDED = 0, RESOURCE_AREA, C_HEAP, ARENA, allocation_mask = 0x3 };
 345   static void set_allocation_type(address res, allocation_type type) NOT_DEBUG_RETURN;
 346 #ifdef ASSERT
 347  private:
 348   // When this object is allocated on stack the new() operator is not
 349   // called but garbage on stack may look like a valid allocation_type.
 350   // Store negated 'this' pointer when new() is called to distinguish cases.
 351   // Use second array's element for verification value to distinguish garbage.
 352   uintptr_t _allocation_t[2];
 353   bool is_type_set() const;
 354  public:
 355   allocation_type get_allocation_type() const;
 356   bool allocated_on_stack()    const { return get_allocation_type() == STACK_OR_EMBEDDED; }
 357   bool allocated_on_res_area() const { return get_allocation_type() == RESOURCE_AREA; }
 358   bool allocated_on_C_heap()   const { return get_allocation_type() == C_HEAP; }
 359   bool allocated_on_arena()    const { return get_allocation_type() == ARENA; }
 360   ResourceObj(); // default constructor
 361   ResourceObj(const ResourceObj& r); // default copy constructor
 362   ResourceObj& operator=(const ResourceObj& r); // default copy assignment
 363   ~ResourceObj();
 364 #endif // ASSERT
 365 
 366  public:
 367   void* operator new(size_t size, allocation_type type, MEMFLAGS flags) throw();
 368   void* operator new [](size_t size, allocation_type type, MEMFLAGS flags) throw();
 369   void* operator new(size_t size, const std::nothrow_t&  nothrow_constant,
 370       allocation_type type, MEMFLAGS flags) throw();
 371   void* operator new [](size_t size, const std::nothrow_t&  nothrow_constant,
 372       allocation_type type, MEMFLAGS flags) throw();
 373 
 374   void* operator new(size_t size, Arena *arena) throw();
 375 
 376   void* operator new [](size_t size, Arena *arena) throw();
 377 
 378   void* operator new(size_t size) throw() {
 379       address res = (address)resource_allocate_bytes(size);
 380       DEBUG_ONLY(set_allocation_type(res, RESOURCE_AREA);)
 381       return res;
 382   }
 383 
 384   void* operator new(size_t size, const std::nothrow_t& nothrow_constant) throw() {
 385       address res = (address)resource_allocate_bytes(size, AllocFailStrategy::RETURN_NULL);
 386       DEBUG_ONLY(if (res != NULL) set_allocation_type(res, RESOURCE_AREA);)
 387       return res;
 388   }
 389 
 390   void* operator new [](size_t size) throw() {
 391       address res = (address)resource_allocate_bytes(size);
 392       DEBUG_ONLY(set_allocation_type(res, RESOURCE_AREA);)
 393       return res;
 394   }
 395 
 396   void* operator new [](size_t size, const std::nothrow_t& nothrow_constant) throw() {
 397       address res = (address)resource_allocate_bytes(size, AllocFailStrategy::RETURN_NULL);
 398       DEBUG_ONLY(if (res != NULL) set_allocation_type(res, RESOURCE_AREA);)
 399       return res;
 400   }
 401 
 402   void  operator delete(void* p);
 403   void  operator delete [](void* p);
 404 };
 405 
 406 // One of the following macros must be used when allocating an array
 407 // or object to determine whether it should reside in the C heap on in
 408 // the resource area.
 409 
 410 #define NEW_RESOURCE_ARRAY(type, size)\
 411   (type*) resource_allocate_bytes((size) * sizeof(type))
 412 
 413 #define NEW_RESOURCE_ARRAY_RETURN_NULL(type, size)\
 414   (type*) resource_allocate_bytes((size) * sizeof(type), AllocFailStrategy::RETURN_NULL)
 415 
 416 #define NEW_RESOURCE_ARRAY_IN_THREAD(thread, type, size)\
 417   (type*) resource_allocate_bytes(thread, (size) * sizeof(type))
 418 
 419 #define NEW_RESOURCE_ARRAY_IN_THREAD_RETURN_NULL(thread, type, size)\
 420   (type*) resource_allocate_bytes(thread, (size) * sizeof(type), AllocFailStrategy::RETURN_NULL)
 421 
 422 #define REALLOC_RESOURCE_ARRAY(type, old, old_size, new_size)\
 423   (type*) resource_reallocate_bytes((char*)(old), (old_size) * sizeof(type), (new_size) * sizeof(type))
 424 
 425 #define REALLOC_RESOURCE_ARRAY_RETURN_NULL(type, old, old_size, new_size)\
 426   (type*) resource_reallocate_bytes((char*)(old), (old_size) * sizeof(type),\
 427                                     (new_size) * sizeof(type), AllocFailStrategy::RETURN_NULL)
 428 
 429 #define FREE_RESOURCE_ARRAY(type, old, size)\
 430   resource_free_bytes((char*)(old), (size) * sizeof(type))
 431 
 432 #define FREE_FAST(old)\
 433     /* nop */
 434 
 435 #define NEW_RESOURCE_OBJ(type)\
 436   NEW_RESOURCE_ARRAY(type, 1)
 437 
 438 #define NEW_RESOURCE_OBJ_RETURN_NULL(type)\
 439   NEW_RESOURCE_ARRAY_RETURN_NULL(type, 1)
 440 
 441 #define NEW_C_HEAP_ARRAY3(type, size, memflags, pc, allocfail)\
 442   (type*) AllocateHeap((size) * sizeof(type), memflags, pc, allocfail)
 443 
 444 #define NEW_C_HEAP_ARRAY2(type, size, memflags, pc)\
 445   (type*) (AllocateHeap((size) * sizeof(type), memflags, pc))
 446 
 447 #define NEW_C_HEAP_ARRAY(type, size, memflags)\
 448   (type*) (AllocateHeap((size) * sizeof(type), memflags))
 449 
 450 #define NEW_C_HEAP_ARRAY2_RETURN_NULL(type, size, memflags, pc)\
 451   NEW_C_HEAP_ARRAY3(type, (size), memflags, pc, AllocFailStrategy::RETURN_NULL)
 452 
 453 #define NEW_C_HEAP_ARRAY_RETURN_NULL(type, size, memflags)\
 454   NEW_C_HEAP_ARRAY3(type, (size), memflags, CURRENT_PC, AllocFailStrategy::RETURN_NULL)
 455 
 456 #define REALLOC_C_HEAP_ARRAY(type, old, size, memflags)\
 457   (type*) (ReallocateHeap((char*)(old), (size) * sizeof(type), memflags))
 458 
 459 #define REALLOC_C_HEAP_ARRAY_RETURN_NULL(type, old, size, memflags)\
 460   (type*) (ReallocateHeap((char*)(old), (size) * sizeof(type), memflags, AllocFailStrategy::RETURN_NULL))
 461 
 462 #define FREE_C_HEAP_ARRAY(type, old) \
 463   FreeHeap((char*)(old))
 464 
 465 // allocate type in heap without calling ctor
 466 #define NEW_C_HEAP_OBJ(type, memflags)\
 467   NEW_C_HEAP_ARRAY(type, 1, memflags)
 468 
 469 #define NEW_C_HEAP_OBJ_RETURN_NULL(type, memflags)\
 470   NEW_C_HEAP_ARRAY_RETURN_NULL(type, 1, memflags)
 471 
 472 // deallocate obj of type in heap without calling dtor
 473 #define FREE_C_HEAP_OBJ(objname)\
 474   FreeHeap((char*)objname);
 475 
 476 // for statistics
 477 #ifndef PRODUCT
 478 class AllocStats : StackObj {
 479   julong start_mallocs, start_frees;
 480   julong start_malloc_bytes, start_mfree_bytes, start_res_bytes;
 481  public:
 482   AllocStats();
 483 
 484   julong num_mallocs();    // since creation of receiver
 485   julong alloc_bytes();
 486   julong num_frees();
 487   julong free_bytes();
 488   julong resource_bytes();
 489   void   print();
 490 };
 491 #endif
 492 
 493 
 494 //------------------------------ReallocMark---------------------------------
 495 // Code which uses REALLOC_RESOURCE_ARRAY should check an associated
 496 // ReallocMark, which is declared in the same scope as the reallocated
 497 // pointer.  Any operation that could __potentially__ cause a reallocation
 498 // should check the ReallocMark.
 499 class ReallocMark: public StackObj {
 500 protected:
 501   NOT_PRODUCT(int _nesting;)
 502 
 503 public:
 504   ReallocMark()   PRODUCT_RETURN;
 505   void check()    PRODUCT_RETURN;
 506 };
 507 
 508 // Helper class to allocate arrays that may become large.
 509 // Uses the OS malloc for allocations smaller than ArrayAllocatorMallocLimit
 510 // and uses mapped memory for larger allocations.
 511 // Most OS mallocs do something similar but Solaris malloc does not revert
 512 // to mapped memory for large allocations. By default ArrayAllocatorMallocLimit
 513 // is set so that we always use malloc except for Solaris where we set the
 514 // limit to get mapped memory.
 515 template <class E>
 516 class ArrayAllocator : public AllStatic {
 517  private:
 518   static bool should_use_malloc(size_t length);
 519 
 520   static E* allocate_malloc(size_t length, MEMFLAGS flags);
 521   static E* allocate_mmap(size_t length, MEMFLAGS flags);
 522 
 523   static void free_malloc(E* addr, size_t length);
 524   static void free_mmap(E* addr, size_t length);
 525 
 526  public:
 527   static E* allocate(size_t length, MEMFLAGS flags);
 528   static E* reallocate(E* old_addr, size_t old_length, size_t new_length, MEMFLAGS flags);
 529   static void free(E* addr, size_t length);
 530 };
 531 
 532 // Uses mmaped memory for all allocations. All allocations are initially
 533 // zero-filled. No pre-touching.
 534 template <class E>
 535 class MmapArrayAllocator : public AllStatic {
 536  private:
 537   static size_t size_for(size_t length);
 538 
 539  public:
 540   static E* allocate_or_null(size_t length, MEMFLAGS flags);
 541   static E* allocate(size_t length, MEMFLAGS flags);
 542   static void free(E* addr, size_t length);
 543 };
 544 
 545 // Uses malloc:ed memory for all allocations.
 546 template <class E>
 547 class MallocArrayAllocator : public AllStatic {
 548  public:
 549   static size_t size_for(size_t length);
 550 
 551   static E* allocate(size_t length, MEMFLAGS flags);
 552   static void free(E* addr);
 553 };
 554 
 555 #endif // SHARE_VM_MEMORY_ALLOCATION_HPP