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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
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4 -- --
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5 -- SYSTEM.TASKING.PROTECTED_OBJECTS.OPERATIONS --
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6 -- --
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7 -- S p e c --
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8 -- --
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145
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9 -- Copyright (C) 1992-2019, Free Software Foundation, Inc. --
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111
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10 -- --
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11 -- GNARL is free software; you can redistribute it and/or modify it under --
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12 -- terms of the GNU General Public License as published by the Free Soft- --
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13 -- ware Foundation; either version 3, or (at your option) any later ver- --
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14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
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17 -- --
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18 -- As a special exception under Section 7 of GPL version 3, you are granted --
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19 -- additional permissions described in the GCC Runtime Library Exception, --
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20 -- version 3.1, as published by the Free Software Foundation. --
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21 -- --
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22 -- You should have received a copy of the GNU General Public License and --
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23 -- a copy of the GCC Runtime Library Exception along with this program; --
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24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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25 -- <http://www.gnu.org/licenses/>. --
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26 -- --
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27 -- GNARL was developed by the GNARL team at Florida State University. --
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28 -- Extensive contributions were provided by Ada Core Technologies, Inc. --
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29 -- --
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30 ------------------------------------------------------------------------------
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31
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32 -- This package contains all the extended primitives related to protected
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33 -- objects with entries.
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34
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35 -- The handling of protected objects with no entries is done in
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36 -- System.Tasking.Protected_Objects, the simple routines for protected
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37 -- objects with entries in System.Tasking.Protected_Objects.Entries. The
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38 -- split between Entries and Operations is needed to break circular
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39 -- dependencies inside the run time.
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40
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41 -- Note: the compiler generates direct calls to this interface, via Rtsfind.
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42 -- Any changes to this interface may require corresponding compiler changes.
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43
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44 with Ada.Exceptions;
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45
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46 with System.Tasking.Protected_Objects.Entries;
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47
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48 package System.Tasking.Protected_Objects.Operations is
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49 pragma Elaborate_Body;
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50
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51 type Communication_Block is private;
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52 -- Objects of this type are passed between GNARL calls to allow RTS
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53 -- information to be preserved.
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54
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55 procedure Protected_Entry_Call
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56 (Object : Entries.Protection_Entries_Access;
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57 E : Protected_Entry_Index;
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58 Uninterpreted_Data : System.Address;
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59 Mode : Call_Modes;
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60 Block : out Communication_Block);
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61 -- Make a protected entry call to the specified object.
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62 -- Pend a protected entry call on the protected object represented
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63 -- by Object. A pended call is not queued; it may be executed immediately
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64 -- or queued, depending on the state of the entry barrier.
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65 --
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66 -- E
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67 -- The index representing the entry to be called.
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68 --
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69 -- Uninterpreted_Data
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70 -- This will be returned by Next_Entry_Call when this call is serviced.
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71 -- It can be used by the compiler to pass information between the
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72 -- caller and the server, in particular entry parameters.
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73 --
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74 -- Mode
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75 -- The kind of call to be pended
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76 --
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77 -- Block
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78 -- Information passed between runtime calls by the compiler
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79
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80 procedure Timed_Protected_Entry_Call
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81 (Object : Entries.Protection_Entries_Access;
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82 E : Protected_Entry_Index;
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83 Uninterpreted_Data : System.Address;
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84 Timeout : Duration;
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85 Mode : Delay_Modes;
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86 Entry_Call_Successful : out Boolean);
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87 -- Same as the Protected_Entry_Call but with time-out specified.
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88 -- This routines is used when we do not use ATC mechanism to implement
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89 -- timed entry calls.
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90
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91 procedure Service_Entries (Object : Entries.Protection_Entries_Access);
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92 pragma Inline (Service_Entries);
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93
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94 procedure PO_Service_Entries
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95 (Self_ID : Task_Id;
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96 Object : Entries.Protection_Entries_Access;
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97 Unlock_Object : Boolean := True);
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98 -- Service all entry queues of the specified object, executing the
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99 -- corresponding bodies of any queued entry calls that are waiting
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100 -- on True barriers. This is used when the state of a protected
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101 -- object may have changed, in particular after the execution of
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102 -- the statement sequence of a protected procedure.
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103 --
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104 -- Note that servicing an entry may change the value of one or more
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105 -- barriers, so this routine keeps checking barriers until all of
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106 -- them are closed.
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107 --
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108 -- This must be called with abort deferred and with the corresponding
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109 -- object locked.
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110 --
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111 -- If Unlock_Object is set True, then Object is unlocked on return,
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112 -- otherwise Object remains locked and the caller is responsible for
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113 -- the required unlock.
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114
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115 procedure Complete_Entry_Body (Object : Entries.Protection_Entries_Access);
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116 -- Called from within an entry body procedure, indicates that the
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117 -- corresponding entry call has been serviced.
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118
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119 procedure Exceptional_Complete_Entry_Body
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120 (Object : Entries.Protection_Entries_Access;
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121 Ex : Ada.Exceptions.Exception_Id);
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122 -- Perform all of the functions of Complete_Entry_Body. In addition,
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123 -- report in Ex the exception whose propagation terminated the entry
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124 -- body to the runtime system.
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125
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126 procedure Cancel_Protected_Entry_Call (Block : in out Communication_Block);
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127 -- Attempt to cancel the most recent protected entry call. If the call is
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128 -- not queued abortably, wait until it is or until it has completed.
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129 -- If the call is actually cancelled, the called object will be
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130 -- locked on return from this call. Get_Cancelled (Block) can be
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131 -- used to determine if the cancellation took place; there
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132 -- may be entries needing service in this case.
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133 --
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134 -- Block passes information between this and other runtime calls.
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135
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136 function Enqueued (Block : Communication_Block) return Boolean;
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137 -- Returns True if the Protected_Entry_Call which returned the
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138 -- specified Block object was queued; False otherwise.
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139
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140 function Cancelled (Block : Communication_Block) return Boolean;
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141 -- Returns True if the Protected_Entry_Call which returned the
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142 -- specified Block object was cancelled, False otherwise.
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143
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144 procedure Requeue_Protected_Entry
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145 (Object : Entries.Protection_Entries_Access;
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146 New_Object : Entries.Protection_Entries_Access;
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147 E : Protected_Entry_Index;
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148 With_Abort : Boolean);
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149 -- If Object = New_Object, queue the protected entry call on Object
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150 -- currently being serviced on the queue corresponding to the entry
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151 -- represented by E.
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152 --
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153 -- If Object /= New_Object, transfer the call to New_Object.E,
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154 -- executing or queuing it as appropriate.
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155 --
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156 -- With_Abort---True if the call is to be queued abortably, false
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157 -- otherwise.
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158
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159 procedure Requeue_Task_To_Protected_Entry
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160 (New_Object : Entries.Protection_Entries_Access;
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161 E : Protected_Entry_Index;
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162 With_Abort : Boolean);
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163 -- Transfer task entry call currently being serviced to entry E
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164 -- on New_Object.
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165 --
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166 -- With_Abort---True if the call is to be queued abortably, false
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167 -- otherwise.
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168
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169 function Protected_Count
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170 (Object : Entries.Protection_Entries'Class;
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171 E : Protected_Entry_Index)
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172 return Natural;
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173 -- Return the number of entry calls to E on Object
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174
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175 function Protected_Entry_Caller
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176 (Object : Entries.Protection_Entries'Class) return Task_Id;
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177 -- Return value of E'Caller, where E is the protected entry currently
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178 -- being handled. This will only work if called from within an entry
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179 -- body, as required by the LRM (C.7.1(14)).
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180
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181 -- For internal use only
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182
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183 procedure PO_Do_Or_Queue
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184 (Self_ID : Task_Id;
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185 Object : Entries.Protection_Entries_Access;
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186 Entry_Call : Entry_Call_Link);
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187 -- This procedure either executes or queues an entry call, depending
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188 -- on the status of the corresponding barrier. It assumes that abort
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189 -- is deferred and that the specified object is locked.
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190
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191 private
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192 type Communication_Block is record
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193 Self : Task_Id;
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194 Enqueued : Boolean := True;
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195 Cancelled : Boolean := False;
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196 end record;
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197 pragma Volatile (Communication_Block);
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198
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199 -- When a program contains limited interfaces, the compiler generates the
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200 -- predefined primitives associated with dispatching selects. One of the
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201 -- parameters of these routines is of type Communication_Block. Even if
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202 -- the program lacks implementing concurrent types, the tasking runtime is
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203 -- dragged in unconditionally because of Communication_Block. To avoid this
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204 -- case, the compiler uses type Dummy_Communication_Block which defined in
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205 -- System.Soft_Links. If the structure of Communication_Block is changed,
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206 -- the corresponding dummy type must be changed as well.
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207
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208 -- The Communication_Block seems to be a relic. At the moment, the
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209 -- compiler seems to be generating unnecessary conditional code based on
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210 -- this block. See the code generated for async. select with task entry
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211 -- call for another way of solving this ???
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212
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213 end System.Tasking.Protected_Objects.Operations;
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