Mercurial > cpython-lru_cache-weakref

annotate Doc/lib/libresource.tex @ 25838:8540887bcec6 2.2

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Backport of 2.183: Fix memory leak in add_subclass() found by NealN with valgrind.
author Guido van Rossum <guido@python.org>
date Fri, 18 Oct 2002 13:42:21 +0000
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1 \section{\module{resource} ---
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2 Resource usage information}
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3
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4 \declaremodule{builtin}{resource}
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5 \platform{Unix}
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6 \modulesynopsis{An interface to provide resource usage information on
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7 the current process.}
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8 \moduleauthor{Jeremy Hylton}{jeremy@alum.mit.edu}
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9 \sectionauthor{Jeremy Hylton}{jeremy@alum.mit.edu}
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10
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11
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12 This module provides basic mechanisms for measuring and controlling
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13 system resources utilized by a program.
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14
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15 Symbolic constants are used to specify particular system resources and
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16 to request usage information about either the current process or its
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17 children.
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18
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19 A single exception is defined for errors:
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20
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21
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22 \begin{excdesc}{error}
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23 The functions described below may raise this error if the underlying
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24 system call failures unexpectedly.
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25 \end{excdesc}
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26
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27 \subsection{Resource Limits}
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28
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29 Resources usage can be limited using the \function{setrlimit()} function
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30 described below. Each resource is controlled by a pair of limits: a
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31 soft limit and a hard limit. The soft limit is the current limit, and
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32 may be lowered or raised by a process over time. The soft limit can
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33 never exceed the hard limit. The hard limit can be lowered to any
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34 value greater than the soft limit, but not raised. (Only processes with
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35 the effective UID of the super-user can raise a hard limit.)
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36
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37 The specific resources that can be limited are system dependent. They
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38 are described in the \manpage{getrlimit}{2} man page. The resources
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39 listed below are supported when the underlying operating system
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40 supports them; resources which cannot be checked or controlled by the
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41 operating system are not defined in this module for those platforms.
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42
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43 \begin{funcdesc}{getrlimit}{resource}
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44 Returns a tuple \code{(\var{soft}, \var{hard})} with the current
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45 soft and hard limits of \var{resource}. Raises \exception{ValueError} if
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46 an invalid resource is specified, or \exception{error} if the
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47 underyling system call fails unexpectedly.
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48 \end{funcdesc}
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49
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50 \begin{funcdesc}{setrlimit}{resource, limits}
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51 Sets new limits of consumption of \var{resource}. The \var{limits}
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52 argument must be a tuple \code{(\var{soft}, \var{hard})} of two
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53 integers describing the new limits. A value of \code{-1} can be used to
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54 specify the maximum possible upper limit.
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55
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56 Raises \exception{ValueError} if an invalid resource is specified,
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57 if the new soft limit exceeds the hard limit, or if a process tries
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58 to raise its hard limit (unless the process has an effective UID of
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59 super-user). Can also raise \exception{error} if the underyling
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60 system call fails.
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61 \end{funcdesc}
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62
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63 These symbols define resources whose consumption can be controlled
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64 using the \function{setrlimit()} and \function{getrlimit()} functions
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65 described below. The values of these symbols are exactly the constants
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66 used by \C{} programs.
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67
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68 The \UNIX{} man page for \manpage{getrlimit}{2} lists the available
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69 resources. Note that not all systems use the same symbol or same
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70 value to denote the same resource. This module does not attempt to
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71 mask platform differences --- symbols not defined for a platform will
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72 not be available from this module on that platform.
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73
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74 \begin{datadesc}{RLIMIT_CORE}
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75 The maximum size (in bytes) of a core file that the current process
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76 can create. This may result in the creation of a partial core file
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77 if a larger core would be required to contain the entire process
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78 image.
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79 \end{datadesc}
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80
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81 \begin{datadesc}{RLIMIT_CPU}
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82 The maximum amount of processor time (in seconds) that a process can
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83 use. If this limit is exceeded, a \constant{SIGXCPU} signal is sent to
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84 the process. (See the \refmodule{signal} module documentation for
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85 information about how to catch this signal and do something useful,
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86 e.g. flush open files to disk.)
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87 \end{datadesc}
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88
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89 \begin{datadesc}{RLIMIT_FSIZE}
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90 The maximum size of a file which the process may create. This only
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91 affects the stack of the main thread in a multi-threaded process.
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92 \end{datadesc}
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93
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94 \begin{datadesc}{RLIMIT_DATA}
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95 The maximum size (in bytes) of the process's heap.
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96 \end{datadesc}
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97
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98 \begin{datadesc}{RLIMIT_STACK}
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99 The maximum size (in bytes) of the call stack for the current
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100 process.
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101 \end{datadesc}
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102
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103 \begin{datadesc}{RLIMIT_RSS}
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104 The maximum resident set size that should be made available to the
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105 process.
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106 \end{datadesc}
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107
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108 \begin{datadesc}{RLIMIT_NPROC}
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109 The maximum number of processes the current process may create.
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110 \end{datadesc}
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111
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112 \begin{datadesc}{RLIMIT_NOFILE}
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113 The maximum number of open file descriptors for the current
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114 process.
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115 \end{datadesc}
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116
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117 \begin{datadesc}{RLIMIT_OFILE}
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118 The BSD name for \constant{RLIMIT_NOFILE}.
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119 \end{datadesc}
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120
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121 \begin{datadesc}{RLIMIT_MEMLOC}
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122 The maximm address space which may be locked in memory.
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123 \end{datadesc}
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124
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125 \begin{datadesc}{RLIMIT_VMEM}
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126 The largest area of mapped memory which the process may occupy.
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127 \end{datadesc}
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128
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129 \begin{datadesc}{RLIMIT_AS}
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130 The maximum area (in bytes) of address space which may be taken by
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131 the process.
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132 \end{datadesc}
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133
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134 \subsection{Resource Usage}
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135
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136 These functiona are used to retrieve resource usage information:
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137
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138 \begin{funcdesc}{getrusage}{who}
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139 This function returns a large tuple that describes the resources
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140 consumed by either the current process or its children, as specified
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141 by the \var{who} parameter. The \var{who} parameter should be
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142 specified using one of the \constant{RUSAGE_*} constants described
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143 below.
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144
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145 The elements of the return value each
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146 describe how a particular system resource has been used, e.g. amount
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147 of time spent running is user mode or number of times the process was
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148 swapped out of main memory. Some values are dependent on the clock
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149 tick internal, e.g. the amount of memory the process is using.
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150
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151 The first two elements of the return value are floating point values
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152 representing the amount of time spent executing in user mode and the
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153 amount of time spent executing in system mode, respectively. The
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154 remaining values are integers. Consult the \manpage{getrusage}{2}
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155 man page for detailed information about these values. A brief
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156 summary is presented here:
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157
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158 \begin{tableii}{r|l}{code}{Offset}{Resource}
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159 \lineii{0}{time in user mode (float)}
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160 \lineii{1}{time in system mode (float)}
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161 \lineii{2}{maximum resident set size}
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162 \lineii{3}{shared memory size}
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163 \lineii{4}{unshared memory size}
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164 \lineii{5}{unshared stack size}
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165 \lineii{6}{page faults not requiring I/O}
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166 \lineii{7}{page faults requiring I/O}
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167 \lineii{8}{number of swap outs}
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168 \lineii{9}{block input operations}
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169 \lineii{10}{block output operations}
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170 \lineii{11}{messages sent}
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171 \lineii{12}{messages received}
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172 \lineii{13}{signals received}
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173 \lineii{14}{voluntary context switches}
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174 \lineii{15}{involuntary context switches}
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175 \end{tableii}
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176
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177 This function will raise a \exception{ValueError} if an invalid
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178 \var{who} parameter is specified. It may also raise
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179 \exception{error} exception in unusual circumstances.
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180 \end{funcdesc}
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181
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182 \begin{funcdesc}{getpagesize}{}
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183 Returns the number of bytes in a system page. (This need not be the
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184 same as the hardware page size.) This function is useful for
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185 determining the number of bytes of memory a process is using. The
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186 third element of the tuple returned by \function{getrusage()} describes
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187 memory usage in pages; multiplying by page size produces number of
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188 bytes.
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189 \end{funcdesc}
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190
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191 The following \constant{RUSAGE_*} symbols are passed to the
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192 \function{getrusage()} function to specify which processes information
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193 should be provided for.
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194
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195 \begin{datadesc}{RUSAGE_SELF}
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196 \constant{RUSAGE_SELF} should be used to
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197 request information pertaining only to the process itself.
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198 \end{datadesc}
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199
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200 \begin{datadesc}{RUSAGE_CHILDREN}
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201 Pass to \function{getrusage()} to request resource information for
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202 child processes of the calling process.
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203 \end{datadesc}
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204
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205 \begin{datadesc}{RUSAGE_BOTH}
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206 Pass to \function{getrusage()} to request resources consumed by both
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207 the current process and child processes. May not be available on all
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208 systems.
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209 \end{datadesc}