mirror of https://github.com/mkerrisk/man-pages
262 lines
7.4 KiB
Groff
262 lines
7.4 KiB
Groff
.\" Copyright (c) 2012 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.TH MALLOC_INFO 3 2013-04-19 "GNU" "Linux Programmer's Manual"
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.SH NAME
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malloc_info \- export malloc state to a stream
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.SH SYNOPSIS
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.nf
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.B #include <malloc.h>
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.sp
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.BI "int malloc_info(int " options ", FILE *" stream );
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.fi
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.SH DESCRIPTION
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The
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.BR malloc_info ()
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function exports an XML string that describes the current state
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of the memory-allocation
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implementation in the caller.
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The string is printed on the file stream
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.IR stream .
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The exported string includes information about all arenas (see
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.BR malloc (3)).
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As currently implemented,
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.I options
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must be zero.
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.SH RETURN VALUE
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On success,
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.BR malloc_info ()
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returns 0;
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on error, it returns \-1, with
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.I errno
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set to indicate the cause.
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.SH ERRORS
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.TP
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.B EINVAL
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.I options
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was nonzero.
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.SH VERSIONS
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.BR malloc_info ()
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was added to glibc in version 2.10.
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.SH CONFORMING TO
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This function is a GNU extension.
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.SH NOTES
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The memory-allocation information is provided as an XML string
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(rather than a C structure)
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because the information may change over time
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(according to changes in the underlying implementation).
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The output XML string includes a version field.
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The
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.BR open_memstream (3)
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function can be used to send the output of
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.BR malloc_info ()
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directly into a buffer in memory, rather than to a file.
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The
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.BR malloc_info ()
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function is designed to address deficiencies in
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.BR malloc_stats (3)
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and
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.BR mallinfo (3).
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.SH EXAMPLE
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The program below takes up to four command-line arguments,
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of which the first three are mandatory.
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The first argument specifies the number of threads that
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the program should create.
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All of the threads, including the main thread,
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allocate the number of blocks of memory specified by the second argument.
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The third argument controls the size of the blocks to be allocated.
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The main thread creates blocks of this size,
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the second thread created by the program allocates blocks of twice this size,
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the third thread allocates blocks of three times this size, and so on.
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The program calls
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.BR malloc_info ()
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twice to display the memory-allocation state.
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The first call takes place before any threads
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are created or memory allocated.
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The second call is performed after all threads have allocated memory.
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In the following example,
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the command-line arguments specify the creation of one additional thread,
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and both the main thread and the additional thread
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allocate 10000 blocks of memory.
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After the blocks of memory have been allocated,
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.BR malloc_info ()
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shows the state of two allocation arenas.
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.in +4
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.nf
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.RB "$ " "getconf GNU_LIBC_VERSION"
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glibc 2.13
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.RB "$ " "./a.out 1 10000 100"
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============ Before allocating blocks ============
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<malloc version="1">
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<heap nr="0">
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<sizes>
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</sizes>
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<total type="fast" count="0" size="0"/>
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<total type="rest" count="0" size="0"/>
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<system type="current" size="135168"/>
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<system type="max" size="135168"/>
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<aspace type="total" size="135168"/>
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<aspace type="mprotect" size="135168"/>
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</heap>
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<total type="fast" count="0" size="0"/>
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<total type="rest" count="0" size="0"/>
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<system type="current" size="135168"/>
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<system type="max" size="135168"/>
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<aspace type="total" size="135168"/>
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<aspace type="mprotect" size="135168"/>
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</malloc>
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============ After allocating blocks ============
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<malloc version="1">
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<heap nr="0">
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<sizes>
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</sizes>
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<total type="fast" count="0" size="0"/>
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<total type="rest" count="0" size="0"/>
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<system type="current" size="1081344"/>
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<system type="max" size="1081344"/>
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<aspace type="total" size="1081344"/>
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<aspace type="mprotect" size="1081344"/>
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</heap>
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<heap nr="1">
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<sizes>
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</sizes>
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<total type="fast" count="0" size="0"/>
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<total type="rest" count="0" size="0"/>
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<system type="current" size="1032192"/>
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<system type="max" size="1032192"/>
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<aspace type="total" size="1032192"/>
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<aspace type="mprotect" size="1032192"/>
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</heap>
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<total type="fast" count="0" size="0"/>
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<total type="rest" count="0" size="0"/>
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<system type="current" size="2113536"/>
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<system type="max" size="2113536"/>
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<aspace type="total" size="2113536"/>
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<aspace type="mprotect" size="2113536"/>
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</malloc>
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.fi
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.in
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.SS Program source
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.nf
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#include <unistd.h>
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#include <stdlib.h>
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#include <pthread.h>
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#include <malloc.h>
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#include <errno.h>
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static size_t blockSize;
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static int numThreads, numBlocks;
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#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \\
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} while (0)
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static void *
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thread_func(void *arg)
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{
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int j;
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int tn = (int) arg;
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/* The multiplier \(aq(2 + tn)\(aq ensures that each thread (including
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the main thread) allocates a different amount of memory */
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for (j = 0; j < numBlocks; j++)
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if (malloc(blockSize * (2 + tn)) == NULL)
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errExit("malloc\-thread");
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sleep(100); /* Sleep until main thread terminates */
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return NULL;
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}
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int
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main(int argc, char *argv[])
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{
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int j, tn, sleepTime;
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pthread_t *thr;
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if (argc < 4) {
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fprintf(stderr,
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"%s num\-threads num\-blocks block\-size [sleep\-time]\\n",
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argv[0]);
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exit(EXIT_FAILURE);
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}
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numThreads = atoi(argv[1]);
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numBlocks = atoi(argv[2]);
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blockSize = atoi(argv[3]);
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sleepTime = (argc > 4) ? atoi(argv[4]) : 0;
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thr = calloc(numThreads, sizeof(pthread_t));
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if (thr == NULL)
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errExit("calloc");
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printf("============ Before allocating blocks ============\\n");
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malloc_info(0, stdout);
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/* Create threads that allocate different amounts of memory */
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for (tn = 0; tn < numThreads; tn++) {
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errno = pthread_create(&thr[tn], NULL, thread_func,
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(void *) tn);
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if (errno != 0)
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errExit("pthread_create");
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/* If we add a sleep interval after the start\-up of each
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thread, the threads likely won\(aqt contend for malloc
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mutexes, and therefore additional arenas won\(aqt be
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allocated (see malloc(3)). */
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if (sleepTime > 0)
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sleep(sleepTime);
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}
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/* The main thread also allocates some memory */
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for (j = 0; j < numBlocks; j++)
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if (malloc(blockSize) == NULL)
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errExit("malloc");
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sleep(2); /* Give all threads a chance to
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complete allocations */
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printf("\\n============ After allocating blocks ============\\n");
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malloc_info(0, stdout);
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exit(EXIT_SUCCESS);
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}
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.fi
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.SH SEE ALSO
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.BR mallinfo (3),
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.BR malloc (3),
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.BR malloc_stats (3),
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.BR mallopt (3),
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.BR open_memstream (3)
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