1 /*
   2  * Copyright (c) 1997, 2017, 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_RUNTIME_OS_HPP
  26 #define SHARE_VM_RUNTIME_OS_HPP
  27 
  28 #include "jvmtifiles/jvmti.h"
  29 #include "prims/jvm.h"
  30 #include "runtime/extendedPC.hpp"
  31 #include "runtime/handles.hpp"
  32 #include "utilities/macros.hpp"
  33 #include "runtime/osContainer.hpp"
  34 #ifndef _WINDOWS
  35 # include <setjmp.h>
  36 #endif
  37 #ifdef __APPLE__
  38 # include <mach/mach_time.h>
  39 #endif
  40 
  41 class AgentLibrary;
  42 class frame;
  43 
  44 // os defines the interface to operating system; this includes traditional
  45 // OS services (time, I/O) as well as other functionality with system-
  46 // dependent code.
  47 
  48 typedef void (*dll_func)(...);
  49 
  50 class Thread;
  51 class JavaThread;
  52 class Event;
  53 class DLL;
  54 class FileHandle;
  55 class NativeCallStack;
  56 
  57 template<class E> class GrowableArray;
  58 
  59 // %%%%% Moved ThreadState, START_FN, OSThread to new osThread.hpp. -- Rose
  60 
  61 // Platform-independent error return values from OS functions
  62 enum OSReturn {
  63   OS_OK         =  0,        // Operation was successful
  64   OS_ERR        = -1,        // Operation failed
  65   OS_INTRPT     = -2,        // Operation was interrupted
  66   OS_TIMEOUT    = -3,        // Operation timed out
  67   OS_NOMEM      = -5,        // Operation failed for lack of memory
  68   OS_NORESOURCE = -6         // Operation failed for lack of nonmemory resource
  69 };
  70 
  71 enum ThreadPriority {        // JLS 20.20.1-3
  72   NoPriority       = -1,     // Initial non-priority value
  73   MinPriority      =  1,     // Minimum priority
  74   NormPriority     =  5,     // Normal (non-daemon) priority
  75   NearMaxPriority  =  9,     // High priority, used for VMThread
  76   MaxPriority      = 10,     // Highest priority, used for WatcherThread
  77                              // ensures that VMThread doesn't starve profiler
  78   CriticalPriority = 11      // Critical thread priority
  79 };
  80 
  81 // Executable parameter flag for os::commit_memory() and
  82 // os::commit_memory_or_exit().
  83 const bool ExecMem = true;
  84 
  85 // Typedef for structured exception handling support
  86 typedef void (*java_call_t)(JavaValue* value, const methodHandle& method, JavaCallArguments* args, Thread* thread);
  87 
  88 class MallocTracker;
  89 
  90 class os: AllStatic {
  91   friend class VMStructs;
  92   friend class JVMCIVMStructs;
  93   friend class MallocTracker;
  94  public:
  95   enum { page_sizes_max = 9 }; // Size of _page_sizes array (8 plus a sentinel)
  96 
  97  private:
  98   static OSThread*          _starting_thread;
  99   static address            _polling_page;
 100   static volatile int32_t * _mem_serialize_page;
 101   static uintptr_t          _serialize_page_mask;
 102  public:
 103   static size_t             _page_sizes[page_sizes_max];
 104 
 105  private:
 106   static void init_page_sizes(size_t default_page_size) {
 107     _page_sizes[0] = default_page_size;
 108     _page_sizes[1] = 0; // sentinel
 109   }
 110 
 111   static char*  pd_reserve_memory(size_t bytes, char* addr = 0,
 112                                size_t alignment_hint = 0);
 113   static char*  pd_attempt_reserve_memory_at(size_t bytes, char* addr);
 114   static void   pd_split_reserved_memory(char *base, size_t size,
 115                                       size_t split, bool realloc);
 116   static bool   pd_commit_memory(char* addr, size_t bytes, bool executable);
 117   static bool   pd_commit_memory(char* addr, size_t size, size_t alignment_hint,
 118                                  bool executable);
 119   // Same as pd_commit_memory() that either succeeds or calls
 120   // vm_exit_out_of_memory() with the specified mesg.
 121   static void   pd_commit_memory_or_exit(char* addr, size_t bytes,
 122                                          bool executable, const char* mesg);
 123   static void   pd_commit_memory_or_exit(char* addr, size_t size,
 124                                          size_t alignment_hint,
 125                                          bool executable, const char* mesg);
 126   static bool   pd_uncommit_memory(char* addr, size_t bytes);
 127   static bool   pd_release_memory(char* addr, size_t bytes);
 128 
 129   static char*  pd_map_memory(int fd, const char* file_name, size_t file_offset,
 130                            char *addr, size_t bytes, bool read_only = false,
 131                            bool allow_exec = false);
 132   static char*  pd_remap_memory(int fd, const char* file_name, size_t file_offset,
 133                              char *addr, size_t bytes, bool read_only,
 134                              bool allow_exec);
 135   static bool   pd_unmap_memory(char *addr, size_t bytes);
 136   static void   pd_free_memory(char *addr, size_t bytes, size_t alignment_hint);
 137   static void   pd_realign_memory(char *addr, size_t bytes, size_t alignment_hint);
 138 
 139   static size_t page_size_for_region(size_t region_size, size_t min_pages, bool must_be_aligned);
 140 
 141   // Get summary strings for system information in buffer provided
 142   static void  get_summary_cpu_info(char* buf, size_t buflen);
 143   static void  get_summary_os_info(char* buf, size_t buflen);
 144 
 145   static void initialize_initial_active_processor_count();
 146  public:
 147   static void init(void);                      // Called before command line parsing
 148   static void init_before_ergo(void);          // Called after command line parsing
 149                                                // before VM ergonomics processing.
 150   static jint init_2(void);                    // Called after command line parsing
 151                                                // and VM ergonomics processing
 152   static void init_globals(void) {             // Called from init_globals() in init.cpp
 153     init_globals_ext();
 154   }
 155 
 156   // File names are case-insensitive on windows only
 157   // Override me as needed
 158   static int    file_name_strcmp(const char* s1, const char* s2);
 159 
 160   // unset environment variable
 161   static bool unsetenv(const char* name);
 162 
 163   static bool have_special_privileges();
 164 
 165   static jlong  javaTimeMillis();
 166   static jlong  javaTimeNanos();
 167   static void   javaTimeNanos_info(jvmtiTimerInfo *info_ptr);
 168   static void   javaTimeSystemUTC(jlong &seconds, jlong &nanos);
 169   static void   run_periodic_checks();
 170   static bool   supports_monotonic_clock();
 171 
 172   // Returns the elapsed time in seconds since the vm started.
 173   static double elapsedTime();
 174 
 175   // Returns real time in seconds since an arbitrary point
 176   // in the past.
 177   static bool getTimesSecs(double* process_real_time,
 178                            double* process_user_time,
 179                            double* process_system_time);
 180 
 181   // Interface to the performance counter
 182   static jlong elapsed_counter();
 183   static jlong elapsed_frequency();
 184 
 185   // The "virtual time" of a thread is the amount of time a thread has
 186   // actually run.  The first function indicates whether the OS supports
 187   // this functionality for the current thread, and if so:
 188   //   * the second enables vtime tracking (if that is required).
 189   //   * the third tells whether vtime is enabled.
 190   //   * the fourth returns the elapsed virtual time for the current
 191   //     thread.
 192   static bool supports_vtime();
 193   static bool enable_vtime();
 194   static bool vtime_enabled();
 195   static double elapsedVTime();
 196 
 197   // Return current local time in a string (YYYY-MM-DD HH:MM:SS).
 198   // It is MT safe, but not async-safe, as reading time zone
 199   // information may require a lock on some platforms.
 200   static char*      local_time_string(char *buf, size_t buflen);
 201   static struct tm* localtime_pd     (const time_t* clock, struct tm*  res);
 202   static struct tm* gmtime_pd        (const time_t* clock, struct tm*  res);
 203   // Fill in buffer with current local time as an ISO-8601 string.
 204   // E.g., YYYY-MM-DDThh:mm:ss.mmm+zzzz.
 205   // Returns buffer, or NULL if it failed.
 206   static char* iso8601_time(char* buffer, size_t buffer_length, bool utc = false);
 207 
 208   // Interface for detecting multiprocessor system
 209   static inline bool is_MP() {
 210     // During bootstrap if _processor_count is not yet initialized
 211     // we claim to be MP as that is safest. If any platform has a
 212     // stub generator that might be triggered in this phase and for
 213     // which being declared MP when in fact not, is a problem - then
 214     // the bootstrap routine for the stub generator needs to check
 215     // the processor count directly and leave the bootstrap routine
 216     // in place until called after initialization has ocurred.
 217     return (_processor_count != 1) || AssumeMP;
 218   }
 219   static julong available_memory();
 220   static julong physical_memory();
 221   static bool has_allocatable_memory_limit(julong* limit);
 222   static bool is_server_class_machine();
 223 
 224   // number of CPUs
 225   static int processor_count() {
 226     return _processor_count;
 227   }
 228   static void set_processor_count(int count) { _processor_count = count; }
 229 
 230   // Returns the number of CPUs this process is currently allowed to run on.
 231   // Note that on some OSes this can change dynamically.
 232   static int active_processor_count();
 233 
 234   // At startup the number of active CPUs this process is allowed to run on.
 235   // This value does not change dynamically. May be different from active_processor_count().
 236   static int initial_active_processor_count() {
 237     assert(_initial_active_processor_count > 0, "Initial active processor count not set yet.");
 238     return _initial_active_processor_count;
 239   }
 240 
 241   // Bind processes to processors.
 242   //     This is a two step procedure:
 243   //     first you generate a distribution of processes to processors,
 244   //     then you bind processes according to that distribution.
 245   // Compute a distribution for number of processes to processors.
 246   //    Stores the processor id's into the distribution array argument.
 247   //    Returns true if it worked, false if it didn't.
 248   static bool distribute_processes(uint length, uint* distribution);
 249   // Binds the current process to a processor.
 250   //    Returns true if it worked, false if it didn't.
 251   static bool bind_to_processor(uint processor_id);
 252 
 253   // Give a name to the current thread.
 254   static void set_native_thread_name(const char *name);
 255 
 256   // Interface for stack banging (predetect possible stack overflow for
 257   // exception processing)  There are guard pages, and above that shadow
 258   // pages for stack overflow checking.
 259   static bool uses_stack_guard_pages();
 260   static bool must_commit_stack_guard_pages();
 261   static void map_stack_shadow_pages(address sp);
 262   static bool stack_shadow_pages_available(Thread *thread, const methodHandle& method, address sp);
 263 
 264   // OS interface to Virtual Memory
 265 
 266   // Return the default page size.
 267   static int    vm_page_size();
 268 
 269   // Returns the page size to use for a region of memory.
 270   // region_size / min_pages will always be greater than or equal to the
 271   // returned value. The returned value will divide region_size.
 272   static size_t page_size_for_region_aligned(size_t region_size, size_t min_pages);
 273 
 274   // Returns the page size to use for a region of memory.
 275   // region_size / min_pages will always be greater than or equal to the
 276   // returned value. The returned value might not divide region_size.
 277   static size_t page_size_for_region_unaligned(size_t region_size, size_t min_pages);
 278 
 279   // Return the largest page size that can be used
 280   static size_t max_page_size() {
 281     // The _page_sizes array is sorted in descending order.
 282     return _page_sizes[0];
 283   }
 284 
 285   // Methods for tracing page sizes returned by the above method.
 286   // The region_{min,max}_size parameters should be the values
 287   // passed to page_size_for_region() and page_size should be the result of that
 288   // call.  The (optional) base and size parameters should come from the
 289   // ReservedSpace base() and size() methods.
 290   static void trace_page_sizes(const char* str, const size_t* page_sizes, int count);
 291   static void trace_page_sizes(const char* str,
 292                                const size_t region_min_size,
 293                                const size_t region_max_size,
 294                                const size_t page_size,
 295                                const char* base,
 296                                const size_t size);
 297   static void trace_page_sizes_for_requested_size(const char* str,
 298                                                   const size_t requested_size,
 299                                                   const size_t page_size,
 300                                                   const size_t alignment,
 301                                                   const char* base,
 302                                                   const size_t size);
 303 
 304   static int    vm_allocation_granularity();
 305   static char*  reserve_memory(size_t bytes, char* addr = 0,
 306                                size_t alignment_hint = 0);
 307   static char*  reserve_memory(size_t bytes, char* addr,
 308                                size_t alignment_hint, MEMFLAGS flags);
 309   static char*  reserve_memory_aligned(size_t size, size_t alignment);
 310   static char*  attempt_reserve_memory_at(size_t bytes, char* addr);
 311   static void   split_reserved_memory(char *base, size_t size,
 312                                       size_t split, bool realloc);
 313   static bool   commit_memory(char* addr, size_t bytes, bool executable);
 314   static bool   commit_memory(char* addr, size_t size, size_t alignment_hint,
 315                               bool executable);
 316   // Same as commit_memory() that either succeeds or calls
 317   // vm_exit_out_of_memory() with the specified mesg.
 318   static void   commit_memory_or_exit(char* addr, size_t bytes,
 319                                       bool executable, const char* mesg);
 320   static void   commit_memory_or_exit(char* addr, size_t size,
 321                                       size_t alignment_hint,
 322                                       bool executable, const char* mesg);
 323   static bool   uncommit_memory(char* addr, size_t bytes);
 324   static bool   release_memory(char* addr, size_t bytes);
 325 
 326   // Touch memory pages that cover the memory range from start to end (exclusive)
 327   // to make the OS back the memory range with actual memory.
 328   // Current implementation may not touch the last page if unaligned addresses
 329   // are passed.
 330   static void   pretouch_memory(void* start, void* end, size_t page_size = vm_page_size());
 331 
 332   enum ProtType { MEM_PROT_NONE, MEM_PROT_READ, MEM_PROT_RW, MEM_PROT_RWX };
 333   static bool   protect_memory(char* addr, size_t bytes, ProtType prot,
 334                                bool is_committed = true);
 335 
 336   static bool   guard_memory(char* addr, size_t bytes);
 337   static bool   unguard_memory(char* addr, size_t bytes);
 338   static bool   create_stack_guard_pages(char* addr, size_t bytes);
 339   static bool   pd_create_stack_guard_pages(char* addr, size_t bytes);
 340   static bool   remove_stack_guard_pages(char* addr, size_t bytes);
 341 
 342   static char*  map_memory(int fd, const char* file_name, size_t file_offset,
 343                            char *addr, size_t bytes, bool read_only = false,
 344                            bool allow_exec = false);
 345   static char*  remap_memory(int fd, const char* file_name, size_t file_offset,
 346                              char *addr, size_t bytes, bool read_only,
 347                              bool allow_exec);
 348   static bool   unmap_memory(char *addr, size_t bytes);
 349   static void   free_memory(char *addr, size_t bytes, size_t alignment_hint);
 350   static void   realign_memory(char *addr, size_t bytes, size_t alignment_hint);
 351 
 352   // NUMA-specific interface
 353   static bool   numa_has_static_binding();
 354   static bool   numa_has_group_homing();
 355   static void   numa_make_local(char *addr, size_t bytes, int lgrp_hint);
 356   static void   numa_make_global(char *addr, size_t bytes);
 357   static size_t numa_get_groups_num();
 358   static size_t numa_get_leaf_groups(int *ids, size_t size);
 359   static bool   numa_topology_changed();
 360   static int    numa_get_group_id();
 361 
 362   // Page manipulation
 363   struct page_info {
 364     size_t size;
 365     int lgrp_id;
 366   };
 367   static bool   get_page_info(char *start, page_info* info);
 368   static char*  scan_pages(char *start, char* end, page_info* page_expected, page_info* page_found);
 369 
 370   static char*  non_memory_address_word();
 371   // reserve, commit and pin the entire memory region
 372   static char*  reserve_memory_special(size_t size, size_t alignment,
 373                                        char* addr, bool executable);
 374   static bool   release_memory_special(char* addr, size_t bytes);
 375   static void   large_page_init();
 376   static size_t large_page_size();
 377   static bool   can_commit_large_page_memory();
 378   static bool   can_execute_large_page_memory();
 379 
 380   // OS interface to polling page
 381   static address get_polling_page()             { return _polling_page; }
 382   static void    set_polling_page(address page) { _polling_page = page; }
 383   static bool    is_poll_address(address addr)  { return addr >= _polling_page && addr < (_polling_page + os::vm_page_size()); }
 384   static void    make_polling_page_unreadable();
 385   static void    make_polling_page_readable();
 386 
 387   // Routines used to serialize the thread state without using membars
 388   static void    serialize_thread_states();
 389 
 390   // Since we write to the serialize page from every thread, we
 391   // want stores to be on unique cache lines whenever possible
 392   // in order to minimize CPU cross talk.  We pre-compute the
 393   // amount to shift the thread* to make this offset unique to
 394   // each thread.
 395   static int     get_serialize_page_shift_count() {
 396     return SerializePageShiftCount;
 397   }
 398 
 399   static void     set_serialize_page_mask(uintptr_t mask) {
 400     _serialize_page_mask = mask;
 401   }
 402 
 403   static unsigned int  get_serialize_page_mask() {
 404     return _serialize_page_mask;
 405   }
 406 
 407   static void    set_memory_serialize_page(address page);
 408 
 409   static address get_memory_serialize_page() {
 410     return (address)_mem_serialize_page;
 411   }
 412 
 413   static inline void write_memory_serialize_page(JavaThread *thread) {
 414     uintptr_t page_offset = ((uintptr_t)thread >>
 415                             get_serialize_page_shift_count()) &
 416                             get_serialize_page_mask();
 417     *(volatile int32_t *)((uintptr_t)_mem_serialize_page+page_offset) = 1;
 418   }
 419 
 420   static bool    is_memory_serialize_page(JavaThread *thread, address addr) {
 421     if (UseMembar) return false;
 422     // Previously this function calculated the exact address of this
 423     // thread's serialize page, and checked if the faulting address
 424     // was equal.  However, some platforms mask off faulting addresses
 425     // to the page size, so now we just check that the address is
 426     // within the page.  This makes the thread argument unnecessary,
 427     // but we retain the NULL check to preserve existing behavior.
 428     if (thread == NULL) return false;
 429     address page = (address) _mem_serialize_page;
 430     return addr >= page && addr < (page + os::vm_page_size());
 431   }
 432 
 433   static void block_on_serialize_page_trap();
 434 
 435   // threads
 436 
 437   enum ThreadType {
 438     vm_thread,
 439     cgc_thread,        // Concurrent GC thread
 440     pgc_thread,        // Parallel GC thread
 441     java_thread,       // Java, CodeCacheSweeper, JVMTIAgent and Service threads.
 442     compiler_thread,
 443     watcher_thread,
 444     os_thread
 445   };
 446 
 447   static bool create_thread(Thread* thread,
 448                             ThreadType thr_type,
 449                             size_t req_stack_size = 0);
 450   static bool create_main_thread(JavaThread* thread);
 451   static bool create_attached_thread(JavaThread* thread);
 452   static void pd_start_thread(Thread* thread);
 453   static void start_thread(Thread* thread);
 454 
 455   static void initialize_thread(Thread* thr);
 456   static void free_thread(OSThread* osthread);
 457 
 458   // thread id on Linux/64bit is 64bit, on Windows and Solaris, it's 32bit
 459   static intx current_thread_id();
 460   static int current_process_id();
 461   static int sleep(Thread* thread, jlong ms, bool interruptable);
 462   // Short standalone OS sleep suitable for slow path spin loop.
 463   // Ignores Thread.interrupt() (so keep it short).
 464   // ms = 0, will sleep for the least amount of time allowed by the OS.
 465   static void naked_short_sleep(jlong ms);
 466   static void infinite_sleep(); // never returns, use with CAUTION
 467   static void naked_yield () ;
 468   static OSReturn set_priority(Thread* thread, ThreadPriority priority);
 469   static OSReturn get_priority(const Thread* const thread, ThreadPriority& priority);
 470 
 471   static void interrupt(Thread* thread);
 472   static bool is_interrupted(Thread* thread, bool clear_interrupted);
 473 
 474   static int pd_self_suspend_thread(Thread* thread);
 475 
 476   static ExtendedPC fetch_frame_from_context(const void* ucVoid, intptr_t** sp, intptr_t** fp);
 477   static frame      fetch_frame_from_context(const void* ucVoid);
 478   static frame      fetch_frame_from_ucontext(Thread* thread, void* ucVoid);
 479 
 480   static void breakpoint();
 481   static bool start_debugging(char *buf, int buflen);
 482 
 483   static address current_stack_pointer();
 484   static address current_stack_base();
 485   static size_t current_stack_size();
 486 
 487   static void verify_stack_alignment() PRODUCT_RETURN;
 488 
 489   static bool message_box(const char* title, const char* message);
 490   static char* do_you_want_to_debug(const char* message);
 491 
 492   // run cmd in a separate process and return its exit code; or -1 on failures
 493   static int fork_and_exec(char *cmd);
 494 
 495   // Call ::exit() on all platforms but Windows
 496   static void exit(int num);
 497 
 498   // Terminate the VM, but don't exit the process
 499   static void shutdown();
 500 
 501   // Terminate with an error.  Default is to generate a core file on platforms
 502   // that support such things.  This calls shutdown() and then aborts.
 503   static void abort(bool dump_core, void *siginfo, const void *context);
 504   static void abort(bool dump_core = true);
 505 
 506   // Die immediately, no exit hook, no abort hook, no cleanup.
 507   static void die();
 508 
 509   // File i/o operations
 510   static const int default_file_open_flags();
 511   static int open(const char *path, int oflag, int mode);
 512   static FILE* open(int fd, const char* mode);
 513   static int close(int fd);
 514   static jlong lseek(int fd, jlong offset, int whence);
 515   static char* native_path(char *path);
 516   static int ftruncate(int fd, jlong length);
 517   static int fsync(int fd);
 518   static int available(int fd, jlong *bytes);
 519   static int get_fileno(FILE* fp);
 520   static void flockfile(FILE* fp);
 521   static void funlockfile(FILE* fp);
 522 
 523   static int compare_file_modified_times(const char* file1, const char* file2);
 524 
 525   //File i/o operations
 526 
 527   static size_t read(int fd, void *buf, unsigned int nBytes);
 528   static size_t read_at(int fd, void *buf, unsigned int nBytes, jlong offset);
 529   static size_t restartable_read(int fd, void *buf, unsigned int nBytes);
 530   static size_t write(int fd, const void *buf, unsigned int nBytes);
 531 
 532   // Reading directories.
 533   static DIR*           opendir(const char* dirname);
 534   static int            readdir_buf_size(const char *path);
 535   static struct dirent* readdir(DIR* dirp, dirent* dbuf);
 536   static int            closedir(DIR* dirp);
 537 
 538   // Dynamic library extension
 539   static const char*    dll_file_extension();
 540 
 541   static const char*    get_temp_directory();
 542   static const char*    get_current_directory(char *buf, size_t buflen);
 543 
 544   // Builds the platform-specific name of a library.
 545   // Returns false if the buffer is too small.
 546   static bool           dll_build_name(char* buffer, size_t size,
 547                                        const char* fname);
 548 
 549   // Builds a platform-specific full library path given an ld path and
 550   // unadorned library name. Returns true if the buffer contains a full
 551   // path to an existing file, false otherwise. If pathname is empty,
 552   // uses the path to the current directory.
 553   static bool           dll_locate_lib(char* buffer, size_t size,
 554                                        const char* pathname, const char* fname);
 555 
 556   // Symbol lookup, find nearest function name; basically it implements
 557   // dladdr() for all platforms. Name of the nearest function is copied
 558   // to buf. Distance from its base address is optionally returned as offset.
 559   // If function name is not found, buf[0] is set to '\0' and offset is
 560   // set to -1 (if offset is non-NULL).
 561   static bool dll_address_to_function_name(address addr, char* buf,
 562                                            int buflen, int* offset,
 563                                            bool demangle = true);
 564 
 565   // Locate DLL/DSO. On success, full path of the library is copied to
 566   // buf, and offset is optionally set to be the distance between addr
 567   // and the library's base address. On failure, buf[0] is set to '\0'
 568   // and offset is set to -1 (if offset is non-NULL).
 569   static bool dll_address_to_library_name(address addr, char* buf,
 570                                           int buflen, int* offset);
 571 
 572   // Find out whether the pc is in the static code for jvm.dll/libjvm.so.
 573   static bool address_is_in_vm(address addr);
 574 
 575   // Loads .dll/.so and
 576   // in case of error it checks if .dll/.so was built for the
 577   // same architecture as HotSpot is running on
 578   static void* dll_load(const char *name, char *ebuf, int ebuflen);
 579 
 580   // lookup symbol in a shared library
 581   static void* dll_lookup(void* handle, const char* name);
 582 
 583   // Unload library
 584   static void  dll_unload(void *lib);
 585 
 586   // Callback for loaded module information
 587   // Input parameters:
 588   //    char*     module_file_name,
 589   //    address   module_base_addr,
 590   //    address   module_top_addr,
 591   //    void*     param
 592   typedef int (*LoadedModulesCallbackFunc)(const char *, address, address, void *);
 593 
 594   static int get_loaded_modules_info(LoadedModulesCallbackFunc callback, void *param);
 595 
 596   // Return the handle of this process
 597   static void* get_default_process_handle();
 598 
 599   // Check for static linked agent library
 600   static bool find_builtin_agent(AgentLibrary *agent_lib, const char *syms[],
 601                                  size_t syms_len);
 602 
 603   // Find agent entry point
 604   static void *find_agent_function(AgentLibrary *agent_lib, bool check_lib,
 605                                    const char *syms[], size_t syms_len);
 606 
 607   // Write to stream
 608   static int log_vsnprintf(char* buf, size_t len, const char* fmt, va_list args) ATTRIBUTE_PRINTF(3, 0);
 609 
 610   // Get host name in buffer provided
 611   static bool get_host_name(char* buf, size_t buflen);
 612 
 613   // Print out system information; they are called by fatal error handler.
 614   // Output format may be different on different platforms.
 615   static void print_os_info(outputStream* st);
 616   static void print_os_info_brief(outputStream* st);
 617   static void print_cpu_info(outputStream* st, char* buf, size_t buflen);
 618   static void pd_print_cpu_info(outputStream* st, char* buf, size_t buflen);
 619   static void print_summary_info(outputStream* st, char* buf, size_t buflen);
 620   static void print_memory_info(outputStream* st);
 621   static void print_dll_info(outputStream* st);
 622   static void print_environment_variables(outputStream* st, const char** env_list);
 623   static void print_context(outputStream* st, const void* context);
 624   static void print_register_info(outputStream* st, const void* context);
 625   static void print_siginfo(outputStream* st, const void* siginfo);
 626   static void print_signal_handlers(outputStream* st, char* buf, size_t buflen);
 627   static void print_date_and_time(outputStream* st, char* buf, size_t buflen);
 628 
 629   static void print_location(outputStream* st, intptr_t x, bool verbose = false);
 630   static size_t lasterror(char *buf, size_t len);
 631   static int get_last_error();
 632 
 633   // Replacement for strerror().
 634   // Will return the english description of the error (e.g. "File not found", as
 635   //  suggested in the POSIX standard.
 636   // Will return "Unknown error" for an unknown errno value.
 637   // Will not attempt to localize the returned string.
 638   // Will always return a valid string which is a static constant.
 639   // Will not change the value of errno.
 640   static const char* strerror(int e);
 641 
 642   // Will return the literalized version of the given errno (e.g. "EINVAL"
 643   //  for EINVAL).
 644   // Will return "Unknown error" for an unknown errno value.
 645   // Will always return a valid string which is a static constant.
 646   // Will not change the value of errno.
 647   static const char* errno_name(int e);
 648 
 649   // Determines whether the calling process is being debugged by a user-mode debugger.
 650   static bool is_debugger_attached();
 651 
 652   // wait for a key press if PauseAtExit is set
 653   static void wait_for_keypress_at_exit(void);
 654 
 655   // The following two functions are used by fatal error handler to trace
 656   // native (C) frames. They are not part of frame.hpp/frame.cpp because
 657   // frame.hpp/cpp assume thread is JavaThread, and also because different
 658   // OS/compiler may have different convention or provide different API to
 659   // walk C frames.
 660   //
 661   // We don't attempt to become a debugger, so we only follow frames if that
 662   // does not require a lookup in the unwind table, which is part of the binary
 663   // file but may be unsafe to read after a fatal error. So on x86, we can
 664   // only walk stack if %ebp is used as frame pointer; on ia64, it's not
 665   // possible to walk C stack without having the unwind table.
 666   static bool is_first_C_frame(frame *fr);
 667   static frame get_sender_for_C_frame(frame *fr);
 668 
 669   // return current frame. pc() and sp() are set to NULL on failure.
 670   static frame      current_frame();
 671 
 672   static void print_hex_dump(outputStream* st, address start, address end, int unitsize);
 673 
 674   // returns a string to describe the exception/signal;
 675   // returns NULL if exception_code is not an OS exception/signal.
 676   static const char* exception_name(int exception_code, char* buf, size_t buflen);
 677 
 678   // Returns the signal number (e.g. 11) for a given signal name (SIGSEGV).
 679   static int get_signal_number(const char* signal_name);
 680 
 681   // Returns native Java library, loads if necessary
 682   static void*    native_java_library();
 683 
 684   // Fills in path to jvm.dll/libjvm.so (used by the Disassembler)
 685   static void     jvm_path(char *buf, jint buflen);
 686 
 687   // Returns true if we are running in a headless jre.
 688   static bool     is_headless_jre();
 689 
 690   // JNI names
 691   static void     print_jni_name_prefix_on(outputStream* st, int args_size);
 692   static void     print_jni_name_suffix_on(outputStream* st, int args_size);
 693 
 694   // Init os specific system properties values
 695   static void init_system_properties_values();
 696 
 697   // IO operations, non-JVM_ version.
 698   static int stat(const char* path, struct stat* sbuf);
 699   static bool dir_is_empty(const char* path);
 700 
 701   // IO operations on binary files
 702   static int create_binary_file(const char* path, bool rewrite_existing);
 703   static jlong current_file_offset(int fd);
 704   static jlong seek_to_file_offset(int fd, jlong offset);
 705 
 706   // Retrieve native stack frames.
 707   // Parameter:
 708   //   stack:  an array to storage stack pointers.
 709   //   frames: size of above array.
 710   //   toSkip: number of stack frames to skip at the beginning.
 711   // Return: number of stack frames captured.
 712   static int get_native_stack(address* stack, int size, int toSkip = 0);
 713 
 714   // General allocation (must be MT-safe)
 715   static void* malloc  (size_t size, MEMFLAGS flags, const NativeCallStack& stack);
 716   static void* malloc  (size_t size, MEMFLAGS flags);
 717   static void* realloc (void *memblock, size_t size, MEMFLAGS flag, const NativeCallStack& stack);
 718   static void* realloc (void *memblock, size_t size, MEMFLAGS flag);
 719 
 720   static void  free    (void *memblock);
 721   static char* strdup(const char *, MEMFLAGS flags = mtInternal);  // Like strdup
 722   // Like strdup, but exit VM when strdup() returns NULL
 723   static char* strdup_check_oom(const char*, MEMFLAGS flags = mtInternal);
 724 
 725 #ifndef PRODUCT
 726   static julong num_mallocs;         // # of calls to malloc/realloc
 727   static julong alloc_bytes;         // # of bytes allocated
 728   static julong num_frees;           // # of calls to free
 729   static julong free_bytes;          // # of bytes freed
 730 #endif
 731 
 732   // SocketInterface (ex HPI SocketInterface )
 733   static int socket(int domain, int type, int protocol);
 734   static int socket_close(int fd);
 735   static int recv(int fd, char* buf, size_t nBytes, uint flags);
 736   static int send(int fd, char* buf, size_t nBytes, uint flags);
 737   static int raw_send(int fd, char* buf, size_t nBytes, uint flags);
 738   static int connect(int fd, struct sockaddr* him, socklen_t len);
 739   static struct hostent* get_host_by_name(char* name);
 740 
 741   // Support for signals (see JVM_RaiseSignal, JVM_RegisterSignal)
 742   static void  signal_init(TRAPS);
 743   static void  signal_init_pd();
 744   static void  signal_notify(int signal_number);
 745   static void* signal(int signal_number, void* handler);
 746   static void  signal_raise(int signal_number);
 747   static int   signal_wait();
 748   static int   signal_lookup();
 749   static void* user_handler();
 750   static void  terminate_signal_thread();
 751   static int   sigexitnum_pd();
 752 
 753   // random number generation
 754   static int random();                     // return 32bit pseudorandom number
 755   static void init_random(unsigned int initval);    // initialize random sequence
 756 
 757   // Structured OS Exception support
 758   static void os_exception_wrapper(java_call_t f, JavaValue* value, const methodHandle& method, JavaCallArguments* args, Thread* thread);
 759 
 760   // On Posix compatible OS it will simply check core dump limits while on Windows
 761   // it will check if dump file can be created. Check or prepare a core dump to be
 762   // taken at a later point in the same thread in os::abort(). Use the caller
 763   // provided buffer as a scratch buffer. The status message which will be written
 764   // into the error log either is file location or a short error message, depending
 765   // on the checking result.
 766   static void check_dump_limit(char* buffer, size_t bufferSize);
 767 
 768   // Get the default path to the core file
 769   // Returns the length of the string
 770   static int get_core_path(char* buffer, size_t bufferSize);
 771 
 772   // JVMTI & JVM monitoring and management support
 773   // The thread_cpu_time() and current_thread_cpu_time() are only
 774   // supported if is_thread_cpu_time_supported() returns true.
 775   // They are not supported on Solaris T1.
 776 
 777   // Thread CPU Time - return the fast estimate on a platform
 778   // On Solaris - call gethrvtime (fast) - user time only
 779   // On Linux   - fast clock_gettime where available - user+sys
 780   //            - otherwise: very slow /proc fs - user+sys
 781   // On Windows - GetThreadTimes - user+sys
 782   static jlong current_thread_cpu_time();
 783   static jlong thread_cpu_time(Thread* t);
 784 
 785   // Thread CPU Time with user_sys_cpu_time parameter.
 786   //
 787   // If user_sys_cpu_time is true, user+sys time is returned.
 788   // Otherwise, only user time is returned
 789   static jlong current_thread_cpu_time(bool user_sys_cpu_time);
 790   static jlong thread_cpu_time(Thread* t, bool user_sys_cpu_time);
 791 
 792   // Return a bunch of info about the timers.
 793   // Note that the returned info for these two functions may be different
 794   // on some platforms
 795   static void current_thread_cpu_time_info(jvmtiTimerInfo *info_ptr);
 796   static void thread_cpu_time_info(jvmtiTimerInfo *info_ptr);
 797 
 798   static bool is_thread_cpu_time_supported();
 799 
 800   // System loadavg support.  Returns -1 if load average cannot be obtained.
 801   static int loadavg(double loadavg[], int nelem);
 802 
 803   // Hook for os specific jvm options that we don't want to abort on seeing
 804   static bool obsolete_option(const JavaVMOption *option);
 805 
 806   // Amount beyond the callee frame size that we bang the stack.
 807   static int extra_bang_size_in_bytes();
 808 
 809   static char** split_path(const char* path, int* n);
 810 
 811   // Extensions
 812 #include "runtime/os_ext.hpp"
 813 
 814  public:
 815   class CrashProtectionCallback : public StackObj {
 816   public:
 817     virtual void call() = 0;
 818   };
 819 
 820   // Platform dependent stuff
 821 #ifndef _WINDOWS
 822 # include "os_posix.hpp"
 823 #endif
 824 #include OS_CPU_HEADER(os)
 825 #include OS_HEADER(os)
 826 
 827 #ifndef OS_NATIVE_THREAD_CREATION_FAILED_MSG
 828 #define OS_NATIVE_THREAD_CREATION_FAILED_MSG "unable to create native thread: possibly out of memory or process/resource limits reached"
 829 #endif
 830 
 831  public:
 832 #ifndef PLATFORM_PRINT_NATIVE_STACK
 833   // No platform-specific code for printing the native stack.
 834   static bool platform_print_native_stack(outputStream* st, const void* context,
 835                                           char *buf, int buf_size) {
 836     return false;
 837   }
 838 #endif
 839 
 840   // debugging support (mostly used by debug.cpp but also fatal error handler)
 841   static bool find(address pc, outputStream* st = tty); // OS specific function to make sense out of an address
 842 
 843   static bool dont_yield();                     // when true, JVM_Yield() is nop
 844   static void print_statistics();
 845 
 846   // Thread priority helpers (implemented in OS-specific part)
 847   static OSReturn set_native_priority(Thread* thread, int native_prio);
 848   static OSReturn get_native_priority(const Thread* const thread, int* priority_ptr);
 849   static int java_to_os_priority[CriticalPriority + 1];
 850   // Hint to the underlying OS that a task switch would not be good.
 851   // Void return because it's a hint and can fail.
 852   static void hint_no_preempt();
 853   static const char* native_thread_creation_failed_msg() {
 854     return OS_NATIVE_THREAD_CREATION_FAILED_MSG;
 855   }
 856 
 857   // Used at creation if requested by the diagnostic flag PauseAtStartup.
 858   // Causes the VM to wait until an external stimulus has been applied
 859   // (for Unix, that stimulus is a signal, for Windows, an external
 860   // ResumeThread call)
 861   static void pause();
 862 
 863   // Builds a platform dependent Agent_OnLoad_<libname> function name
 864   // which is used to find statically linked in agents.
 865   static char*  build_agent_function_name(const char *sym, const char *cname,
 866                                           bool is_absolute_path);
 867 
 868   class SuspendedThreadTaskContext {
 869   public:
 870     SuspendedThreadTaskContext(Thread* thread, void *ucontext) : _thread(thread), _ucontext(ucontext) {}
 871     Thread* thread() const { return _thread; }
 872     void* ucontext() const { return _ucontext; }
 873   private:
 874     Thread* _thread;
 875     void* _ucontext;
 876   };
 877 
 878   class SuspendedThreadTask {
 879   public:
 880     SuspendedThreadTask(Thread* thread) : _thread(thread), _done(false) {}
 881     virtual ~SuspendedThreadTask() {}
 882     void run();
 883     bool is_done() { return _done; }
 884     virtual void do_task(const SuspendedThreadTaskContext& context) = 0;
 885   protected:
 886   private:
 887     void internal_do_task();
 888     Thread* _thread;
 889     bool _done;
 890   };
 891 
 892 #ifndef _WINDOWS
 893   // Suspend/resume support
 894   // Protocol:
 895   //
 896   // a thread starts in SR_RUNNING
 897   //
 898   // SR_RUNNING can go to
 899   //   * SR_SUSPEND_REQUEST when the WatcherThread wants to suspend it
 900   // SR_SUSPEND_REQUEST can go to
 901   //   * SR_RUNNING if WatcherThread decides it waited for SR_SUSPENDED too long (timeout)
 902   //   * SR_SUSPENDED if the stopped thread receives the signal and switches state
 903   // SR_SUSPENDED can go to
 904   //   * SR_WAKEUP_REQUEST when the WatcherThread has done the work and wants to resume
 905   // SR_WAKEUP_REQUEST can go to
 906   //   * SR_RUNNING when the stopped thread receives the signal
 907   //   * SR_WAKEUP_REQUEST on timeout (resend the signal and try again)
 908   class SuspendResume {
 909    public:
 910     enum State {
 911       SR_RUNNING,
 912       SR_SUSPEND_REQUEST,
 913       SR_SUSPENDED,
 914       SR_WAKEUP_REQUEST
 915     };
 916 
 917   private:
 918     volatile State _state;
 919 
 920   private:
 921     /* try to switch state from state "from" to state "to"
 922      * returns the state set after the method is complete
 923      */
 924     State switch_state(State from, State to);
 925 
 926   public:
 927     SuspendResume() : _state(SR_RUNNING) { }
 928 
 929     State state() const { return _state; }
 930 
 931     State request_suspend() {
 932       return switch_state(SR_RUNNING, SR_SUSPEND_REQUEST);
 933     }
 934 
 935     State cancel_suspend() {
 936       return switch_state(SR_SUSPEND_REQUEST, SR_RUNNING);
 937     }
 938 
 939     State suspended() {
 940       return switch_state(SR_SUSPEND_REQUEST, SR_SUSPENDED);
 941     }
 942 
 943     State request_wakeup() {
 944       return switch_state(SR_SUSPENDED, SR_WAKEUP_REQUEST);
 945     }
 946 
 947     State running() {
 948       return switch_state(SR_WAKEUP_REQUEST, SR_RUNNING);
 949     }
 950 
 951     bool is_running() const {
 952       return _state == SR_RUNNING;
 953     }
 954 
 955     bool is_suspend_request() const {
 956       return _state == SR_SUSPEND_REQUEST;
 957     }
 958 
 959     bool is_suspended() const {
 960       return _state == SR_SUSPENDED;
 961     }
 962   };
 963 #endif // !WINDOWS
 964 
 965 
 966  protected:
 967   static volatile unsigned int _rand_seed;    // seed for random number generator
 968   static int _processor_count;                // number of processors
 969   static int _initial_active_processor_count; // number of active processors during initialization.
 970 
 971   static char* format_boot_path(const char* format_string,
 972                                 const char* home,
 973                                 int home_len,
 974                                 char fileSep,
 975                                 char pathSep);
 976   static bool set_boot_path(char fileSep, char pathSep);
 977 
 978 };
 979 
 980 // Note that "PAUSE" is almost always used with synchronization
 981 // so arguably we should provide Atomic::SpinPause() instead
 982 // of the global SpinPause() with C linkage.
 983 // It'd also be eligible for inlining on many platforms.
 984 
 985 extern "C" int SpinPause();
 986 
 987 #endif // SHARE_VM_RUNTIME_OS_HPP