mono/utils/mono-lazy-init.h

   1 /**
   2  * \file
   3  * Lazy initialization and cleanup utilities
   4  *
   5  * Authors: Ludovic Henry <ludovic@xamarin.com>
   6  *
   7  * Copyright 2015 Xamarin, Inc. (www.xamarin.com)
   8  * Licensed under the MIT license. See LICENSE file in the project root for full license information.
   9  */
  10
  11 #ifndef __MONO_LAZY_INIT_H__
  12 #define __MONO_LAZY_INIT_H__
  13
  14 #include <glib.h>
  15
  16 #include <config.h>
  17
  18 #include "atomic.h"
  19 #include "mono-threads.h"
  20 #include "mono-memory-model.h"
  21
  22 /*
  23  * These functions should be used if you want some form of lazy initialization. You can have a look at the
  24  * threadpool for a more detailed example.
  25  *
  26  * The idea is that a module can be in 5 different states:
  27  *  - not initialized: it is the first state it starts in
  28  *  - initializing/initialized: whenever we need this module for the first time, we need to initialize it: allocate
  29  *     memory, launch background thread, etc. To achieve this, we have a module specific function (let's call it
  30  *     initialize)
  31  *  - cleaning/cleaned: when we want to clean this module specific data up, then we need to clean it up: deallocate
  32  *     memory, wait for background threads to finish, etc. As for the initialization process, we need a module specific
  33  *     function (let's call it cleanup)
  34  *
  35  * The switch from one state to the other can only happen in the following ways:
  36  *  - not initialized
  37  *  - not initialized -> initializing -> initialized
  38  *  - not initialized -> cleaned
  39  *  - not initialized -> initializing -> initialized -> cleaning -> cleaned
  40  *
  41  * The initialize and cleanup functions are guaranteed to:
  42  *  - be each called once and only once
  43  *  - not be called concurrently (either 2+ initialize or 2+ cleanup, either initialize and cleanup)
  44  */
  45
  46 typedef gint32 mono_lazy_init_t;
  47
  48 enum {
  49         MONO_LAZY_INIT_STATUS_NOT_INITIALIZED,
  50         MONO_LAZY_INIT_STATUS_INITIALIZING,
  51         MONO_LAZY_INIT_STATUS_INITIALIZED,
  52         MONO_LAZY_INIT_STATUS_CLEANING,
  53         MONO_LAZY_INIT_STATUS_CLEANED,
  54 };
  55
  56 static inline gboolean
  57 mono_lazy_initialize (mono_lazy_init_t *lazy_init, void (*initialize) (void))
  58 {
  59         gint32 status;
  60
  61         g_assert (lazy_init);
  62
  63         status = *lazy_init;
  64
  65         if (status >= MONO_LAZY_INIT_STATUS_INITIALIZED)
  66                 return status == MONO_LAZY_INIT_STATUS_INITIALIZED;
  67         if (status == MONO_LAZY_INIT_STATUS_INITIALIZING
  68              || mono_atomic_cas_i32 (lazy_init, MONO_LAZY_INIT_STATUS_INITIALIZING, MONO_LAZY_INIT_STATUS_NOT_INITIALIZED)
  69                  != MONO_LAZY_INIT_STATUS_NOT_INITIALIZED
  70         ) {
  71                 while (*lazy_init == MONO_LAZY_INIT_STATUS_INITIALIZING)
  72                         mono_thread_info_yield ();
  73                 g_assert (mono_atomic_load_i32 (lazy_init) >= MONO_LAZY_INIT_STATUS_INITIALIZED);
  74                 return status == MONO_LAZY_INIT_STATUS_INITIALIZED;
  75         }
  76
  77         initialize ();
  78
  79         mono_atomic_store_release (lazy_init, MONO_LAZY_INIT_STATUS_INITIALIZED);
  80         return TRUE;
  81 }
  82
  83 static inline void
  84 mono_lazy_cleanup (mono_lazy_init_t *lazy_init, void (*cleanup) (void))
  85 {
  86         gint32 status;
  87
  88         g_assert (lazy_init);
  89
  90         status = *lazy_init;
  91
  92         if (status == MONO_LAZY_INIT_STATUS_NOT_INITIALIZED
  93              && mono_atomic_cas_i32 (lazy_init, MONO_LAZY_INIT_STATUS_CLEANED, MONO_LAZY_INIT_STATUS_NOT_INITIALIZED)
  94                  == MONO_LAZY_INIT_STATUS_NOT_INITIALIZED
  95         ) {
  96                 return;
  97         }
  98         if (status == MONO_LAZY_INIT_STATUS_INITIALIZING) {
  99                 while ((status = *lazy_init) == MONO_LAZY_INIT_STATUS_INITIALIZING)
 100                         mono_thread_info_yield ();
 101         }
 102
 103         if (status == MONO_LAZY_INIT_STATUS_CLEANED)
 104                 return;
 105         if (status == MONO_LAZY_INIT_STATUS_CLEANING
 106              || mono_atomic_cas_i32 (lazy_init, MONO_LAZY_INIT_STATUS_CLEANING, MONO_LAZY_INIT_STATUS_INITIALIZED)
 107                  != MONO_LAZY_INIT_STATUS_INITIALIZED
 108         ) {
 109                 while (*lazy_init == MONO_LAZY_INIT_STATUS_CLEANING)
 110                         mono_thread_info_yield ();
 111                 g_assert (mono_atomic_load_i32 (lazy_init) == MONO_LAZY_INIT_STATUS_CLEANED);
 112                 return;
 113         }
 114
 115         cleanup ();
 116
 117         mono_atomic_store_release (lazy_init, MONO_LAZY_INIT_STATUS_CLEANED);
 118 }
 119
 120 static inline gboolean
 121 mono_lazy_is_initialized (mono_lazy_init_t *lazy_init)
 122 {
 123         g_assert (lazy_init);
 124         return mono_atomic_load_i32 (lazy_init) == MONO_LAZY_INIT_STATUS_INITIALIZED;
 125 }
 126
 127 #endif