Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright (c) 1997, 2011, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  *

  */

 #ifndef SHARE_VM_RUNTIME_OS_HPP

 #define SHARE_VM_RUNTIME_OS_HPP

 #include "jvmtifiles/jvmti.h"

 #include "runtime/atomic.hpp"

 #include "runtime/extendedPC.hpp"

 #include "runtime/handles.hpp"

 #include "utilities/top.hpp"

 #ifdef TARGET_OS_FAMILY_linux

 # include "jvm_linux.h"

 #endif

 #ifdef TARGET_OS_FAMILY_solaris

 # include "jvm_solaris.h"

 #endif

 #ifdef TARGET_OS_FAMILY_windows

 # include "jvm_windows.h"

 #endif

 // os defines the interface to operating system; this includes traditional

 // OS services (time, I/O) as well as other functionality with system-

 // dependent code.

 typedef void (*dll_func)(...);

 class Thread;

 class JavaThread;

 class Event;

 class DLL;

 class FileHandle;

 template<class E> class GrowableArray;

 // %%%%% Moved ThreadState, START_FN, OSThread to new osThread.hpp. -- Rose

 // Platform-independent error return values from OS functions

 enum OSReturn {

   OS_OK         =  0,        // Operation was successful

   OS_ERR        = -1,        // Operation failed

   OS_INTRPT     = -2,        // Operation was interrupted

   OS_TIMEOUT    = -3,        // Operation timed out

   OS_NOMEM      = -5,        // Operation failed for lack of memory

   OS_NORESOURCE = -6         // Operation failed for lack of nonmemory resource

 };

 enum ThreadPriority {        // JLS 20.20.1-3

   NoPriority       = -1,     // Initial non-priority value

   MinPriority      =  1,     // Minimum priority

   NormPriority     =  5,     // Normal (non-daemon) priority

   NearMaxPriority  =  9,     // High priority, used for VMThread

   MaxPriority      = 10      // Highest priority, used for WatcherThread

                              // ensures that VMThread doesn't starve profiler

 };

 // Typedef for structured exception handling support

 typedef void (*java_call_t)(JavaValue* value, methodHandle* method, JavaCallArguments* args, Thread* thread);

 class os: AllStatic {

  public:

   enum { page_sizes_max = 9 }; // Size of _page_sizes array (8 plus a sentinel)

  private:

   static OSThread*          _starting_thread;

   static address            _polling_page;

   static volatile int32_t * _mem_serialize_page;

   static uintptr_t          _serialize_page_mask;

  public:

   static size_t             _page_sizes[page_sizes_max];

  private:

   static void init_page_sizes(size_t default_page_size) {

     _page_sizes[0] = default_page_size;

     _page_sizes[1] = 0; // sentinel

   }

  public:

   static void init(void);                      // Called before command line parsing

   static jint init_2(void);                    // Called after command line parsing

   static void init_3(void);                    // Called at the end of vm init

   // File names are case-insensitive on windows only

   // Override me as needed

   static int    file_name_strcmp(const char* s1, const char* s2);

   static bool getenv(const char* name, char* buffer, int len);

   static bool have_special_privileges();

   static jlong  javaTimeMillis();

   static jlong  javaTimeNanos();

   static void   javaTimeNanos_info(jvmtiTimerInfo *info_ptr);

   static void   run_periodic_checks();

   // Returns the elapsed time in seconds since the vm started.

   static double elapsedTime();

   // Returns real time in seconds since an arbitrary point

   // in the past.

   static bool getTimesSecs(double* process_real_time,

                            double* process_user_time,

                            double* process_system_time);

   // Interface to the performance counter

   static jlong elapsed_counter();

   static jlong elapsed_frequency();

   // The "virtual time" of a thread is the amount of time a thread has

   // actually run.  The first function indicates whether the OS supports

   // this functionality for the current thread, and if so:

   //   * the second enables vtime tracking (if that is required).

   //   * the third tells whether vtime is enabled.

   //   * the fourth returns the elapsed virtual time for the current

   //     thread.

   static bool supports_vtime();

   static bool enable_vtime();

   static bool vtime_enabled();

   static double elapsedVTime();

   // Return current local time in a string (YYYY-MM-DD HH:MM:SS).

   // It is MT safe, but not async-safe, as reading time zone

   // information may require a lock on some platforms.

   static char*      local_time_string(char *buf, size_t buflen);

   static struct tm* localtime_pd     (const time_t* clock, struct tm*  res);

   // Fill in buffer with current local time as an ISO-8601 string.

   // E.g., YYYY-MM-DDThh:mm:ss.mmm+zzzz.

   // Returns buffer, or NULL if it failed.

   static char* iso8601_time(char* buffer, size_t buffer_length);

   // Interface for detecting multiprocessor system

   static inline bool is_MP() {

     assert(_processor_count > 0, "invalid processor count");

     return _processor_count > 1;

   }

   static julong available_memory();

   static julong physical_memory();

   static julong allocatable_physical_memory(julong size);

   static bool is_server_class_machine();

   // number of CPUs

   static int processor_count() {

     return _processor_count;

   }

   static void set_processor_count(int count) { _processor_count = count; }

   // Returns the number of CPUs this process is currently allowed to run on.

   // Note that on some OSes this can change dynamically.

   static int active_processor_count();

   // Bind processes to processors.

   //     This is a two step procedure:

   //     first you generate a distribution of processes to processors,

   //     then you bind processes according to that distribution.

   // Compute a distribution for number of processes to processors.

   //    Stores the processor id's into the distribution array argument.

   //    Returns true if it worked, false if it didn't.

   static bool distribute_processes(uint length, uint* distribution);

   // Binds the current process to a processor.

   //    Returns true if it worked, false if it didn't.

   static bool bind_to_processor(uint processor_id);

   // Interface for stack banging (predetect possible stack overflow for

   // exception processing)  There are guard pages, and above that shadow

   // pages for stack overflow checking.

   static bool uses_stack_guard_pages();

   static bool allocate_stack_guard_pages();

   static void bang_stack_shadow_pages();

   static bool stack_shadow_pages_available(Thread *thread, methodHandle method);

   // OS interface to Virtual Memory

   // Return the default page size.

   static int    vm_page_size();

   // Return the page size to use for a region of memory.  The min_pages argument

   // is a hint intended to limit fragmentation; it says the returned page size

   // should be <= region_max_size / min_pages.  Because min_pages is a hint,

   // this routine may return a size larger than region_max_size / min_pages.

   //

   // The current implementation ignores min_pages if a larger page size is an

   // exact multiple of both region_min_size and region_max_size.  This allows

   // larger pages to be used when doing so would not cause fragmentation; in

   // particular, a single page can be used when region_min_size ==

   // region_max_size == a supported page size.

   static size_t page_size_for_region(size_t region_min_size,

                                      size_t region_max_size,

                                      uint min_pages);

   // Method for tracing page sizes returned by the above method; enabled by

   // TracePageSizes.  The region_{min,max}_size parameters should be the values

   // passed to page_size_for_region() and page_size should be the result of that

   // call.  The (optional) base and size parameters should come from the

   // ReservedSpace base() and size() methods.

   static void trace_page_sizes(const char* str, const size_t region_min_size,

                                const size_t region_max_size,

                                const size_t page_size,

                                const char* base = NULL,

                                const size_t size = 0) PRODUCT_RETURN;

   static int    vm_allocation_granularity();

   static char*  reserve_memory(size_t bytes, char* addr = 0,

                                size_t alignment_hint = 0);

   static char*  attempt_reserve_memory_at(size_t bytes, char* addr);

   static void   split_reserved_memory(char *base, size_t size,

                                       size_t split, bool realloc);

   static bool   commit_memory(char* addr, size_t bytes,

                               bool executable = false);

   static bool   commit_memory(char* addr, size_t size, size_t alignment_hint,

                               bool executable = false);

   static bool   uncommit_memory(char* addr, size_t bytes);

   static bool   release_memory(char* addr, size_t bytes);

   enum ProtType { MEM_PROT_NONE, MEM_PROT_READ, MEM_PROT_RW, MEM_PROT_RWX };

   static bool   protect_memory(char* addr, size_t bytes, ProtType prot,

                                bool is_committed = true);

   static bool   guard_memory(char* addr, size_t bytes);

   static bool   unguard_memory(char* addr, size_t bytes);

   static bool   create_stack_guard_pages(char* addr, size_t bytes);

   static bool   remove_stack_guard_pages(char* addr, size_t bytes);

   static char*  map_memory(int fd, const char* file_name, size_t file_offset,

                            char *addr, size_t bytes, bool read_only = false,

                            bool allow_exec = false);

   static char*  remap_memory(int fd, const char* file_name, size_t file_offset,

                              char *addr, size_t bytes, bool read_only,

                              bool allow_exec);

   static bool   unmap_memory(char *addr, size_t bytes);

   static void   free_memory(char *addr, size_t bytes);

   static void   realign_memory(char *addr, size_t bytes, size_t alignment_hint);

   // NUMA-specific interface

   static bool   numa_has_static_binding();

   static bool   numa_has_group_homing();

   static void   numa_make_local(char *addr, size_t bytes, int lgrp_hint);

   static void   numa_make_global(char *addr, size_t bytes);

   static size_t numa_get_groups_num();

   static size_t numa_get_leaf_groups(int *ids, size_t size);

   static bool   numa_topology_changed();

   static int    numa_get_group_id();

   // Page manipulation

   struct page_info {

     size_t size;

     int lgrp_id;

   };

   static bool   get_page_info(char *start, page_info* info);

   static char*  scan_pages(char *start, char* end, page_info* page_expected, page_info* page_found);

   static char*  non_memory_address_word();

   // reserve, commit and pin the entire memory region

   static char*  reserve_memory_special(size_t size, char* addr = NULL,

                 bool executable = false);

   static bool   release_memory_special(char* addr, size_t bytes);

   static void   large_page_init();

   static size_t large_page_size();

   static bool   can_commit_large_page_memory();

   static bool   can_execute_large_page_memory();

   // OS interface to polling page

   static address get_polling_page()             { return _polling_page; }

   static void    set_polling_page(address page) { _polling_page = page; }

   static bool    is_poll_address(address addr)  { return addr >= _polling_page && addr < (_polling_page + os::vm_page_size()); }

   static void    make_polling_page_unreadable();

   static void    make_polling_page_readable();

   // Routines used to serialize the thread state without using membars

   static void    serialize_thread_states();

   // Since we write to the serialize page from every thread, we

   // want stores to be on unique cache lines whenever possible

   // in order to minimize CPU cross talk.  We pre-compute the

   // amount to shift the thread* to make this offset unique to

   // each thread.

   static int     get_serialize_page_shift_count() {

     return SerializePageShiftCount;

   }

   static void     set_serialize_page_mask(uintptr_t mask) {

     _serialize_page_mask = mask;

   }

   static unsigned int  get_serialize_page_mask() {

     return _serialize_page_mask;

   }

   static void    set_memory_serialize_page(address page);

   static address get_memory_serialize_page() {

     return (address)_mem_serialize_page;

   }

   static inline void write_memory_serialize_page(JavaThread *thread) {

     uintptr_t page_offset = ((uintptr_t)thread >>

                             get_serialize_page_shift_count()) &

                             get_serialize_page_mask();

     *(volatile int32_t *)((uintptr_t)_mem_serialize_page+page_offset) = 1;

   }

   static bool    is_memory_serialize_page(JavaThread *thread, address addr) {

     if (UseMembar) return false;

     // Previously this function calculated the exact address of this

     // thread's serialize page, and checked if the faulting address

     // was equal.  However, some platforms mask off faulting addresses

     // to the page size, so now we just check that the address is

     // within the page.  This makes the thread argument unnecessary,

     // but we retain the NULL check to preserve existing behaviour.

     if (thread == NULL) return false;

     address page = (address) _mem_serialize_page;

     return addr >= page && addr < (page + os::vm_page_size());

   }

   static void block_on_serialize_page_trap();

   // threads

   enum ThreadType {

     vm_thread,

     cgc_thread,        // Concurrent GC thread

     pgc_thread,        // Parallel GC thread

     java_thread,

     compiler_thread,

     watcher_thread,

     os_thread

   };

   static bool create_thread(Thread* thread,

                             ThreadType thr_type,

                             size_t stack_size = 0);

   static bool create_main_thread(JavaThread* thread);

   static bool create_attached_thread(JavaThread* thread);

   static void pd_start_thread(Thread* thread);

   static void start_thread(Thread* thread);

   static void initialize_thread();

   static void free_thread(OSThread* osthread);

   // thread id on Linux/64bit is 64bit, on Windows and Solaris, it's 32bit

   static intx current_thread_id();

   static int current_process_id();

   static int sleep(Thread* thread, jlong ms, bool interruptable);

   static int naked_sleep();

   static void infinite_sleep(); // never returns, use with CAUTION

   static void yield();        // Yields to all threads with same priority

   enum YieldResult {

     YIELD_SWITCHED = 1,         // caller descheduled, other ready threads exist & ran

     YIELD_NONEREADY = 0,        // No other runnable/ready threads.

                                 // platform-specific yield return immediately

     YIELD_UNKNOWN = -1          // Unknown: platform doesn't support _SWITCHED or _NONEREADY

     // YIELD_SWITCHED and YIELD_NONREADY imply the platform supports a "strong"

     // yield that can be used in lieu of blocking.

   } ;

   static YieldResult NakedYield () ;

   static void yield_all(int attempts = 0); // Yields to all other threads including lower priority

   static void loop_breaker(int attempts);  // called from within tight loops to possibly influence time-sharing

   static OSReturn set_priority(Thread* thread, ThreadPriority priority);

   static OSReturn get_priority(const Thread* const thread, ThreadPriority& priority);

   static void interrupt(Thread* thread);

   static bool is_interrupted(Thread* thread, bool clear_interrupted);

   static int pd_self_suspend_thread(Thread* thread);

   static ExtendedPC fetch_frame_from_context(void* ucVoid, intptr_t** sp, intptr_t** fp);

   static frame      fetch_frame_from_context(void* ucVoid);

   static ExtendedPC get_thread_pc(Thread *thread);

   static void breakpoint();

   static address current_stack_pointer();

   static address current_stack_base();

   static size_t current_stack_size();

   static int message_box(const char* title, const char* message);

   static char* do_you_want_to_debug(const char* message);

   // run cmd in a separate process and return its exit code; or -1 on failures

   static int fork_and_exec(char *cmd);

   // Set file to send error reports.

   static void set_error_file(const char *logfile);

   // os::exit() is merged with vm_exit()

   // static void exit(int num);

   // Terminate the VM, but don't exit the process

   static void shutdown();

   // Terminate with an error.  Default is to generate a core file on platforms

   // that support such things.  This calls shutdown() and then aborts.

   static void abort(bool dump_core = true);

   // Die immediately, no exit hook, no abort hook, no cleanup.

   static void die();

   // File i/o operations

   static const int default_file_open_flags();

   static int open(const char *path, int oflag, int mode);

   static int close(int fd);

   static jlong lseek(int fd, jlong offset, int whence);

   static char* native_path(char *path);

   static int ftruncate(int fd, jlong length);

   static int fsync(int fd);

   static int available(int fd, jlong *bytes);

   //File i/o operations

   static size_t read(int fd, void *buf, unsigned int nBytes);

   static size_t restartable_read(int fd, void *buf, unsigned int nBytes);

   static size_t write(int fd, const void *buf, unsigned int nBytes);

   // Reading directories.

   static DIR*           opendir(const char* dirname);

   static int            readdir_buf_size(const char *path);

   static struct dirent* readdir(DIR* dirp, dirent* dbuf);

   static int            closedir(DIR* dirp);

   // Dynamic library extension

   static const char*    dll_file_extension();

   static const char*    get_temp_directory();

   static const char*    get_current_directory(char *buf, int buflen);

   // Builds a platform-specific full library path given a ld path and lib name

   static void           dll_build_name(char* buffer, size_t size,

                                        const char* pathname, const char* fname);

   // Symbol lookup, find nearest function name; basically it implements

   // dladdr() for all platforms. Name of the nearest function is copied

   // to buf. Distance from its base address is returned as offset.

   // If function name is not found, buf[0] is set to '\0' and offset is

   // set to -1.

   static bool dll_address_to_function_name(address addr, char* buf,

                                            int buflen, int* offset);

   // Locate DLL/DSO. On success, full path of the library is copied to

   // buf, and offset is set to be the distance between addr and the

   // library's base address. On failure, buf[0] is set to '\0' and

   // offset is set to -1.

   static bool dll_address_to_library_name(address addr, char* buf,

                                           int buflen, int* offset);

   // Find out whether the pc is in the static code for jvm.dll/libjvm.so.

   static bool address_is_in_vm(address addr);

   // Loads .dll/.so and

   // in case of error it checks if .dll/.so was built for the

   // same architecture as Hotspot is running on

   static void* dll_load(const char *name, char *ebuf, int ebuflen);

   // lookup symbol in a shared library

   static void* dll_lookup(void* handle, const char* name);

   // Unload library

   static void  dll_unload(void *lib);

   // Print out system information; they are called by fatal error handler.

   // Output format may be different on different platforms.

   static void print_os_info(outputStream* st);

   static void print_cpu_info(outputStream* st);

   static void print_memory_info(outputStream* st);

   static void print_dll_info(outputStream* st);

   static void print_environment_variables(outputStream* st, const char** env_list, char* buffer, int len);

   static void print_context(outputStream* st, void* context);

   static void print_register_info(outputStream* st, void* context);

   static void print_siginfo(outputStream* st, void* siginfo);

   static void print_signal_handlers(outputStream* st, char* buf, size_t buflen);

   static void print_date_and_time(outputStream* st);

   static void print_location(outputStream* st, intptr_t x, bool verbose = false);

   static size_t lasterror(char *buf, size_t len);

   // Determines whether the calling process is being debugged by a user-mode debugger.

   static bool is_debugger_attached();

   // wait for a key press if PauseAtExit is set

   static void wait_for_keypress_at_exit(void);

   // The following two functions are used by fatal error handler to trace

   // native (C) frames. They are not part of frame.hpp/frame.cpp because

   // frame.hpp/cpp assume thread is JavaThread, and also because different

   // OS/compiler may have different convention or provide different API to

   // walk C frames.

   //

   // We don't attempt to become a debugger, so we only follow frames if that

   // does not require a lookup in the unwind table, which is part of the binary

   // file but may be unsafe to read after a fatal error. So on x86, we can

   // only walk stack if %ebp is used as frame pointer; on ia64, it's not

   // possible to walk C stack without having the unwind table.

   static bool is_first_C_frame(frame *fr);

   static frame get_sender_for_C_frame(frame *fr);

   // return current frame. pc() and sp() are set to NULL on failure.

   static frame      current_frame();

   static void print_hex_dump(outputStream* st, address start, address end, int unitsize);

   // returns a string to describe the exception/signal;

   // returns NULL if exception_code is not an OS exception/signal.

   static const char* exception_name(int exception_code, char* buf, size_t buflen);

   // Returns native Java library, loads if necessary

   static void*    native_java_library();

   // Fills in path to jvm.dll/libjvm.so (used by the Disassembler)

   static void     jvm_path(char *buf, jint buflen);

   // Returns true if we are running in a headless jre.

   static bool     is_headless_jre();

   // JNI names

   static void     print_jni_name_prefix_on(outputStream* st, int args_size);

   static void     print_jni_name_suffix_on(outputStream* st, int args_size);

   // File conventions

   static const char* file_separator();

   static const char* line_separator();

   static const char* path_separator();

   // Init os specific system properties values

   static void init_system_properties_values();

   // IO operations, non-JVM_ version.

   static int stat(const char* path, struct stat* sbuf);

   static bool dir_is_empty(const char* path);

   // IO operations on binary files

   static int create_binary_file(const char* path, bool rewrite_existing);

   static jlong current_file_offset(int fd);

   static jlong seek_to_file_offset(int fd, jlong offset);

   // Thread Local Storage

   static int   allocate_thread_local_storage();

   static void  thread_local_storage_at_put(int index, void* value);

   static void* thread_local_storage_at(int index);

   static void  free_thread_local_storage(int index);

   // General allocation (must be MT-safe)

   static void* malloc  (size_t size);

   static void* realloc (void *memblock, size_t size);

   static void  free    (void *memblock);

   static bool  check_heap(bool force = false);      // verify C heap integrity

   static char* strdup(const char *);  // Like strdup

 #ifndef PRODUCT

   static julong num_mallocs;         // # of calls to malloc/realloc

   static julong alloc_bytes;         // # of bytes allocated

   static julong num_frees;           // # of calls to free

   static julong free_bytes;          // # of bytes freed

 #endif

   // SocketInterface (ex HPI SocketInterface )

   static int socket(int domain, int type, int protocol);

   static int socket_close(int fd);

   static int socket_shutdown(int fd, int howto);

   static int recv(int fd, char *buf, int nBytes, int flags);

   static int send(int fd, char *buf, int nBytes, int flags);

   static int raw_send(int fd, char *buf, int nBytes, int flags);

   static int timeout(int fd, long timeout);

   static int listen(int fd, int count);

   static int connect(int fd, struct sockaddr *him, int len);

   static int bind(int fd, struct sockaddr *him, int len);

   static int accept(int fd, struct sockaddr *him, int *len);

   static int recvfrom(int fd, char *buf, int nbytes, int flags,

                              struct sockaddr *from, int *fromlen);

   static int get_sock_name(int fd, struct sockaddr *him, int *len);

   static int sendto(int fd, char *buf, int len, int flags,

                            struct sockaddr *to, int tolen);

   static int socket_available(int fd, jint *pbytes);

   static int get_sock_opt(int fd, int level, int optname,

                            char *optval, int* optlen);

   static int set_sock_opt(int fd, int level, int optname,

                            const char *optval, int optlen);

   static int get_host_name(char* name, int namelen);

   static struct hostent*  get_host_by_name(char* name);

   // Printing 64 bit integers

   static const char* jlong_format_specifier();

   static const char* julong_format_specifier();

   // Support for signals (see JVM_RaiseSignal, JVM_RegisterSignal)

   static void  signal_init();

   static void  signal_init_pd();

   static void  signal_notify(int signal_number);

   static void* signal(int signal_number, void* handler);

   static void  signal_raise(int signal_number);

   static int   signal_wait();

   static int   signal_lookup();

   static void* user_handler();

   static void  terminate_signal_thread();

   static int   sigexitnum_pd();

   // random number generation

   static long random();                    // return 32bit pseudorandom number

   static void init_random(long initval);   // initialize random sequence

   // Structured OS Exception support

   static void os_exception_wrapper(java_call_t f, JavaValue* value, methodHandle* method, JavaCallArguments* args, Thread* thread);

   // On Windows this will create an actual minidump, on Linux/Solaris it will simply check core dump limits

   static void check_or_create_dump(void* exceptionRecord, void* contextRecord, char* buffer, size_t bufferSize);

   // JVMTI & JVM monitoring and management support

   // The thread_cpu_time() and current_thread_cpu_time() are only

   // supported if is_thread_cpu_time_supported() returns true.

   // They are not supported on Solaris T1.

   // Thread CPU Time - return the fast estimate on a platform

   // On Solaris - call gethrvtime (fast) - user time only

   // On Linux   - fast clock_gettime where available - user+sys

   //            - otherwise: very slow /proc fs - user+sys

   // On Windows - GetThreadTimes - user+sys

   static jlong current_thread_cpu_time();

   static jlong thread_cpu_time(Thread* t);

   // Thread CPU Time with user_sys_cpu_time parameter.

   //

   // If user_sys_cpu_time is true, user+sys time is returned.

   // Otherwise, only user time is returned

   static jlong current_thread_cpu_time(bool user_sys_cpu_time);

   static jlong thread_cpu_time(Thread* t, bool user_sys_cpu_time);

   // Return a bunch of info about the timers.

   // Note that the returned info for these two functions may be different

   // on some platforms

   static void current_thread_cpu_time_info(jvmtiTimerInfo *info_ptr);

   static void thread_cpu_time_info(jvmtiTimerInfo *info_ptr);

   static bool is_thread_cpu_time_supported();

   // System loadavg support.  Returns -1 if load average cannot be obtained.

   static int loadavg(double loadavg[], int nelem);

   // Hook for os specific jvm options that we don't want to abort on seeing

   static bool obsolete_option(const JavaVMOption *option);

   // Read file line by line. If line is longer than bsize,

   // rest of line is skipped. Returns number of bytes read or -1 on EOF

   static int get_line_chars(int fd, char *buf, const size_t bsize);

   // Platform dependent stuff

 #ifdef TARGET_OS_FAMILY_linux

 # include "os_linux.hpp"

 #endif

 #ifdef TARGET_OS_FAMILY_solaris

 # include "os_solaris.hpp"

 #endif

 #ifdef TARGET_OS_FAMILY_windows

 # include "os_windows.hpp"

 #endif

 #ifdef TARGET_OS_ARCH_linux_x86

 # include "os_linux_x86.hpp"

 #endif

 #ifdef TARGET_OS_ARCH_linux_sparc

 # include "os_linux_sparc.hpp"

 #endif

 #ifdef TARGET_OS_ARCH_linux_zero

 # include "os_linux_zero.hpp"

 #endif

 #ifdef TARGET_OS_ARCH_solaris_x86

 # include "os_solaris_x86.hpp"

 #endif

 #ifdef TARGET_OS_ARCH_solaris_sparc

 # include "os_solaris_sparc.hpp"

 #endif

 #ifdef TARGET_OS_ARCH_windows_x86

 # include "os_windows_x86.hpp"

 #endif

 #ifdef TARGET_OS_ARCH_linux_arm

 # include "os_linux_arm.hpp"

 #endif

 #ifdef TARGET_OS_ARCH_linux_ppc

 # include "os_linux_ppc.hpp"

 #endif

   // debugging support (mostly used by debug.cpp but also fatal error handler)

   static bool find(address pc, outputStream* st = tty); // OS specific function to make sense out of an address

   static bool dont_yield();                     // when true, JVM_Yield() is nop

   static void print_statistics();

   // Thread priority helpers (implemented in OS-specific part)

   static OSReturn set_native_priority(Thread* thread, int native_prio);

   static OSReturn get_native_priority(const Thread* const thread, int* priority_ptr);

   static int java_to_os_priority[MaxPriority + 1];

   // Hint to the underlying OS that a task switch would not be good.

   // Void return because it's a hint and can fail.

   static void hint_no_preempt();

   // Used at creation if requested by the diagnostic flag PauseAtStartup.

   // Causes the VM to wait until an external stimulus has been applied

   // (for Unix, that stimulus is a signal, for Windows, an external

   // ResumeThread call)

   static void pause();

  protected:

   static long _rand_seed;                   // seed for random number generator

   static int _processor_count;              // number of processors

   static char* format_boot_path(const char* format_string,

                                 const char* home,

                                 int home_len,

                                 char fileSep,

                                 char pathSep);

   static bool set_boot_path(char fileSep, char pathSep);

   static char** split_path(const char* path, int* n);

 };

 // Note that "PAUSE" is almost always used with synchronization

 // so arguably we should provide Atomic::SpinPause() instead

 // of the global SpinPause() with C linkage.

 // It'd also be eligible for inlining on many platforms.

 extern "C" int SpinPause () ;

 extern "C" int SafeFetch32 (int * adr, int errValue) ;

 extern "C" intptr_t SafeFetchN (intptr_t * adr, intptr_t errValue) ;

 #endif // SHARE_VM_RUNTIME_OS_HPP