third_party/tcmalloc/vendor/src/maybe_threads.cc

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  29
  30 // ---
  31 // Author: Paul Menage <opensource@google.com>
  32 //
  33 // Some wrappers for pthread functions so that we can be LD_PRELOADed
  34 // against non-pthreads apps.
  35 //
  36 // This module will behave very strangely if some pthreads functions
  37 // exist and others don't.
  38
  39 #include "config.h"
  40 #include <assert.h>
  41 #include <string.h>    // for memcmp
  42 #include <stdio.h>     // for __isthreaded on FreeBSD
  43 // We don't actually need strings. But including this header seems to
  44 // stop the compiler trying to short-circuit our pthreads existence
  45 // tests and claiming that the address of a function is always
  46 // non-zero. I have no idea why ...
  47 #include <string>
  48 #include "maybe_threads.h"
  49 #include "base/basictypes.h"
  50
  51 // __THROW is defined in glibc systems.  It means, counter-intuitively,
  52 // "This function will never throw an exception."  It's an optional
  53 // optimization tool, but we may need to use it to match glibc prototypes.
  54 #ifndef __THROW    // I guess we're not on a glibc system
  55 # define __THROW   // __THROW is just an optimization, so ok to make it ""
  56 #endif
  57
  58 // These are the methods we're going to conditionally include.
  59 extern "C" {
  60   int pthread_key_create (pthread_key_t*, void (*)(void*))
  61       __THROW ATTRIBUTE_WEAK;
  62   void *pthread_getspecific(pthread_key_t)
  63       __THROW ATTRIBUTE_WEAK;
  64   int pthread_setspecific(pthread_key_t, const void*)
  65       __THROW ATTRIBUTE_WEAK;
  66   int pthread_once(pthread_once_t *, void (*)(void))
  67       ATTRIBUTE_WEAK;
  68 }
  69
  70 #define MAX_PERTHREAD_VALS 16
  71 static void *perftools_pthread_specific_vals[MAX_PERTHREAD_VALS];
  72 static int next_key;
  73
  74 int perftools_pthread_key_create(pthread_key_t *key,
  75                                  void (*destr_function) (void *)) {
  76   if (pthread_key_create) {
  77     return pthread_key_create(key, destr_function);
  78   } else {
  79     assert(next_key < MAX_PERTHREAD_VALS);
  80     *key = (pthread_key_t)(next_key++);
  81     return 0;
  82   }
  83 }
  84
  85 void *perftools_pthread_getspecific(pthread_key_t key) {
  86   if (pthread_getspecific) {
  87     return pthread_getspecific(key);
  88   } else {
  89     return perftools_pthread_specific_vals[(int)key];
  90   }
  91 }
  92
  93 int perftools_pthread_setspecific(pthread_key_t key, void *val) {
  94   if (pthread_setspecific) {
  95     return pthread_setspecific(key, val);
  96   } else {
  97     perftools_pthread_specific_vals[(int)key] = val;
  98     return 0;
  99   }
 100 }
 101
 102
 103 static pthread_once_t pthread_once_init = PTHREAD_ONCE_INIT;
 104 int perftools_pthread_once(pthread_once_t *ctl,
 105                            void  (*init_routine) (void)) {
 106 #ifdef __FreeBSD__
 107   // On __FreeBSD__, calling pthread_once on a system that is not
 108   // linked with -pthread is silently a noop. :-( Luckily, we have a
 109   // workaround: FreeBSD exposes __isthreaded in <stdio.h>, which is
 110   // set to 1 when the first thread is spawned.  So on those systems,
 111   // we can use our own separate pthreads-once mechanism, which is
 112   // used until __isthreaded is 1 (which will never be true if the app
 113   // is not linked with -pthread).
 114   static bool pthread_once_ran_before_threads = false;
 115   if (pthread_once_ran_before_threads) {
 116     return 0;
 117   }
 118   if (!__isthreaded) {
 119     init_routine();
 120     pthread_once_ran_before_threads = true;
 121     return 0;
 122   }
 123 #endif
 124   if (pthread_once) {
 125     return pthread_once(ctl, init_routine);
 126   } else {
 127     if (memcmp(ctl, &pthread_once_init, sizeof(*ctl)) == 0) {
 128       init_routine();
 129       ++*(char*)(ctl);        // make it so it's no longer equal to init
 130     }
 131     return 0;
 132   }
 133 }