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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "base/threading/platform_thread.h"
      6 
      7 #import <Foundation/Foundation.h>
      8 #include <algorithm>
      9 #include <dlfcn.h>
     10 #include <mach/mach.h>
     11 #include <mach/mach_time.h>
     12 #include <mach/thread_policy.h>
     13 #include <sys/resource.h>
     14 
     15 #include "base/lazy_instance.h"
     16 #include "base/logging.h"
     17 #include "base/threading/thread_id_name_manager.h"
     18 #include "base/tracked_objects.h"
     19 
     20 namespace base {
     21 
     22 // If Cocoa is to be used on more than one thread, it must know that the
     23 // application is multithreaded.  Since it's possible to enter Cocoa code
     24 // from threads created by pthread_thread_create, Cocoa won't necessarily
     25 // be aware that the application is multithreaded.  Spawning an NSThread is
     26 // enough to get Cocoa to set up for multithreaded operation, so this is done
     27 // if necessary before pthread_thread_create spawns any threads.
     28 //
     29 // http://developer.apple.com/documentation/Cocoa/Conceptual/Multithreading/CreatingThreads/chapter_4_section_4.html
     30 void InitThreading() {
     31   static BOOL multithreaded = [NSThread isMultiThreaded];
     32   if (!multithreaded) {
     33     // +[NSObject class] is idempotent.
     34     [NSThread detachNewThreadSelector:@selector(class)
     35                              toTarget:[NSObject class]
     36                            withObject:nil];
     37     multithreaded = YES;
     38 
     39     DCHECK([NSThread isMultiThreaded]);
     40   }
     41 }
     42 
     43 // static
     44 void PlatformThread::SetName(const char* name) {
     45   ThreadIdNameManager::GetInstance()->SetName(CurrentId(), name);
     46   tracked_objects::ThreadData::InitializeThreadContext(name);
     47 
     48   // pthread_setname_np is only available in 10.6 or later, so test
     49   // for it at runtime.
     50   int (*dynamic_pthread_setname_np)(const char*);
     51   *reinterpret_cast<void**>(&dynamic_pthread_setname_np) =
     52       dlsym(RTLD_DEFAULT, "pthread_setname_np");
     53   if (!dynamic_pthread_setname_np)
     54     return;
     55 
     56   // Mac OS X does not expose the length limit of the name, so
     57   // hardcode it.
     58   const int kMaxNameLength = 63;
     59   std::string shortened_name = std::string(name).substr(0, kMaxNameLength);
     60   // pthread_setname() fails (harmlessly) in the sandbox, ignore when it does.
     61   // See http://crbug.com/47058
     62   dynamic_pthread_setname_np(shortened_name.c_str());
     63 }
     64 
     65 namespace {
     66 
     67 void SetPriorityNormal(mach_port_t mach_thread_id) {
     68   // Make thread standard policy.
     69   // Please note that this call could fail in rare cases depending
     70   // on runtime conditions.
     71   thread_standard_policy policy;
     72   kern_return_t result = thread_policy_set(mach_thread_id,
     73                                            THREAD_STANDARD_POLICY,
     74                                            (thread_policy_t)&policy,
     75                                            THREAD_STANDARD_POLICY_COUNT);
     76 
     77   if (result != KERN_SUCCESS)
     78     DVLOG(1) << "thread_policy_set() failure: " << result;
     79 }
     80 
     81 // Enables time-contraint policy and priority suitable for low-latency,
     82 // glitch-resistant audio.
     83 void SetPriorityRealtimeAudio(mach_port_t mach_thread_id) {
     84   kern_return_t result;
     85 
     86   // Increase thread priority to real-time.
     87 
     88   // Please note that the thread_policy_set() calls may fail in
     89   // rare cases if the kernel decides the system is under heavy load
     90   // and is unable to handle boosting the thread priority.
     91   // In these cases we just return early and go on with life.
     92 
     93   // Make thread fixed priority.
     94   thread_extended_policy_data_t policy;
     95   policy.timeshare = 0;  // Set to 1 for a non-fixed thread.
     96   result = thread_policy_set(mach_thread_id,
     97                              THREAD_EXTENDED_POLICY,
     98                              (thread_policy_t)&policy,
     99                              THREAD_EXTENDED_POLICY_COUNT);
    100   if (result != KERN_SUCCESS) {
    101     DVLOG(1) << "thread_policy_set() failure: " << result;
    102     return;
    103   }
    104 
    105   // Set to relatively high priority.
    106   thread_precedence_policy_data_t precedence;
    107   precedence.importance = 63;
    108   result = thread_policy_set(mach_thread_id,
    109                              THREAD_PRECEDENCE_POLICY,
    110                              (thread_policy_t)&precedence,
    111                              THREAD_PRECEDENCE_POLICY_COUNT);
    112   if (result != KERN_SUCCESS) {
    113     DVLOG(1) << "thread_policy_set() failure: " << result;
    114     return;
    115   }
    116 
    117   // Most important, set real-time constraints.
    118 
    119   // Define the guaranteed and max fraction of time for the audio thread.
    120   // These "duty cycle" values can range from 0 to 1.  A value of 0.5
    121   // means the scheduler would give half the time to the thread.
    122   // These values have empirically been found to yield good behavior.
    123   // Good means that audio performance is high and other threads won't starve.
    124   const double kGuaranteedAudioDutyCycle = 0.75;
    125   const double kMaxAudioDutyCycle = 0.85;
    126 
    127   // Define constants determining how much time the audio thread can
    128   // use in a given time quantum.  All times are in milliseconds.
    129 
    130   // About 128 frames @44.1KHz
    131   const double kTimeQuantum = 2.9;
    132 
    133   // Time guaranteed each quantum.
    134   const double kAudioTimeNeeded = kGuaranteedAudioDutyCycle * kTimeQuantum;
    135 
    136   // Maximum time each quantum.
    137   const double kMaxTimeAllowed = kMaxAudioDutyCycle * kTimeQuantum;
    138 
    139   // Get the conversion factor from milliseconds to absolute time
    140   // which is what the time-constraints call needs.
    141   mach_timebase_info_data_t tb_info;
    142   mach_timebase_info(&tb_info);
    143   double ms_to_abs_time =
    144       ((double)tb_info.denom / (double)tb_info.numer) * 1000000;
    145 
    146   thread_time_constraint_policy_data_t time_constraints;
    147   time_constraints.period = kTimeQuantum * ms_to_abs_time;
    148   time_constraints.computation = kAudioTimeNeeded * ms_to_abs_time;
    149   time_constraints.constraint = kMaxTimeAllowed * ms_to_abs_time;
    150   time_constraints.preemptible = 0;
    151 
    152   result = thread_policy_set(mach_thread_id,
    153                              THREAD_TIME_CONSTRAINT_POLICY,
    154                              (thread_policy_t)&time_constraints,
    155                              THREAD_TIME_CONSTRAINT_POLICY_COUNT);
    156   if (result != KERN_SUCCESS)
    157     DVLOG(1) << "thread_policy_set() failure: " << result;
    158 
    159   return;
    160 }
    161 
    162 }  // anonymous namespace
    163 
    164 // static
    165 void PlatformThread::SetThreadPriority(PlatformThreadHandle handle,
    166                                        ThreadPriority priority) {
    167   // Convert from pthread_t to mach thread identifier.
    168   mach_port_t mach_thread_id = pthread_mach_thread_np(handle.handle_);
    169 
    170   switch (priority) {
    171     case kThreadPriority_Normal:
    172       SetPriorityNormal(mach_thread_id);
    173       break;
    174     case kThreadPriority_RealtimeAudio:
    175       SetPriorityRealtimeAudio(mach_thread_id);
    176       break;
    177     default:
    178       NOTREACHED() << "Unknown priority.";
    179       break;
    180   }
    181 }
    182 
    183 size_t GetDefaultThreadStackSize(const pthread_attr_t& attributes) {
    184 #if defined(OS_IOS)
    185   return 0;
    186 #else
    187   // The Mac OS X default for a pthread stack size is 512kB.
    188   // Libc-594.1.4/pthreads/pthread.c's pthread_attr_init uses
    189   // DEFAULT_STACK_SIZE for this purpose.
    190   //
    191   // 512kB isn't quite generous enough for some deeply recursive threads that
    192   // otherwise request the default stack size by specifying 0. Here, adopt
    193   // glibc's behavior as on Linux, which is to use the current stack size
    194   // limit (ulimit -s) as the default stack size. See
    195   // glibc-2.11.1/nptl/nptl-init.c's __pthread_initialize_minimal_internal. To
    196   // avoid setting the limit below the Mac OS X default or the minimum usable
    197   // stack size, these values are also considered. If any of these values
    198   // can't be determined, or if stack size is unlimited (ulimit -s unlimited),
    199   // stack_size is left at 0 to get the system default.
    200   //
    201   // Mac OS X normally only applies ulimit -s to the main thread stack. On
    202   // contemporary OS X and Linux systems alike, this value is generally 8MB
    203   // or in that neighborhood.
    204   size_t default_stack_size = 0;
    205   struct rlimit stack_rlimit;
    206   if (pthread_attr_getstacksize(&attributes, &default_stack_size) == 0 &&
    207       getrlimit(RLIMIT_STACK, &stack_rlimit) == 0 &&
    208       stack_rlimit.rlim_cur != RLIM_INFINITY) {
    209     default_stack_size =
    210         std::max(std::max(default_stack_size,
    211                           static_cast<size_t>(PTHREAD_STACK_MIN)),
    212                  static_cast<size_t>(stack_rlimit.rlim_cur));
    213   }
    214   return default_stack_size;
    215 #endif
    216 }
    217 
    218 void InitOnThread() {
    219 }
    220 
    221 void TerminateOnThread() {
    222 }
    223 
    224 }  // namespace base
    225