diff options
Diffstat (limited to 'demo')
| -rw-r--r-- | demo/ReadMe.txt | 54 | ||||
| -rw-r--r-- | demo/SampleIpcConversation.png | bin | 0 -> 11909 bytes | |||
| -rwxr-xr-x | demo/cleanup.py | 22 | ||||
| -rw-r--r-- | demo/conclusion.c | 146 | ||||
| -rw-r--r-- | demo/conclusion.py | 86 | ||||
| -rwxr-xr-x | demo/make_all.sh | 12 | ||||
| -rw-r--r-- | demo/md5.c | 381 | ||||
| -rw-r--r-- | demo/md5.h | 91 | ||||
| -rw-r--r-- | demo/params.txt | 20 | ||||
| -rw-r--r-- | demo/premise.c | 223 | ||||
| -rw-r--r-- | demo/premise.py | 118 | ||||
| -rw-r--r-- | demo/utils.c | 119 | ||||
| -rw-r--r-- | demo/utils.h | 18 | ||||
| -rw-r--r-- | demo/utils.py | 90 |
14 files changed, 1380 insertions, 0 deletions
diff --git a/demo/ReadMe.txt b/demo/ReadMe.txt new file mode 100644 index 0000000..56a35dd --- /dev/null +++ b/demo/ReadMe.txt @@ -0,0 +1,54 @@ +This demonstrates use of shared memory and semaphores via two applications +named after Mrs. Premise and Mrs. Conclusion of the Monty Python sketch. +http://www.youtube.com/watch?v=crIJvcWkVcs + +Like those two characters, these programs chat back and forth and the result +is a lot of nonsense. In this case, what the programs are saying isn't the +interesting part. What's interesting is how they're doing it. + +Mrs. Premise and Mrs. Conclusion (the programs, not the sketch characters) +communicate through POSIX shared memory with a semaphore to control access +to that memory. + +Mrs. Premise starts things off by creating the shared memory and semaphore +and writing a random string (the current time) to the memory. She then sits +in a loop reading the memory. If it holds the same message she wrote, she +does nothing. If it is a new message, it must be from Mrs. Conclusion. + +Meanwhile, Mrs. Conclusion is doing exactly the same thing, except that she +assumes Mrs. Premise will write the first message. + +When either of these programs reads a new message, they write back an md5 +hash of that message. This serves two purposes. First, it ensures that +subsequent messages are very different so that if a message somehow gets +corrupted (say by being partially overwritten by the next message), it will +not escape notice. Second, it ensures that corruption can be detected if +it happens, because Mrs. Premise and Mrs. Conclusion can calculate what the +other's response to their message should be. + +Since they use a semaphore to control access to the shared memory, Mrs. +Premise and Mrs. Conclusion won't ever find their messages corrupted no +matter how many messages they exchange. You can experiment with this by +setting ITERATIONS in params.txt to a very large value. You can change +LIVE_DANGEROUSLY (also in params.txt) to a non-zero value to tell Mrs. +Premise and Mrs. Conclusion to run without using the semaphore. The shared +memory will probably get corrupted in fewer than 1000 iterations. + +To run the demo, start Mrs. Premise first in one window and then run +Mrs. Conclusion in another. + + + The Fancy Version + ================= + +If you want to get fancy, you can play with C versions of Mrs. Premise and +Mrs. Conclusion. The script make_all.sh will compile them for you. (Linux +users will need to edit the script and uncomment the line for the +Linux-specific linker option.) + +The resulting executables are called premise and conclusion and work exactly +the same as their Python counterparts. You can have the two C programs talk +to one another, or you can have premise.py talk to the C version of +conclusion...the possibilities are endless. (Actually, there are only four +possible combinations but "endless" sounds better.) + diff --git a/demo/SampleIpcConversation.png b/demo/SampleIpcConversation.png Binary files differnew file mode 100644 index 0000000..9d11e7a --- /dev/null +++ b/demo/SampleIpcConversation.png diff --git a/demo/cleanup.py b/demo/cleanup.py new file mode 100755 index 0000000..afe4178 --- /dev/null +++ b/demo/cleanup.py @@ -0,0 +1,22 @@ +import posix_ipc +import utils + +params = utils.read_params() + +try: + posix_ipc.unlink_shared_memory(params["SHARED_MEMORY_NAME"]) + s = "memory segment %s removed" % params["SHARED_MEMORY_NAME"] + print (s) +except: + print ("memory doesn't need cleanup") + + +try: + posix_ipc.unlink_semaphore(params["SEMAPHORE_NAME"]) + s = "semaphore %s removed" % params["SEMAPHORE_NAME"] + print (s) +except: + print ("semaphore doesn't need cleanup") + + +print ("\nAll clean!") diff --git a/demo/conclusion.c b/demo/conclusion.c new file mode 100644 index 0000000..3807efd --- /dev/null +++ b/demo/conclusion.c @@ -0,0 +1,146 @@ +#include <stdio.h> +#include <errno.h> +#include <unistd.h> +#include <string.h> +#include <time.h> +#include <semaphore.h> +#include <sys/types.h> +#include <sys/mman.h> +#include <fcntl.h> + +#include "md5.h" +#include "utils.h" + +static const char MY_NAME[] = "Mrs. Conclusion"; + +// Set up a Mrs. Premise & Mrs. Conclusion conversation. + +int main() { + sem_t *the_semaphore = NULL; + int rc; + char s[1024]; + int i; + int done; + int fd; + void *pSharedMemory = NULL; + char last_message_i_wrote[256]; + char md5ified_message[256]; + struct param_struct params; + + say(MY_NAME, "Oooo 'ello, I'm Mrs. Conclusion!"); + + read_params(¶ms); + + // Mrs. Premise has already created the semaphore and shared memory. + // I just need to get handles to them. + the_semaphore = sem_open(params.semaphore_name, 0); + + if (the_semaphore == SEM_FAILED) { + the_semaphore = NULL; + sprintf(s, "Getting a handle to the semaphore failed; errno is %d", errno); + say(MY_NAME, s); + } + else { + // get a handle to the shared memory + fd = shm_open(params.shared_memory_name, O_RDWR, params.permissions); + + if (fd == -1) { + sprintf(s, "Couldn't get a handle to the shared memory; errno is %d", errno); + say(MY_NAME, s); + } + else { + // mmap it. + pSharedMemory = mmap((void *)0, (size_t)params.size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + if (pSharedMemory == MAP_FAILED) { + sprintf(s, "MMapping the shared memory failed; errno is %d", errno); + say(MY_NAME, s); + } + else { + sprintf(s, "pSharedMemory = %p", pSharedMemory); + say(MY_NAME, s); + + i = 0; + done = 0; + last_message_i_wrote[0] = '\0'; + while (!done) { + sprintf(s, "iteration %d", i); + say(MY_NAME, s); + + // Wait for Mrs. Premise to free up the semaphore. + rc = acquire_semaphore(MY_NAME, the_semaphore, params.live_dangerously); + if (rc) + done = 1; + else { + while ( (!rc) && \ + (!strcmp((char *)pSharedMemory, last_message_i_wrote)) + ) { + // Nothing new; give Mrs. Premise another change to respond. + sprintf(s, "Read %zu characters '%s'", strlen((char *)pSharedMemory), (char *)pSharedMemory); + say(MY_NAME, s); + say(MY_NAME, "Releasing the semaphore"); + rc = release_semaphore(MY_NAME, the_semaphore, params.live_dangerously); + if (!rc) { + say(MY_NAME, "Waiting to acquire the semaphore"); + rc = acquire_semaphore(MY_NAME, the_semaphore, params.live_dangerously); + } + } + + md5ify(last_message_i_wrote, md5ified_message); + + // I always accept the first message (when i == 0) + if ( (i == 0) || (!strcmp(md5ified_message, (char *)pSharedMemory)) ) { + // All is well + i++; + + if (i == params.iterations) + done = 1; + + // MD5 the reply and write back to Mrs. Premise. + md5ify((char *)pSharedMemory, md5ified_message); + + // Write back to Mrs. Premise. + sprintf(s, "Writing %zu characters '%s'", strlen(md5ified_message), md5ified_message); + say(MY_NAME, s); + + strcpy((char *)pSharedMemory, md5ified_message); + + strcpy(last_message_i_wrote, md5ified_message); + } + else { + sprintf(s, "Shared memory corruption after %d iterations.", i); + say(MY_NAME, s); + sprintf(s, "Mismatch; rc = %d, new message is '%s', expected '%s'.", rc, (char *)pSharedMemory, md5ified_message); + say(MY_NAME, s); + done = 1; + } + } + + // Release the semaphore. + rc = release_semaphore(MY_NAME, the_semaphore, params.live_dangerously); + if (rc) + done = 1; + } + } + // Un-mmap the memory + rc = munmap(pSharedMemory, (size_t)params.size); + if (rc) { + sprintf(s, "Unmapping the memory failed; errno is %d", errno); + say(MY_NAME, s); + } + + // Close the shared memory segment's file descriptor + if (-1 == close(fd)) { + sprintf(s, "Closing memory's file descriptor failed; errno is %d", errno); + say(MY_NAME, s); + } + } + rc = sem_close(the_semaphore); + if (rc) { + sprintf(s, "Closing the semaphore failed; errno is %d", errno); + say(MY_NAME, s); + } + } + + + return 0; +} diff --git a/demo/conclusion.py b/demo/conclusion.py new file mode 100644 index 0000000..7ecd05b --- /dev/null +++ b/demo/conclusion.py @@ -0,0 +1,86 @@ +# Python modules +import time +import mmap +import os +import sys +PY_MAJOR_VERSION = sys.version_info[0] +# hashlib is only available in Python >= 2.5. I still want to support +# older Pythons so I import md5 if hashlib is not available. Fortunately +# md5 can masquerade as hashlib for my purposes. +try: + import hashlib +except ImportError: + import md5 as hashlib + +# 3rd party modules +import posix_ipc + +# Utils for this demo +import utils + + +PY_MAJOR_VERSION = sys.version_info[0] + +utils.say("Oooo 'ello, I'm Mrs. Conclusion!") + +params = utils.read_params() + +# Mrs. Premise has already created the semaphore and shared memory. +# I just need to get handles to them. +memory = posix_ipc.SharedMemory(params["SHARED_MEMORY_NAME"]) +semaphore = posix_ipc.Semaphore(params["SEMAPHORE_NAME"]) + +# MMap the shared memory +mapfile = mmap.mmap(memory.fd, memory.size) + +# Once I've mmapped the file descriptor, I can close it without +# interfering with the mmap. This also demonstrates that os.close() is a +# perfectly legitimate alternative to the SharedMemory's close_fd() method. +os.close(memory.fd) + +what_i_wrote = "" + +for i in range(0, params["ITERATIONS"]): + utils.say("iteration %d" % i) + if not params["LIVE_DANGEROUSLY"]: + # Wait for Mrs. Premise to free up the semaphore. + utils.say("Waiting to acquire the semaphore") + semaphore.acquire() + + s = utils.read_from_memory(mapfile) + + while s == what_i_wrote: + if not params["LIVE_DANGEROUSLY"]: + # Release the semaphore... + utils.say("Releasing the semaphore") + semaphore.release() + # ...and wait for it to become available again. + utils.say("Waiting to acquire the semaphore") + semaphore.acquire() + + s = utils.read_from_memory(mapfile) + + if what_i_wrote: + if PY_MAJOR_VERSION > 2: + what_i_wrote = what_i_wrote.encode() + try: + assert(s == hashlib.md5(what_i_wrote).hexdigest()) + except AssertionError: + utils.raise_error(AssertionError, + "Shared memory corruption after %d iterations." % i) + + if PY_MAJOR_VERSION > 2: + s = s.encode() + what_i_wrote = hashlib.md5(s).hexdigest() + + utils.write_to_memory(mapfile, what_i_wrote) + + if not params["LIVE_DANGEROUSLY"]: + utils.say("Releasing the semaphore") + semaphore.release() + +semaphore.close() +mapfile.close() + +utils.say("") +utils.say("%d iterations complete" % (i + 1)) diff --git a/demo/make_all.sh b/demo/make_all.sh new file mode 100755 index 0000000..baa8722 --- /dev/null +++ b/demo/make_all.sh @@ -0,0 +1,12 @@ +#!/usr/bin/env bash + +# Linker opts is blank for OS X, FreeBSD and OpenSolaris +#LINKER_OPTIONS="" + +# Must link with realtime libs for Linux +LINKER_OPTIONS="-lrt" + +gcc -Wall -c -o md5.o md5.c +gcc -Wall -c -o utils.o utils.c +gcc -Wall -L. $LINKER_OPTIONS md5.o utils.o -o premise premise.c +gcc -Wall -L. $LINKER_OPTIONS md5.o utils.o -o conclusion conclusion.c diff --git a/demo/md5.c b/demo/md5.c new file mode 100644 index 0000000..c35d96c --- /dev/null +++ b/demo/md5.c @@ -0,0 +1,381 @@ +/* + Copyright (C) 1999, 2000, 2002 Aladdin Enterprises. All rights reserved. + + This software is provided 'as-is', without any express or implied + warranty. In no event will the authors be held liable for any damages + arising from the use of this software. + + Permission is granted to anyone to use this software for any purpose, + including commercial applications, and to alter it and redistribute it + freely, subject to the following restrictions: + + 1. The origin of this software must not be misrepresented; you must not + claim that you wrote the original software. If you use this software + in a product, an acknowledgment in the product documentation would be + appreciated but is not required. + 2. Altered source versions must be plainly marked as such, and must not be + misrepresented as being the original software. + 3. This notice may not be removed or altered from any source distribution. + + L. Peter Deutsch + ghost@aladdin.com + + */ +/* $Id: md5.c,v 1.6 2002/04/13 19:20:28 lpd Exp $ */ +/* + Independent implementation of MD5 (RFC 1321). + + This code implements the MD5 Algorithm defined in RFC 1321, whose + text is available at + http://www.ietf.org/rfc/rfc1321.txt + The code is derived from the text of the RFC, including the test suite + (section A.5) but excluding the rest of Appendix A. It does not include + any code or documentation that is identified in the RFC as being + copyrighted. + + The original and principal author of md5.c is L. Peter Deutsch + <ghost@aladdin.com>. Other authors are noted in the change history + that follows (in reverse chronological order): + + 2002-04-13 lpd Clarified derivation from RFC 1321; now handles byte order + either statically or dynamically; added missing #include <string.h> + in library. + 2002-03-11 lpd Corrected argument list for main(), and added int return + type, in test program and T value program. + 2002-02-21 lpd Added missing #include <stdio.h> in test program. + 2000-07-03 lpd Patched to eliminate warnings about "constant is + unsigned in ANSI C, signed in traditional"; made test program + self-checking. + 1999-11-04 lpd Edited comments slightly for automatic TOC extraction. + 1999-10-18 lpd Fixed typo in header comment (ansi2knr rather than md5). + 1999-05-03 lpd Original version. + */ + +#include "md5.h" +#include <string.h> + +#undef BYTE_ORDER /* 1 = big-endian, -1 = little-endian, 0 = unknown */ +#ifdef ARCH_IS_BIG_ENDIAN +# define BYTE_ORDER (ARCH_IS_BIG_ENDIAN ? 1 : -1) +#else +# define BYTE_ORDER 0 +#endif + +#define T_MASK ((md5_word_t)~0) +#define T1 /* 0xd76aa478 */ (T_MASK ^ 0x28955b87) +#define T2 /* 0xe8c7b756 */ (T_MASK ^ 0x173848a9) +#define T3 0x242070db +#define T4 /* 0xc1bdceee */ (T_MASK ^ 0x3e423111) +#define T5 /* 0xf57c0faf */ (T_MASK ^ 0x0a83f050) +#define T6 0x4787c62a +#define T7 /* 0xa8304613 */ (T_MASK ^ 0x57cfb9ec) +#define T8 /* 0xfd469501 */ (T_MASK ^ 0x02b96afe) +#define T9 0x698098d8 +#define T10 /* 0x8b44f7af */ (T_MASK ^ 0x74bb0850) +#define T11 /* 0xffff5bb1 */ (T_MASK ^ 0x0000a44e) +#define T12 /* 0x895cd7be */ (T_MASK ^ 0x76a32841) +#define T13 0x6b901122 +#define T14 /* 0xfd987193 */ (T_MASK ^ 0x02678e6c) +#define T15 /* 0xa679438e */ (T_MASK ^ 0x5986bc71) +#define T16 0x49b40821 +#define T17 /* 0xf61e2562 */ (T_MASK ^ 0x09e1da9d) +#define T18 /* 0xc040b340 */ (T_MASK ^ 0x3fbf4cbf) +#define T19 0x265e5a51 +#define T20 /* 0xe9b6c7aa */ (T_MASK ^ 0x16493855) +#define T21 /* 0xd62f105d */ (T_MASK ^ 0x29d0efa2) +#define T22 0x02441453 +#define T23 /* 0xd8a1e681 */ (T_MASK ^ 0x275e197e) +#define T24 /* 0xe7d3fbc8 */ (T_MASK ^ 0x182c0437) +#define T25 0x21e1cde6 +#define T26 /* 0xc33707d6 */ (T_MASK ^ 0x3cc8f829) +#define T27 /* 0xf4d50d87 */ (T_MASK ^ 0x0b2af278) +#define T28 0x455a14ed +#define T29 /* 0xa9e3e905 */ (T_MASK ^ 0x561c16fa) +#define T30 /* 0xfcefa3f8 */ (T_MASK ^ 0x03105c07) +#define T31 0x676f02d9 +#define T32 /* 0x8d2a4c8a */ (T_MASK ^ 0x72d5b375) +#define T33 /* 0xfffa3942 */ (T_MASK ^ 0x0005c6bd) +#define T34 /* 0x8771f681 */ (T_MASK ^ 0x788e097e) +#define T35 0x6d9d6122 +#define T36 /* 0xfde5380c */ (T_MASK ^ 0x021ac7f3) +#define T37 /* 0xa4beea44 */ (T_MASK ^ 0x5b4115bb) +#define T38 0x4bdecfa9 +#define T39 /* 0xf6bb4b60 */ (T_MASK ^ 0x0944b49f) +#define T40 /* 0xbebfbc70 */ (T_MASK ^ 0x4140438f) +#define T41 0x289b7ec6 +#define T42 /* 0xeaa127fa */ (T_MASK ^ 0x155ed805) +#define T43 /* 0xd4ef3085 */ (T_MASK ^ 0x2b10cf7a) +#define T44 0x04881d05 +#define T45 /* 0xd9d4d039 */ (T_MASK ^ 0x262b2fc6) +#define T46 /* 0xe6db99e5 */ (T_MASK ^ 0x1924661a) +#define T47 0x1fa27cf8 +#define T48 /* 0xc4ac5665 */ (T_MASK ^ 0x3b53a99a) +#define T49 /* 0xf4292244 */ (T_MASK ^ 0x0bd6ddbb) +#define T50 0x432aff97 +#define T51 /* 0xab9423a7 */ (T_MASK ^ 0x546bdc58) +#define T52 /* 0xfc93a039 */ (T_MASK ^ 0x036c5fc6) +#define T53 0x655b59c3 +#define T54 /* 0x8f0ccc92 */ (T_MASK ^ 0x70f3336d) +#define T55 /* 0xffeff47d */ (T_MASK ^ 0x00100b82) +#define T56 /* 0x85845dd1 */ (T_MASK ^ 0x7a7ba22e) +#define T57 0x6fa87e4f +#define T58 /* 0xfe2ce6e0 */ (T_MASK ^ 0x01d3191f) +#define T59 /* 0xa3014314 */ (T_MASK ^ 0x5cfebceb) +#define T60 0x4e0811a1 +#define T61 /* 0xf7537e82 */ (T_MASK ^ 0x08ac817d) +#define T62 /* 0xbd3af235 */ (T_MASK ^ 0x42c50dca) +#define T63 0x2ad7d2bb +#define T64 /* 0xeb86d391 */ (T_MASK ^ 0x14792c6e) + + +static void +md5_process(md5_state_t *pms, const md5_byte_t *data /*[64]*/) +{ + md5_word_t + a = pms->abcd[0], b = pms->abcd[1], + c = pms->abcd[2], d = pms->abcd[3]; + md5_word_t t; +#if BYTE_ORDER > 0 + /* Define storage only for big-endian CPUs. */ + md5_word_t X[16]; +#else + /* Define storage for little-endian or both types of CPUs. */ + md5_word_t xbuf[16]; + const md5_word_t *X; +#endif + + { +#if BYTE_ORDER == 0 + /* + * Determine dynamically whether this is a big-endian or + * little-endian machine, since we can use a more efficient + * algorithm on the latter. + */ + static const int w = 1; + + if (*((const md5_byte_t *)&w)) /* dynamic little-endian */ +#endif +#if BYTE_ORDER <= 0 /* little-endian */ + { + /* + * On little-endian machines, we can process properly aligned + * data without copying it. + */ + if (!((data - (const md5_byte_t *)0) & 3)) { + /* data are properly aligned */ + X = (const md5_word_t *)data; + } else { + /* not aligned */ + memcpy(xbuf, data, 64); + X = xbuf; + } + } +#endif +#if BYTE_ORDER == 0 + else /* dynamic big-endian */ +#endif +#if BYTE_ORDER >= 0 /* big-endian */ + { + /* + * On big-endian machines, we must arrange the bytes in the + * right order. + */ + const md5_byte_t *xp = data; + int i; + +# if BYTE_ORDER == 0 + X = xbuf; /* (dynamic only) */ +# else +# define xbuf X /* (static only) */ +# endif + for (i = 0; i < 16; ++i, xp += 4) + xbuf[i] = xp[0] + (xp[1] << 8) + (xp[2] << 16) + (xp[3] << 24); + } +#endif + } + +#define ROTATE_LEFT(x, n) (((x) << (n)) | ((x) >> (32 - (n)))) + + /* Round 1. */ + /* Let [abcd k s i] denote the operation + a = b + ((a + F(b,c,d) + X[k] + T[i]) <<< s). */ +#define F(x, y, z) (((x) & (y)) | (~(x) & (z))) +#define SET(a, b, c, d, k, s, Ti)\ + t = a + F(b,c,d) + X[k] + Ti;\ + a = ROTATE_LEFT(t, s) + b + /* Do the following 16 operations. */ + SET(a, b, c, d, 0, 7, T1); + SET(d, a, b, c, 1, 12, T2); + SET(c, d, a, b, 2, 17, T3); + SET(b, c, d, a, 3, 22, T4); + SET(a, b, c, d, 4, 7, T5); + SET(d, a, b, c, 5, 12, T6); + SET(c, d, a, b, 6, 17, T7); + SET(b, c, d, a, 7, 22, T8); + SET(a, b, c, d, 8, 7, T9); + SET(d, a, b, c, 9, 12, T10); + SET(c, d, a, b, 10, 17, T11); + SET(b, c, d, a, 11, 22, T12); + SET(a, b, c, d, 12, 7, T13); + SET(d, a, b, c, 13, 12, T14); + SET(c, d, a, b, 14, 17, T15); + SET(b, c, d, a, 15, 22, T16); +#undef SET + + /* Round 2. */ + /* Let [abcd k s i] denote the operation + a = b + ((a + G(b,c,d) + X[k] + T[i]) <<< s). */ +#define G(x, y, z) (((x) & (z)) | ((y) & ~(z))) +#define SET(a, b, c, d, k, s, Ti)\ + t = a + G(b,c,d) + X[k] + Ti;\ + a = ROTATE_LEFT(t, s) + b + /* Do the following 16 operations. */ + SET(a, b, c, d, 1, 5, T17); + SET(d, a, b, c, 6, 9, T18); + SET(c, d, a, b, 11, 14, T19); + SET(b, c, d, a, 0, 20, T20); + SET(a, b, c, d, 5, 5, T21); + SET(d, a, b, c, 10, 9, T22); + SET(c, d, a, b, 15, 14, T23); + SET(b, c, d, a, 4, 20, T24); + SET(a, b, c, d, 9, 5, T25); + SET(d, a, b, c, 14, 9, T26); + SET(c, d, a, b, 3, 14, T27); + SET(b, c, d, a, 8, 20, T28); + SET(a, b, c, d, 13, 5, T29); + SET(d, a, b, c, 2, 9, T30); + SET(c, d, a, b, 7, 14, T31); + SET(b, c, d, a, 12, 20, T32); +#undef SET + + /* Round 3. */ + /* Let [abcd k s t] denote the operation + a = b + ((a + H(b,c,d) + X[k] + T[i]) <<< s). */ +#define H(x, y, z) ((x) ^ (y) ^ (z)) +#define SET(a, b, c, d, k, s, Ti)\ + t = a + H(b,c,d) + X[k] + Ti;\ + a = ROTATE_LEFT(t, s) + b + /* Do the following 16 operations. */ + SET(a, b, c, d, 5, 4, T33); + SET(d, a, b, c, 8, 11, T34); + SET(c, d, a, b, 11, 16, T35); + SET(b, c, d, a, 14, 23, T36); + SET(a, b, c, d, 1, 4, T37); + SET(d, a, b, c, 4, 11, T38); + SET(c, d, a, b, 7, 16, T39); + SET(b, c, d, a, 10, 23, T40); + SET(a, b, c, d, 13, 4, T41); + SET(d, a, b, c, 0, 11, T42); + SET(c, d, a, b, 3, 16, T43); + SET(b, c, d, a, 6, 23, T44); + SET(a, b, c, d, 9, 4, T45); + SET(d, a, b, c, 12, 11, T46); + SET(c, d, a, b, 15, 16, T47); + SET(b, c, d, a, 2, 23, T48); +#undef SET + + /* Round 4. */ + /* Let [abcd k s t] denote the operation + a = b + ((a + I(b,c,d) + X[k] + T[i]) <<< s). */ +#define I(x, y, z) ((y) ^ ((x) | ~(z))) +#define SET(a, b, c, d, k, s, Ti)\ + t = a + I(b,c,d) + X[k] + Ti;\ + a = ROTATE_LEFT(t, s) + b + /* Do the following 16 operations. */ + SET(a, b, c, d, 0, 6, T49); + SET(d, a, b, c, 7, 10, T50); + SET(c, d, a, b, 14, 15, T51); + SET(b, c, d, a, 5, 21, T52); + SET(a, b, c, d, 12, 6, T53); + SET(d, a, b, c, 3, 10, T54); + SET(c, d, a, b, 10, 15, T55); + SET(b, c, d, a, 1, 21, T56); + SET(a, b, c, d, 8, 6, T57); + SET(d, a, b, c, 15, 10, T58); + SET(c, d, a, b, 6, 15, T59); + SET(b, c, d, a, 13, 21, T60); + SET(a, b, c, d, 4, 6, T61); + SET(d, a, b, c, 11, 10, T62); + SET(c, d, a, b, 2, 15, T63); + SET(b, c, d, a, 9, 21, T64); +#undef SET + + /* Then perform the following additions. (That is increment each + of the four registers by the value it had before this block + was started.) */ + pms->abcd[0] += a; + pms->abcd[1] += b; + pms->abcd[2] += c; + pms->abcd[3] += d; +} + +void +md5_init(md5_state_t *pms) +{ + pms->count[0] = pms->count[1] = 0; + pms->abcd[0] = 0x67452301; + pms->abcd[1] = /*0xefcdab89*/ T_MASK ^ 0x10325476; + pms->abcd[2] = /*0x98badcfe*/ T_MASK ^ 0x67452301; + pms->abcd[3] = 0x10325476; +} + +void +md5_append(md5_state_t *pms, const md5_byte_t *data, int nbytes) +{ + const md5_byte_t *p = data; + int left = nbytes; + int offset = (pms->count[0] >> 3) & 63; + md5_word_t nbits = (md5_word_t)(nbytes << 3); + + if (nbytes <= 0) + return; + + /* Update the message length. */ + pms->count[1] += nbytes >> 29; + pms->count[0] += nbits; + if (pms->count[0] < nbits) + pms->count[1]++; + + /* Process an initial partial block. */ + if (offset) { + int copy = (offset + nbytes > 64 ? 64 - offset : nbytes); + + memcpy(pms->buf + offset, p, copy); + if (offset + copy < 64) + return; + p += copy; + left -= copy; + md5_process(pms, pms->buf); + } + + /* Process full blocks. */ + for (; left >= 64; p += 64, left -= 64) + md5_process(pms, p); + + /* Process a final partial block. */ + if (left) + memcpy(pms->buf, p, left); +} + +void +md5_finish(md5_state_t *pms, md5_byte_t digest[16]) +{ + static const md5_byte_t pad[64] = { + 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, + 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, + 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, + 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 + }; + md5_byte_t data[8]; + int i; + + /* Save the length before padding. */ + for (i = 0; i < 8; ++i) + data[i] = (md5_byte_t)(pms->count[i >> 2] >> ((i & 3) << 3)); + /* Pad to 56 bytes mod 64. */ + md5_append(pms, pad, ((55 - (pms->count[0] >> 3)) & 63) + 1); + /* Append the length. */ + md5_append(pms, data, 8); + for (i = 0; i < 16; ++i) + digest[i] = (md5_byte_t)(pms->abcd[i >> 2] >> ((i & 3) << 3)); +} diff --git a/demo/md5.h b/demo/md5.h new file mode 100644 index 0000000..698c995 --- /dev/null +++ b/demo/md5.h @@ -0,0 +1,91 @@ +/* + Copyright (C) 1999, 2002 Aladdin Enterprises. All rights reserved. + + This software is provided 'as-is', without any express or implied + warranty. In no event will the authors be held liable for any damages + arising from the use of this software. + + Permission is granted to anyone to use this software for any purpose, + including commercial applications, and to alter it and redistribute it + freely, subject to the following restrictions: + + 1. The origin of this software must not be misrepresented; you must not + claim that you wrote the original software. If you use this software + in a product, an acknowledgment in the product documentation would be + appreciated but is not required. + 2. Altered source versions must be plainly marked as such, and must not be + misrepresented as being the original software. + 3. This notice may not be removed or altered from any source distribution. + + L. Peter Deutsch + ghost@aladdin.com + + */ +/* $Id: md5.h,v 1.4 2002/04/13 19:20:28 lpd Exp $ */ +/* + Independent implementation of MD5 (RFC 1321). + + This code implements the MD5 Algorithm defined in RFC 1321, whose + text is available at + http://www.ietf.org/rfc/rfc1321.txt + The code is derived from the text of the RFC, including the test suite + (section A.5) but excluding the rest of Appendix A. It does not include + any code or documentation that is identified in the RFC as being + copyrighted. + + The original and principal author of md5.h is L. Peter Deutsch + <ghost@aladdin.com>. Other authors are noted in the change history + that follows (in reverse chronological order): + + 2002-04-13 lpd Removed support for non-ANSI compilers; removed + references to Ghostscript; clarified derivation from RFC 1321; + now handles byte order either statically or dynamically. + 1999-11-04 lpd Edited comments slightly for automatic TOC extraction. + 1999-10-18 lpd Fixed typo in header comment (ansi2knr rather than md5); + added conditionalization for C++ compilation from Martin + Purschke <purschke@bnl.gov>. + 1999-05-03 lpd Original version. + */ + +#ifndef md5_INCLUDED +# define md5_INCLUDED + +/* + * This package supports both compile-time and run-time determination of CPU + * byte order. If ARCH_IS_BIG_ENDIAN is defined as 0, the code will be + * compiled to run only on little-endian CPUs; if ARCH_IS_BIG_ENDIAN is + * defined as non-zero, the code will be compiled to run only on big-endian + * CPUs; if ARCH_IS_BIG_ENDIAN is not defined, the code will be compiled to + * run on either big- or little-endian CPUs, but will run slightly less + * efficiently on either one than if ARCH_IS_BIG_ENDIAN is defined. + */ + +typedef unsigned char md5_byte_t; /* 8-bit byte */ +typedef unsigned int md5_word_t; /* 32-bit word */ + +/* Define the state of the MD5 Algorithm. */ +typedef struct md5_state_s { + md5_word_t count[2]; /* message length in bits, lsw first */ + md5_word_t abcd[4]; /* digest buffer */ + md5_byte_t buf[64]; /* accumulate block */ +} md5_state_t; + +#ifdef __cplusplus +extern "C" +{ +#endif + +/* Initialize the algorithm. */ +void md5_init(md5_state_t *pms); + +/* Append a string to the message. */ +void md5_append(md5_state_t *pms, const md5_byte_t *data, int nbytes); + +/* Finish the message and return the digest. */ +void md5_finish(md5_state_t *pms, md5_byte_t digest[16]); + +#ifdef __cplusplus +} /* end extern "C" */ +#endif + +#endif /* md5_INCLUDED */ diff --git a/demo/params.txt b/demo/params.txt new file mode 100644 index 0000000..dc468c6 --- /dev/null +++ b/demo/params.txt @@ -0,0 +1,20 @@ +# These parameters control how Mrs. Premise and Mrs. Conclusion behave. + +# ITERATIONS is the number of times they'll talk to one another. +# LIVE_DANGEROUSLY is a Boolean (0 or 1); if set to 1 the programs +# won't use the semaphore to coordinate access to the shared +# memory. Corruption will likely result. +# SEMAPHORE_NAME is the name to be used for the semaphore. +# SHARED_MEMORY_NAME is the name to be used for the shared memory. +# PERMISSIONS are in octal (note the leading 0). +# SHM_SIZE is the size of the shared memory segment in bytes. + +ITERATIONS=1000 +LIVE_DANGEROUSLY=0 +SEMAPHORE_NAME=/wuthering_heights +SHARED_MEMORY_NAME=/four_yorkshiremen +PERMISSIONS=0600 +SHM_SIZE=4096 + + + diff --git a/demo/premise.c b/demo/premise.c new file mode 100644 index 0000000..43d5207 --- /dev/null +++ b/demo/premise.c @@ -0,0 +1,223 @@ +#include <stdio.h> +#include <errno.h> +#include <unistd.h> +#include <string.h> +#include <time.h> +#include <semaphore.h> +#include <sys/types.h> +#include <sys/mman.h> +#include <fcntl.h> +#include <stdarg.h> + +#include "md5.h" +#include "utils.h" + +const char MY_NAME[] = "Mrs. Premise"; + +// Set up a Mrs. Premise & Mrs. Conclusion conversation. + +void get_current_time(char *); + +int main() { + sem_t *pSemaphore = NULL; + int rc; + char s[1024]; + void *pSharedMemory = NULL; + char last_message_i_wrote[256]; + char md5ified_message[256]; + int i = 0; + int done = 0; + int fd; + struct param_struct params; + + say(MY_NAME, "Oooo 'ello, I'm Mrs. Premise!"); + + read_params(¶ms); + + // Create the shared memory + fd = shm_open(params.shared_memory_name, O_RDWR | O_CREAT | O_EXCL, params.permissions); + + if (fd == -1) { + fd = 0; + sprintf(s, "Creating the shared memory failed; errno is %d", errno); + say(MY_NAME, s); + } + else { + // The memory is created as a file that's 0 bytes long. Resize it. + rc = ftruncate(fd, params.size); + if (rc) { + sprintf(s, "Resizing the shared memory failed; errno is %d", errno); + say(MY_NAME, s); + } + else { + // MMap the shared memory + //void *mmap(void *start, size_t length, int prot, int flags, int fd, off_t offset); + pSharedMemory = mmap((void *)0, (size_t)params.size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + if (pSharedMemory == MAP_FAILED) { + pSharedMemory = NULL; + sprintf(s, "MMapping the shared memory failed; errno is %d", errno); + say(MY_NAME, s); + } + else { + sprintf(s, "pSharedMemory = %p", pSharedMemory); + say(MY_NAME, s); + } + } + } + + if (pSharedMemory) { + // Create the semaphore + pSemaphore = sem_open(params.semaphore_name, O_CREAT, params.permissions, 0); + + if (pSemaphore == SEM_FAILED) { + sprintf(s, "Creating the semaphore failed; errno is %d", errno); + say(MY_NAME, s); + } + else { + sprintf(s, "the semaphore is %p", (void *)pSemaphore); + say(MY_NAME, s); + + // I seed the shared memory with a random string (the current time). + get_current_time(s); + + strcpy((char *)pSharedMemory, s); + strcpy(last_message_i_wrote, s); + + sprintf(s, "Wrote %zu characters: %s", strlen(last_message_i_wrote), last_message_i_wrote); + say(MY_NAME, s); + + i = 0; + while (!done) { + sprintf(s, "iteration %d", i); + say(MY_NAME, s); + + // Release the semaphore... + rc = release_semaphore(MY_NAME, pSemaphore, params.live_dangerously); + // ...and wait for it to become available again. In real code + // I might want to sleep briefly before calling .acquire() in + // order to politely give other processes an opportunity to grab + // the semaphore while it is free so as to avoid starvation. But + // this code is meant to be a stress test that maximizes the + // opportunity for shared memory corruption and politeness is + // not helpful in stress tests. + if (!rc) + rc = acquire_semaphore(MY_NAME, pSemaphore, params.live_dangerously); + + if (rc) + done = 1; + else { + // I keep checking the shared memory until something new has + // been written. + while ( (!rc) && \ + (!strcmp((char *)pSharedMemory, last_message_i_wrote)) + ) { + // Nothing new; give Mrs. Conclusion another change to respond. + sprintf(s, "Read %zu characters '%s'", strlen((char *)pSharedMemory), (char *)pSharedMemory); + say(MY_NAME, s); + rc = release_semaphore(MY_NAME, pSemaphore, params.live_dangerously); + if (!rc) { + rc = acquire_semaphore(MY_NAME, pSemaphore, params.live_dangerously); + } + } + + + if (rc) + done = 1; + else { + // What I read must be the md5 of what I wrote or something's + // gone wrong. + md5ify(last_message_i_wrote, md5ified_message); + + if (strcmp(md5ified_message, (char *)pSharedMemory) == 0) { + // Yes, the message is OK + i++; + if (i == params.iterations) + done = 1; + + // MD5 the reply and write back to Mrs. Conclusion. + md5ify(md5ified_message, md5ified_message); + + sprintf(s, "Writing %zu characters '%s'", strlen(md5ified_message), md5ified_message); + say(MY_NAME, s); + + strcpy((char *)pSharedMemory, md5ified_message); + strcpy((char *)last_message_i_wrote, md5ified_message); + } + else { + sprintf(s, "Shared memory corruption after %d iterations.", i); + say(MY_NAME, s); + sprintf(s, "Mismatch; new message is '%s', expected '%s'.", (char *)pSharedMemory, md5ified_message); + say(MY_NAME, s); + done = 1; + } + } + } + } + + // Announce for one last time that the semaphore is free again so that + // Mrs. Conclusion can exit. + say(MY_NAME, "Final release of the semaphore followed by a 5 second pause"); + rc = release_semaphore(MY_NAME, pSemaphore, params.live_dangerously); + sleep(5); + // ...before beginning to wait until it is free again. + // Technically, this is bad practice. It's possible that on a + // heavily loaded machine, Mrs. Conclusion wouldn't get a chance + // to acquire the semaphore. There really ought to be a loop here + // that waits for some sort of goodbye message but for purposes of + // simplicity I'm skipping that. + + say(MY_NAME, "Final wait to acquire the semaphore"); + rc = acquire_semaphore(MY_NAME, pSemaphore, params.live_dangerously); + if (!rc) { + say(MY_NAME, "Destroying the shared memory."); + + // Un-mmap the memory... + rc = munmap(pSharedMemory, (size_t)params.size); + if (rc) { + sprintf(s, "Unmapping the memory failed; errno is %d", errno); + say(MY_NAME, s); + } + + // ...close the file descriptor... + if (-1 == close(fd)) { + sprintf(s, "Closing the memory's file descriptor failed; errno is %d", errno); + say(MY_NAME, s); + } + + // ...and destroy the shared memory. + rc = shm_unlink(params.shared_memory_name); + if (rc) { + sprintf(s, "Unlinking the memory failed; errno is %d", errno); + say(MY_NAME, s); + } + } + } + + say(MY_NAME, "Destroying the semaphore."); + // Clean up the semaphore + rc = sem_close(pSemaphore); + if (rc) { + sprintf(s, "Closing the semaphore failed; errno is %d", errno); + say(MY_NAME, s); + } + rc = sem_unlink(params.semaphore_name); + if (rc) { + sprintf(s, "Unlinking the semaphore failed; errno is %d", errno); + say(MY_NAME, s); + } + } + return 0; +} + + +void get_current_time(char *s) { + time_t the_time; + struct tm *the_localtime; + char *pAscTime; + + the_time = time(NULL); + the_localtime = localtime(&the_time); + pAscTime = asctime(the_localtime); + + strcpy(s, pAscTime); +} diff --git a/demo/premise.py b/demo/premise.py new file mode 100644 index 0000000..55711e0 --- /dev/null +++ b/demo/premise.py @@ -0,0 +1,118 @@ +# Python modules +import time +import mmap +import os +import sys +PY_MAJOR_VERSION = sys.version_info[0] +# hashlib is only available in Python >= 2.5. I still want to support +# older Pythons so I import md5 if hashlib is not available. Fortunately +# md5 can masquerade as hashlib for my purposes. +try: + import hashlib +except ImportError: + import md5 as hashlib + +# 3rd party modules +import posix_ipc + +# Utils for this demo +import utils + + +utils.say("Oooo 'ello, I'm Mrs. Premise!") + +params = utils.read_params() + +# Create the shared memory and the semaphore. +memory = posix_ipc.SharedMemory(params["SHARED_MEMORY_NAME"], posix_ipc.O_CREX, + size=params["SHM_SIZE"]) +semaphore = posix_ipc.Semaphore(params["SEMAPHORE_NAME"], posix_ipc.O_CREX) + +# MMap the shared memory +mapfile = mmap.mmap(memory.fd, memory.size) + +# Once I've mmapped the file descriptor, I can close it without +# interfering with the mmap. +memory.close_fd() + +# I seed the shared memory with a random string (the current time). +what_i_wrote = time.asctime() +utils.write_to_memory(mapfile, what_i_wrote) + +for i in range(params["ITERATIONS"]): + utils.say("iteration %d" % i) + if not params["LIVE_DANGEROUSLY"]: + # Release the semaphore... + utils.say("Releasing the semaphore") + semaphore.release() + # ...and wait for it to become available again. In real code + # I might want to sleep briefly before calling .acquire() in + # order to politely give other processes an opportunity to grab + # the semaphore while it is free so as to avoid starvation. But + # this code is meant to be a stress test that maximizes the + # opportunity for shared memory corruption and politeness is + # not helpful in stress tests. + utils.say("Waiting to acquire the semaphore") + semaphore.acquire() + + s = utils.read_from_memory(mapfile) + + # I keep checking the shared memory until something new has + # been written. + while s == what_i_wrote: + # Nothing new; give Mrs. Conclusion another chance to respond. + if not params["LIVE_DANGEROUSLY"]: + utils.say("Releasing the semaphore") + semaphore.release() + utils.say("Waiting to acquire the semaphore") + semaphore.acquire() + + s = utils.read_from_memory(mapfile) + + # What I read must be the md5 of what I wrote or something's + # gone wrong. + if PY_MAJOR_VERSION > 2: + what_i_wrote = what_i_wrote.encode() + + try: + assert(s == hashlib.md5(what_i_wrote).hexdigest()) + except AssertionError: + utils.raise_error(AssertionError, + "Shared memory corruption after %d iterations." % i) + + # MD5 the reply and write back to Mrs. Conclusion. + if PY_MAJOR_VERSION > 2: + s = s.encode() + what_i_wrote = hashlib.md5(s).hexdigest() + utils.write_to_memory(mapfile, what_i_wrote) + +utils.say("") +utils.say("%d iterations complete" % (i + 1)) + +# Announce for one last time that the semaphore is free again so that +# Mrs. Conclusion can exit. +if not params["LIVE_DANGEROUSLY"]: + utils.say("") + utils.say("Final release of the semaphore followed by a 5 second pause") + semaphore.release() + time.sleep(5) + # ...before beginning to wait until it is free again. + # Technically, this is bad practice. It's possible that on a + # heavily loaded machine, Mrs. Conclusion wouldn't get a chance + # to acquire the semaphore. There really ought to be a loop here + # that waits for some sort of goodbye message but for purposes of + # simplicity I'm skipping that. + utils.say("Final wait to acquire the semaphore") + semaphore.acquire() + +utils.say("Destroying semaphore and shared memory.") +mapfile.close() +# I could call memory.unlink() here but in order to demonstrate +# unlinking at the module level I'll do it that way. +posix_ipc.unlink_shared_memory(params["SHARED_MEMORY_NAME"]) + +semaphore.release() + +# I could also unlink the semaphore by calling +# posix_ipc.unlink_semaphore() but I'll do it this way instead. +semaphore.unlink() diff --git a/demo/utils.c b/demo/utils.c new file mode 100644 index 0000000..e9682a4 --- /dev/null +++ b/demo/utils.c @@ -0,0 +1,119 @@ +#include <time.h> +#include <stdlib.h> +#include <stdio.h> +#include <unistd.h> +#include <errno.h> +#include <semaphore.h> +#include <string.h> + +#include "utils.h" +#include "md5.h" + + +void md5ify(char *inString, char *outString) { + md5_state_t state; + md5_byte_t digest[16]; + int i; + + md5_init(&state); + md5_append(&state, (const md5_byte_t *)inString, strlen(inString)); + md5_finish(&state, digest); + + for (i = 0; i < 16; i++) + sprintf(&outString[i * 2], "%02x", digest[i]); +} + +void say(const char *pName, char *pMessage) { + time_t the_time; + struct tm *the_localtime; + char timestamp[256]; + + the_time = time(NULL); + + the_localtime = localtime(&the_time); + + strftime(timestamp, 255, "%H:%M:%S", the_localtime); + + printf("%s @ %s: %s\n", pName, timestamp, pMessage); + +} + + +int release_semaphore(const char *pName, sem_t *pSemaphore, int live_dangerously) { + int rc = 0; + char s[1024]; + + say(pName, "Releasing the semaphore."); + + if (!live_dangerously) { + rc = sem_post(pSemaphore); + if (rc) { + sprintf(s, "Releasing the semaphore failed; errno is %d\n", errno); + say(pName, s); + } + } + + return rc; +} + + +int acquire_semaphore(const char *pName, sem_t *pSemaphore, int live_dangerously) { + int rc = 0; + char s[1024]; + + say(pName, "Waiting to acquire the semaphore."); + + if (!live_dangerously) { + rc = sem_wait(pSemaphore); + if (rc) { + sprintf(s, "Acquiring the semaphore failed; errno is %d\n", errno); + say(pName, s); + } + } + + return rc; +} + + +void read_params(struct param_struct *params) { + char line[1024]; + char name[1024]; + char value[1024]; + + FILE *fp; + + fp = fopen("params.txt", "r"); + + while (fgets(line, 1024, fp)) { + if (strlen(line) && ('#' == line[0])) + ; // comment in input, ignore + else { + sscanf(line, "%[ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghjiklmnopqrstuvwxyz]=%s\n", name, value); + + // printf("name = %s, value = %d\n", name, value); + + if (!strcmp(name, "ITERATIONS")) + params->iterations = atoi(value); + if (!strcmp(name, "LIVE_DANGEROUSLY")) + params->live_dangerously = atoi(value); + if (!strcmp(name, "SEMAPHORE_NAME")) + strcpy(params->semaphore_name, value); + if (!strcmp(name, "SHARED_MEMORY_NAME")) + strcpy(params->shared_memory_name, value); + if (!strcmp(name, "PERMISSIONS")) + params->permissions = (int)strtol(value, NULL, 8); + if (!strcmp(name, "SHM_SIZE")) + params->size = atoi(value); + + name[0] = '\0'; + value[0] = '\0'; + } + } + + printf("iterations = %d\n", params->iterations); + printf("danger = %d\n", params->live_dangerously); + printf("semaphore name = %s\n", params->semaphore_name); + printf("shared memory name = %s\n", params->shared_memory_name); + printf("permissions = %o\n", params->permissions); + printf("size = %d\n", params->size); +} diff --git a/demo/utils.h b/demo/utils.h new file mode 100644 index 0000000..48d083b --- /dev/null +++ b/demo/utils.h @@ -0,0 +1,18 @@ +struct param_struct { + int iterations; + int live_dangerously; + char semaphore_name[512]; + char shared_memory_name[512]; + int permissions; + int size; +}; + + +void md5ify(char *, char *); +void say(const char *, char *); +int acquire_semaphore(const char *, sem_t *, int); +int release_semaphore(const char *, sem_t *, int); +void read_params(struct param_struct *); + + + diff --git a/demo/utils.py b/demo/utils.py new file mode 100644 index 0000000..03b1b3a --- /dev/null +++ b/demo/utils.py @@ -0,0 +1,90 @@ +import time +import sys + +PY_MAJOR_VERSION = sys.version_info[0] + +if PY_MAJOR_VERSION > 2: + NULL_CHAR = 0 +else: + NULL_CHAR = '\0' + +def raise_error(error, message): + # I have to exec() this code because the Python 2 syntax is invalid + # under Python 3 and vice-versa. + s = "raise " + s += "error, message" if (PY_MAJOR_VERSION == 2) else "error(message)" + + exec(s) + + +def say(s): + """Prints a timestamped, self-identified message""" + who = sys.argv[0] + if who.endswith(".py"): + who = who[:-3] + + s = "%s@%1.6f: %s" % (who, time.time(), s) + print (s) + + +def write_to_memory(mapfile, s): + """Writes the string s to the mapfile""" + say("writing %s " % s) + mapfile.seek(0) + # I append a trailing NULL in case I'm communicating with a C program. + s += '\0' + if PY_MAJOR_VERSION > 2: + s = s.encode() + mapfile.write(s) + + +def read_from_memory(mapfile): + """Reads a string from the mapfile and returns that string""" + mapfile.seek(0) + s = [ ] + c = mapfile.read_byte() + while c != NULL_CHAR: + s.append(c) + c = mapfile.read_byte() + + if PY_MAJOR_VERSION > 2: + s = [chr(c) for c in s] + s = ''.join(s) + + say("read %s" % s) + + return s + + +def read_params(): + """Reads the contents of params.txt and returns them as a dict""" + params = { } + + f = open("params.txt") + + for line in f: + line = line.strip() + if line: + if line.startswith('#'): + pass # comment in input, ignore + else: + name, value = line.split('=') + name = name.upper().strip() + + if name == "PERMISSIONS": + # Think octal, young man! + value = int(value, 8) + elif "NAME" in name: + # This is a string; leave it alone. + pass + else: + value = int(value) + + #print "name = %s, value = %d" % (name, value) + + params[name] = value + + f.close() + + return params + |
