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• Computer Networks UNISA - Chap 8 &ndash; Wireless Networking

  - by MarkPearl

  After reading this section you should be able to Explain how nodes exchange wireless signals Identify potential obstacles to successful transmission and their repercussions, such as interference and reflection Understand WLAN architecture Specify the characteristics of popular WLAN transmission methods including 802.11 a/b/g/n Install and configure wireless access points and their clients Describe wireless MAN and WAN technologies, including 802.16 and satellite communications The Wireless Spectrum All wireless signals are carried through the air by electromagnetic waves. The wireless spectrum is a continuum of the electromagnetic waves used for data and voice communication. The wireless spectrum falls between 9KHZ and 300 GHZ. Characteristics of Wireless Transmission Antennas Each type of wireless service requires an antenna specifically designed for that service. The service’s specification determine the antenna’s power output, frequency, and radiation pattern. A directional antenna issues wireless signals along a single direction. An omnidirectional antenna issues and receives wireless signals with equal strength and clarity in all directions The geographical area that an antenna or wireless system can reach is known as its range Signal Propagation LOS (line of sight) uses the least amount of energy and results in the reception of the clearest possible signal. When there is an obstacle in the way, the signal may… pass through the object or be obsrobed by the object or may be subject to reflection, diffraction or scattering. Reflection – waves encounter an object and bounces off it. Diffraction – signal splits into secondary waves when it encounters an obstruction Scattering – is the diffusion or the reflection in multiple different directions of a signal Signal Degradation Fading occurs as a signal hits various objects. Because of fading, the strength of the signal that reaches the receiver is lower than the transmitted signal strength. The further a signal moves from its source, the weaker it gets (this is called attenuation) Signals are also affected by noise – the electromagnetic interference) Interference can distort and weaken a wireless signal in the same way that noise distorts and weakens a wired signal. Frequency Ranges Older wireless devices used the 2.4 GHZ band to send and receive signals. This had 11 communication channels that are unlicensed. Newer wireless devices can also use the 5 GHZ band which has 24 unlicensed bands Narrowband, Broadband, and Spread Spectrum Signals Narrowband – a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies Broadband – uses a relatively wide band of the wireless spectrum and offers higher throughputs than narrowband technologies The use of multiple frequencies to transmit a signal is known as spread-spectrum technology. In other words a signal never stays continuously within one frequency range during its transmission. One specific implementation of spread spectrum is FHSS (frequency hoping spread spectrum). Another type is known as DSS (direct sequence spread spectrum) Fixed vs. Mobile Each type of wireless communication falls into one of two categories Fixed – the location of the transmitted and receiver do not move (results in energy saved because weaker signal strength is possible with directional antennas) Mobile – the location can change WLAN (Wireless LAN) Architecture There are two main types of arrangements Adhoc – data is sent directly between devices – good for small local devices Infrastructure mode – a wireless access point is placed centrally, that all devices connect with 802.11 WLANs The most popular wireless standards used on contemporary LANs are those developed by IEEE’s 802.11 committee. Over the years several distinct standards related to wireless networking have been released. Four of the best known standards are also referred to as Wi-Fi. They are…. 802.11b 802.11a 802.11g 802.11n These four standards share many characteristics. i.e. All 4 use half duplex signalling Follow the same access method Access Method 802.11 standards specify the use of CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to access a shared medium. Using CSMA/CA before a station begins to send data on an 802.11 network, it checks for existing wireless transmissions. If the source node detects no transmission activity on the network, it waits a brief period of time and then sends its transmission. If the source does detect activity, it waits a brief period of time before checking again. The destination node receives the transmission and, after verifying its accuracy, issues an acknowledgement (ACT) packet to the source. If the source receives the ACK it assumes the transmission was successful, – if it does not receive an ACK it assumes the transmission failed and sends it again. Association Two types of scanning… Active – station transmits a special frame, known as a prove, on all available channels within its frequency range. When an access point finds the probe frame, it issues a probe response. Passive – wireless station listens on all channels within its frequency range for a special signal, known as a beacon frame, issued from an access point – the beacon frame contains information necessary to connect to the point. Re-association occurs when a mobile user moves out of one access point’s range and into the range of another. Frames Read page 378 – 381 about frames and specific 802.11 protocols Bluetooth Networks Sony Ericson originally invented the Bluetooth technology in the early 1990s. In 1998 other manufacturers joined Ericsson in the Special Interest Group (SIG) whose aim was to refine and standardize the technology. Bluetooth was designed to be used on small networks composed of personal communications devices. It has become popular wireless technology for communicating among cellular telephones, phone headsets, etc. Wireless WANs and Internet Access Refer to pages 396 – 402 of the textbook for details.

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• Memory leak problem. iPhone SDK

  - by user326375

  Hello, i've got a problem, i cannot solve it, just recieving error: Program received signal: “0”. The Debugger has exited due to signal 10 (SIGBUS).The Debugger has exited due to signal 10 (SIGBUS). Here is some method, if i comment it out, problem goes aways - (void)loadTexture { const int num_tex = 10; glGenTextures(num_tex, &textures[0]); //TEXTURE #1 textureImage[0] = [UIImage imageNamed:@"wonder.jpg"].CGImage; //TEXTURE #2 textureImage[1] = [UIImage imageNamed:@"wonder.jpg"].CGImage; //TEXTURE #3 textureImage[2] = [UIImage imageNamed:@"wall_eyes.jpg"].CGImage; //TEXTURE #4 textureImage[3] = [UIImage imageNamed:@"wall.jpg"].CGImage; //TEXTURE #5 textureImage[4] = [UIImage imageNamed:@"books.jpg"].CGImage; //TEXTURE #6 textureImage[5] = [UIImage imageNamed:@"bush.jpg"].CGImage; //TEXTURE #7 textureImage[6] = [UIImage imageNamed:@"mushroom.jpg"].CGImage; //TEXTURE #8 textureImage[7] = [UIImage imageNamed:@"roots.jpg"].CGImage; //TEXTURE #9 textureImage[8] = [UIImage imageNamed:@"roots.jpg"].CGImage; //TEXTURE #10 textureImage[9] = [UIImage imageNamed:@"clean.jpg"].CGImage; for(int i=0; i<num_tex; i++) { NSInteger texWidth = CGImageGetWidth(textureImage[i]); NSInteger texHeight = CGImageGetHeight(textureImage[i]); GLubyte *textureData = (GLubyte *)malloc(texWidth * texHeight * 4); CGContextRef textureContext = CGBitmapContextCreate(textureData, texWidth, texHeight, 8, texWidth * 4, CGImageGetColorSpace(textureImage[i]), kCGImageAlphaPremultipliedLast); CGContextDrawImage(textureContext, CGRectMake(0.0, 0.0, (float)texWidth, (float)texHeight), textureImage[i]); CGContextRelease(textureContext); glBindTexture(GL_TEXTURE_2D, textures[i]); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, texWidth, texHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, textureData); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); free(textureData); } } anyone can help me with releasing/deleting objects in this method? Thanks.

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• Improve wireless performance

  - by djechelon

  Hello, I have a Trust Speedshare Turbo Pro router, which is running on channel 6. I found that the wireless signal (and network performance) dramatically drops from my PDA (I can barely attach to the network, even if I set the PDA's energy settings to maximum wireless performance) when I even exit my room, and I don't have shielded walls or something like that. I can't even stream a SD video from my desktop (connected via LAN) to my laptop using WiFi, while via LAN it works fine. I read that changing router's channel could improve performance due to interference reducing. I found that almost all wireless networks around here run on channels 6 and 11. I tried to go to my router's settings page to change channel, but I found that the combo box only allows me to select 6!! I'm not sure, but I may have been able in the past to change channel, though not to all of the available channels. A few minutes ago I tried a firmware upgrade, but it didn't solve my problem. My question is Is it possible that my router is someway locked to its channel? I bought it on my own, I didn't receive it from my ISP Apart from boosting the antenna power to the maximum (which, by the way, increases the EM radiation my and my family's bodies absorb 24/7 and is little more environment-unfriendly), do you have any tips on getting high quality transmission up to 5 metres from the antenna? Thank you

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• how to clear stack after stack overflow signal occur

  - by user353573

  In pthread, After reaching yellow zone in stack, signal handler stop the recursive function by making it return however, we can only continue to use extra area in yellow zone, how to clear the rubbish before the yellow zone in the thread stack ? (Copied from "answers"): #include <pthread.h> #include <stdio.h> #include <stdlib.h> #include <signal.h> #include <setjmp.h> #include <sys/mman.h> #include <unistd.h> #include <assert.h> #include <sys/resource.h> #define ALT_STACK_SIZE (64*1024) #define YELLOW_ZONE_PAGES (1) typedef struct { size_t stack_size; char* stack_pointer; char* red_zone_boundary; char* yellow_zone_boundary; sigjmp_buf return_point; size_t red_zone_size; } ThreadInfo; static pthread_key_t thread_info_key; static struct sigaction newAct, oldAct; bool gofromyellow = false; int call_times = 0; static void main_routine(){ // make it overflow if(gofromyellow == true) { printf("return from yellow zone, called %d times\n", call_times); return; } else { call_times = call_times + 1; main_routine(); gofromyellow = true; } } // red zone management static void stackoverflow_routine(){ fprintf(stderr, "stack overflow error.\n"); fflush(stderr); } // yellow zone management static void yellow_zone_hook(){ fprintf(stderr, "exceed yellow zone.\n"); fflush(stderr); } static int get_stack_info(void** stackaddr, size_t* stacksize){ int ret = -1; pthread_attr_t attr; pthread_attr_init(&attr); if(pthread_getattr_np(pthread_self(), &attr) == 0){ ret = pthread_attr_getstack(&attr, stackaddr, stacksize); } pthread_attr_destroy(&attr); return ret; } static int is_in_stack(const ThreadInfo* tinfo, char* pointer){ return (tinfo->stack_pointer <= pointer) && (pointer < tinfo->stack_pointer + tinfo->stack_size); } static int is_in_red_zone(const ThreadInfo* tinfo, char* pointer){ if(tinfo->red_zone_boundary){ return (tinfo->stack_pointer <= pointer) && (pointer < tinfo->red_zone_boundary); } } static int is_in_yellow_zone(const ThreadInfo* tinfo, char* pointer){ if(tinfo->yellow_zone_boundary){ return (tinfo->red_zone_boundary <= pointer) && (pointer < tinfo->yellow_zone_boundary); } } static void set_yellow_zone(ThreadInfo* tinfo){ int pagesize = sysconf(_SC_PAGE_SIZE); assert(pagesize > 0); tinfo->yellow_zone_boundary = tinfo->red_zone_boundary + pagesize * YELLOW_ZONE_PAGES; mprotect(tinfo->red_zone_boundary, pagesize * YELLOW_ZONE_PAGES, PROT_NONE); } static void reset_yellow_zone(ThreadInfo* tinfo){ size_t pagesize = tinfo->yellow_zone_boundary - tinfo->red_zone_boundary; if(mmap(tinfo->red_zone_boundary, pagesize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0) == 0){ perror("mmap failed"), exit(1); } mprotect(tinfo->red_zone_boundary, pagesize, PROT_READ | PROT_WRITE); tinfo->yellow_zone_boundary = 0; } static void signal_handler(int sig, siginfo_t* sig_info, void* sig_data){ if(sig == SIGSEGV){ ThreadInfo* tinfo = (ThreadInfo*) pthread_getspecific(thread_info_key); char* fault_address = (char*) sig_info->si_addr; if(is_in_stack(tinfo, fault_address)){ if(is_in_red_zone(tinfo, fault_address)){ siglongjmp(tinfo->return_point, 1); }else if(is_in_yellow_zone(tinfo, fault_address)){ reset_yellow_zone(tinfo); yellow_zone_hook(); gofromyellow = true; return; } else { //inside stack not related overflow SEGV happen } } } } static void register_application_info(){ pthread_key_create(&thread_info_key, NULL); sigemptyset(&newAct.sa_mask); sigaddset(&newAct.sa_mask, SIGSEGV); newAct.sa_sigaction = signal_handler; newAct.sa_flags = SA_SIGINFO | SA_RESTART | SA_ONSTACK; sigaction(SIGSEGV, &newAct, &oldAct); } static void register_thread_info(ThreadInfo* tinfo){ stack_t ss; pthread_setspecific(thread_info_key, tinfo); get_stack_info((void**)&tinfo->stack_pointer, &tinfo->stack_size); printf("stack size %d mb\n", tinfo->stack_size/1024/1024 ); tinfo->red_zone_boundary = tinfo->stack_pointer + tinfo->red_zone_size; set_yellow_zone(tinfo); ss.ss_sp = (char*)malloc(ALT_STACK_SIZE); ss.ss_size = ALT_STACK_SIZE; ss.ss_flags = 0; sigaltstack(&ss, NULL); } static void* thread_routine(void* p){ ThreadInfo* tinfo = (ThreadInfo*)p; register_thread_info(tinfo); if(sigsetjmp(tinfo->return_point, 1) == 0){ main_routine(); } else { stackoverflow_routine(); } free(tinfo); printf("after tinfo, end thread\n"); return 0; } int main(int argc, char** argv){ register_application_info(); if( argc == 2 ){ int stacksize = atoi(argv[1]); pthread_attr_t attr; pthread_attr_init(&attr); pthread_attr_setstacksize(&attr, 1024 * 1024 * stacksize); { pthread_t pid0; ThreadInfo* tinfo = (ThreadInfo*)calloc(1, sizeof(ThreadInfo)); pthread_attr_getguardsize(&attr, &tinfo->red_zone_size); pthread_create(&pid0, &attr, thread_routine, tinfo); pthread_join(pid0, NULL); } } else { printf("Usage: %s stacksize(mb)\n", argv[0]); } return 0; } C language in linux, ubuntu

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• MPI signal handling

  - by Seth Johnson

  When using mpirun, is it possible to catch signals (for example, the SIGINT generated by ^C) in the code being run? For example, I'm running a parallelized python code. I can except KeyboardInterrupt to catch those errors when running python blah.py by itself, but I can't when doing mpirun -np 1 python blah.py. Does anyone have a suggestion? Even finding how to catch signals in a C or C++ compiled program would be a helpful start. If I send a signal to the spawned Python processes, they can handle the signals properly; however, signals sent to the parent orterun process (i.e. from exceeding wall time on a cluster, or pressing control-C in a terminal) will kill everything immediately.

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• wxPython: Sending a signal to several widgets

  - by cool-RR

  I am not even sure how to ask this question. I want something that is like the wxPython event system, but a bit different. I'll try to explain. When there is a certain change in my program (a "tree change", never mind what that is,) I want to send a signal to all the widgets in my program, notifying them that a "tree change" has occurred, and they should change their display in response. How do I do this? It sounds a little bit like wxPython events, but not really, since events don't spread to all widgets, as far as I know. What would be a good way to do this?

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• How to properly siglongjmp out of signal handler?

  - by EpsilonVector

  Suppose I have the following code: In order to implement a context switch I activate ualarm and when it jumps to the handler it setjmp's the current context, and longjmps to the next, expecting to eventually return to the alarm handler and longjmped back into this context (the contexts are cycled through in a Round Robin). For this I need to keep SIGALRM unblocked in between alarm_handlers. I came up with the following code, which doesn't seem to work. What's wrong with it and what is the right way to do this? void alarm_handler(){ if(sigsetjmp(toc->threads[toc->RR_pointer].env, 0)){ ualarm(200, 0); signal(SIGALRM, alarm_handler); return; } get_next_context_number(toc->RR_pointer); //is a macro for (j=0; j<10; j++) printf("ALARM HANDLER\n"); siglongjmp(toc->threads[toc->RR_pointer].env, 1); }

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• Ruby Multithreading: making one thread wait for a signal from another

  - by Peter

  In Ruby, I want to have two threads running at the same time, and want the background thread to periodically signal the foreground thread. How do I get the foreground thread to block until the background thread says 'go'? I can think of a few ways to do it, but am after the most appropriate, idiomatic Ruby method. In code: loop do # background, thread 1 sleep 3 receive_input # tell foreground input is ready # <-- how do I do this? end and loop do # foreground, thread 2 wait_for_signal_from_background # <-- how do I do this? do_something end

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• PHP getting blank pages after submit a form + signal Segmentation fault (11)

  - by Ole Media

  I few days ago I update my macbook pro to snow leopard, and since then some php files are not showing. This is what happens: I created a php form, when going to 'http://localhost/webform.php' I can see the form just fine. Then, once I submit the form, I just get a blank page. I enable error and warnings reporting under php.ini to make sure I'm not missing something, but still I'm not getting anything, just the blank page. Then I checked under apache log files, and what I notice is that every time I submit the form I see the following line coming up under the apache logs: [Wed Apr 07 21:40:28 2010] [notice] child pid 70223 exit signal Segmentation fault (11) I'm clueless on this one. Any ideas on how to fix it?

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• Signal "0" error while scrolling a tableview with images

  - by Amitkumar

  Hi, I have a problem while scrolling images on tableview. I am getting a Signal "0" error. I think it is due to some memory issues but I am not able to find out the exact error. The code is as follows, - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [travelSummeryPhotosTable dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier]autorelease]; } //Photo ImageView UIImageView *photoTag = [[UIImageView alloc] initWithFrame:CGRectMake(5.0, 5.0, 85.0, 85.0)]; NSString *rowPath =[[imagePathsDictionary valueForKey:[summaryTableViewDataArray objectAtIndex:indexPath.section]] objectAtIndex:indexPath.row]; photoTag.image = [UIImage imageWithContentsOfFile:rowPath]; [cell.contentView addSubview:photoTag]; [photoTag release]; // Image Caption UILabel *labelImageCaption = [[UILabel alloc] initWithFrame:CGRectMake(110.0, 15.0, 190.0, 50.0)]; labelImageCaption.textAlignment = UITextAlignmentLeft; NSString *imageCaptionText =[ [imageCaptionsDictionary valueForKey:[summaryTableViewDataArray objectAtIndex:indexPath.section]] objectAtIndex:indexPath.row]; labelImageCaption.text = imageCaptionText; [cell.contentView addSubview:labelImageCaption]; [labelImageCaption release]; return cell; } Thanks in advance.

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• iPhone OpenGLES: Textures are consuming too much memory and the program crashes with signal "0"

  - by CustomAppsMan

  I am not sure what the problem is. My app is running fine on the simulator but when I try to run it on the iPhone it crashes during debugging or without debugging with signal "0". I am using the Texture2D.m and OpenGLES2DView.m from the examples provided by Apple. I profiled the app on the iPhone with Instruments using the Memory tracer from the Library and when the app died the final memory consumed was about 60Mb real and 90+Mb virtual. Is there some other problem or is the iPhone just killing the application because it has consumed too much memory? If you need any information please state it and I will try to provide it. I am creating thousands of textures at load time which is why the memory consumption is so high. Really cant do anything about reducing the number of pics being loaded. I was running before on just UIImage but it was giving me really low frame rates. I read on this site that I should use OpenGLES for higher frame rates. Also sub question is there any way not to use UIImage to load the png file and then use the Texture class provided to create the texture for OpenGLES functions to use it for drawing? Is there some function in OpenGLES which will create a texture straight from a png file?

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• receiving signal: EXC_BAD_ACCESS in web service call function

  - by murali

  I'm new to iPhone development. I'm using xcode 4.2. When I click on the save button, I'm getting values from the html page and my web service is processing them, and then I get the error: program received signal: EXC_BAD_ACCESS in my web service call function. Here is my code: NSString *val=[WebviewObj stringByEvaluatingJavaScriptFromString:@"save()"]; NSLog(@"return value:: %@",val); [adict setObject:[NSString stringWithFormat:@"%i",userid5] forKey:@"iUser_Id" ]; [adict setObject:[[val componentsSeparatedByString:@","]objectAtIndex:0] forKey:@"vImage_Url"]; [adict setObject:[[val componentsSeparatedByString:@","]objectAtIndex:1] forKey:@"IGenre_Id"]; [adict setObject:[[val componentsSeparatedByString:@","]objectAtIndex:2] forKey:@"vTrack_Name"]; [adict setObject:[[val componentsSeparatedByString:@","]objectAtIndex:3] forKey:@"vAlbum_Name"]; [adict setObject:[[val componentsSeparatedByString:@","]objectAtIndex:4] forKey:@"vMusic_Url"]; [adict setObject:[[val componentsSeparatedByString:@","]objectAtIndex:5] forKey:@"iTrack_Duration_min"]; [adict setObject:[[val componentsSeparatedByString:@","]objectAtIndex:6] forKey:@"iTrack_Duration_sec"]; [adict setObject:[[val componentsSeparatedByString:@","]objectAtIndex:7] forKey:@"vDescription"]; NSLog(@"dict==%@",[adict description]); NSString *URL2= @"http://184.164.156.55/Music/Track.asmx/AddTrack"; obj=[[UrlController alloc]init]; obj.URL=URL2; obj.InputParameters = adict; [obj WebserviceCall]; obj.delegate= self; //this is my function..it is working for so many function calls -(void)WebserviceCall{ webData = [[NSMutableData alloc] init]; NSMutableURLRequest *urlRequest = [[ NSMutableURLRequest alloc ] initWithURL: [ NSURL URLWithString: URL ] ]; NSString *httpBody = @""; for(id key in InputParameters) { if([httpBody length] == 0){ httpBody=[httpBody stringByAppendingFormat:@"&%@=%@",key,[InputParameters valueForKey:key]]; } else{ httpBody=[httpBody stringByAppendingFormat:@"&%@=%@",key,[InputParameters valueForKey:key]]; } } httpBody = [httpBody stringByAppendingFormat:httpBody];//Here i am getting EXC_BAD_ACCESS [urlRequest setHTTPMethod: @"POST" ]; [urlRequest setHTTPBody:[httpBody dataUsingEncoding:NSUTF8StringEncoding]]; [urlRequest setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"content-type"]; NSURLConnection *theConnection = [[NSURLConnection alloc] initWithRequest:urlRequest delegate:self]; } Can any one help me please? thanks in advance

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• Problem with signal handlers being called too many times [closed]

  - by Hristo

  how can something print 3 times when it only goes the printing code twice? I'm coding in C and the code is in a SIGCHLD signal handler I created. void chld_signalHandler() { int pidadf = (int) getpid(); printf("pidafdfaddf: %d\n", pidadf); while (1) { int termChildPID = waitpid(-1, NULL, WNOHANG); if (termChildPID == 0 || termChildPID == -1) { break; } dll_node_t *temp = head; while (temp != NULL) { printf("stuff\n"); if (temp->pid == termChildPID && temp->type == WORK) { printf("inside if\n"); // read memory mapped file b/w WORKER and MAIN // get statistics and write results to pipe char resultString[256]; // printing TIME int i; for (i = 0; i < 24; i++) { sprintf(resultString, "TIME; %d ; %d ; %d ; %s\n",i,1,2,temp->stats->mboxFileName); fwrite(resultString, strlen(resultString), 1, pipeFD); } remove_node(temp); break; } temp = temp->next; } printf("done printing from sigchld \n"); } return; } the output for my MAIN process is this: MAIN PROCESS 16214 created WORKER PROCESS 16220 for file class.sp10.cs241.mbox pidafdfaddf: 16214 stuff stuff inside if done printing from sigchld MAIN PROCESS 16214 created WORKER PROCESS 16221 for file class.sp10.cs225.mbox pidafdfaddf: 16214 stuff stuff inside if done printing from sigchld and the output for the MONITOR process is this: MONITOR: pipe is open for reading MONITOR PIPE: TIME; 0 ; 1 ; 2 ; class.sp10.cs225.mbox MONITOR PIPE: TIME; 0 ; 1 ; 2 ; class.sp10.cs225.mbox MONITOR PIPE: TIME; 0 ; 1 ; 2 ; class.sp10.cs241.mbox MONITOR: end of readpipe ( I've taken out repeating lines so I don't take up so much space ) Thanks, Hristo

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• Problem with signal handlers

  - by Hristo

  how can something print 3 times when it only goes the printing code twice? I'm coding in C and the code is in a SIGCHLD signal handler I created. void chld_signalHandler() { int pidadf = (int) getpid(); printf("pidafdfaddf: %d\n", pidadf); while (1) { int termChildPID = waitpid(-1, NULL, WNOHANG); if (termChildPID == 0 || termChildPID == -1) { break; } dll_node_t *temp = head; while (temp != NULL) { printf("stuff\n"); if (temp->pid == termChildPID && temp->type == WORK) { printf("inside if\n"); // read memory mapped file b/w WORKER and MAIN // get statistics and write results to pipe char resultString[256]; // printing TIME int i; for (i = 0; i < 24; i++) { sprintf(resultString, "TIME; %d ; %d ; %d ; %s\n",i,1,2,temp->stats->mboxFileName); fwrite(resultString, strlen(resultString), 1, pipeFD); } remove_node(temp); break; } temp = temp->next; } printf("done printing from sigchld \n"); } return; } the output for my MAIN process is this: MAIN PROCESS 16214 created WORKER PROCESS 16220 for file class.sp10.cs241.mbox pidafdfaddf: 16214 stuff stuff inside if done printing from sigchld MAIN PROCESS 16214 created WORKER PROCESS 16221 for file class.sp10.cs225.mbox pidafdfaddf: 16214 stuff stuff inside if done printing from sigchld and the output for the MONITOR process is this: MONITOR: pipe is open for reading MONITOR PIPE: TIME; 0 ; 1 ; 2 ; class.sp10.cs225.mbox MONITOR PIPE: TIME; 0 ; 1 ; 2 ; class.sp10.cs225.mbox MONITOR PIPE: TIME; 0 ; 1 ; 2 ; class.sp10.cs241.mbox MONITOR: end of readpipe ( I've taken out repeating lines so I don't take up so much space ) Thanks, Hristo

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• Thread 1: Program received signal:"Sigbart"

  - by user813678

  When i try to run my app on my iPhone, I get " Thread 1: Program received signal:"Sigbart" xCode say that points to [self.navigationController pushViewController:detailViewController animated:YES]; import "RootViewController.h" import "global.h" import "golfbaner.h" @implementation RootViewController @synthesize banenavn; (void)viewDidLoad { [super viewDidLoad]; NSArray *temp = [[NSArray alloc] initWithObjects: @"Alsten Golfklubb", @"Arendal og Omegn Golfklubb", @"Asker Golfklubb", @"Askim Golfklubb", @"Atlungstad Golfklubb", @"Aurskog Golfpark", @"Ballerud Golfklubb", @"Bamble Golfklubb", @"Bergen Golfklubb", @"Bjorli Golfklubb", @"Bjørnefjorden Golfklubb", @"Bjaavann Golfklubb", @"Bodø Golfbane", @"Borre Golfbane", @"Borregaard Golfklubb", @"Brønnøysund Golfklubb", @"Byneset Golfklubb", @"Bærum Golfklubb", @"Drammen Golfklubb", @"Drøbak Golfklubb", @"Egersund Golfklubb", @"Eidskog Golfklubb", @"Eiker Golfklubb", @"Ekholt Golfklubb", @"Elverum Golfklubb", @"Fana Golfklubb", @"Fet Golfklubb", @"Frosta Golfklubb", @"Geilo Golfklubb", @"Giske Golfklubb", @"Gjerdrum Golfpark", @"Gjersjøen Golfklubb", @"Gjøvik og Toten Golfklubb", @"Gran Golfklubb", @"Grenland Golfklubb", @"Grimstad Golfklubb", @"Grini Golfklubb", @"Groruddalen Golfklubb", @"Grønmo Golfklubb", @"Hafjell Golfklubb", @"Haga Golfpark", @"Hakadal Golfklubb", @"Halden Golfklubb", @"Hallingdal Golfklubb", @"Hammerfest og Kvalsund Golfklubb", @"Hardanger Golfklubb", @"Harstad Golfklubb", @"Haugaland Golfklubb", @"Hauger Golf", @"Haugesund Golfklubb", @"Helgeland Golfklubb", @"Hemsedal Golfklubb", @"Herdla Golfklubb", @"Hitra Golfklubb", @"Hof Golfklubb", @"Holtsmark Golfklubb", @"Hovden Golfklubb", @"Hurum Golfklubb", @"Huseby og Hankø Golfklubb", @"Hvaler Golfklubb", @"Hvam Golfklubb", @"Jæren Golfklubb", @"Karasjok Golfklubb", @"Karmøy Golfklubb", @"Kjekstad Golfklubb", @"Klæbu Golfklubb", @"Kongsberg Golfklubb", @"Kongsvinger Golfklubb", @"Kragerø Golfklubb", @"Kristiansand Golfklubb", @"Kristiansund og Omegn Golfklubb", @"Krokhol Golfklubb", @"Kvinesdal og Omegn Golfklubb", @"Kvinnherad Golfklubb", @"Kvitfjell", @"Larvik Golfklubb", @"Lillehammer Golf Park", @"Lillestrøm Golfklubb", @"Lofoten Golf Links", @"Lommedalen Golfklubb", @"Losby Golfklubb", @"Lærdal Golfklubb", @"Lønne Golfklubb", @"Mandal Golfklubb", @"Meland Golfklubb", @"Midt-Troms Golfklubb", @"Miklagard Golfklubb", @"Mjøsen Golfklubb", @"Moa Golfklubb", @"Modum Golfklubb", @"Molde Golfklubb", @"Moss og Rygge Golfklubb", @"Mørk Golfklubb", @"Namdal Golfklubb", @"Namsos Golfklubb", @"Narvik Golfklubb", @"Nes Golfklubb", @"Nittedal Golfklubb", @"Nordfjord Golfklubb", @"Nordvegen Golfklubb", @"Norefjell Golfklubb", @"Norsjø og Omegn Golfklubb", @"North Cape Golf Club", @"Nærøysund Golfklubb", @"Nøtterøy Golfklubb", @"Odda Golfklubb", @"Ogna Golfklubb", @"Onsøy Golfklubb", @"Oppdal Golfklubb", @"Oppegård Golfklubb", @"Oslo Golfklubb", @"Oustøen Country Club", @"Polarsirkelen Golf", @"Preikestolen Golfklubb", @"Randaberg Golfklubb", @"Randsfjorden Golfklubb", @"Rauma Golfklubb", @"Re Golfklubb", @"Ringerike Golfklubb", @"Rygge Flystasjon Golf Club", @"Røros Golfklubb", @"Salten Golfklubb", @"Sandane Golfklubb", @"Sande Golfklubb", @"Sandefjord Golfklubb", @"Sandnes Golfklubb", @"Sauda Golfklubb", @"Selbu Golfklubb", @"Selje Golfklubb", @"Setesdal Golfklubb", @"Skei Golfklubb", @"Ski Golfklubb", @"Skjeberg Golfklubb", @"Smøla Golfklubb", @"Sola Golfklubb", @"Solastranden Golfklubb", @"Solum Golfklubb", @"Soon Golfklubb", @"Sorknes Golfklubb", @"Sotra Golfklubb", @"Stavanger Golfklubb", @"Steinkjer Golfklubb", @"Stiklestad Golfklubb", @"Stjørdal Golfklubb", @"Stord Golfklubb", @"Stranda Golfklubb", @"Stryn Golfklubb", @"Sunndal Golfklubb", @"Sunnfjord Golfklubb", @"Sunnmøre Golfklubb", @"Surnadal Golfklubb", @"Tjøme Golfklubb", @"Tromsø Golfklubb", @"Trondheim Golfklubb", @"Trysil Golfklubb", @"Tyrifjord Golfklubb", @"Ullensaker Golfklubb", @"Valdres Golfklubb", @"Vanylven Golfklubb", @"Varanger Golfklubb", @"Vesterålen Golfklubb", @"Vestfold Golfklubb", @"Vildmarken Golfklubb", @"Volda Golfklubb", @"Voss Golfklubb", @"Vrådal Golfklubb", @"Østmarka Golfklubb", @"Øya Golfpark", @"Ålesund Golfklubb", nil]; self.banenavn = temp; [temp release]; self.title = @"Golfbaner i Norge"; self.navigationController.navigationBar.barStyle = UIBarStyleBlackTranslucent; } (void)viewWillAppear:(BOOL)animated { [super viewWillAppear:animated]; } (void)viewDidAppear:(BOOL)animated { [super viewDidAppear:animated]; } (void)viewWillDisappear:(BOOL)animated { [super viewWillDisappear:animated]; } (void)viewDidDisappear:(BOOL)animated { [super viewDidDisappear:animated]; } /* // Override to allow orientations other than the default portrait orientation. - (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation { // Return YES for supported orientations. return (interfaceOrientation == UIInterfaceOrientationPortrait); } */ // Customize the number of sections in the table view. - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return 1; } (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return [banenavn count]; } // Customize the appearance of table view cells. - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease]; } cell.textLabel.text = [banenavn objectAtIndex:indexPath.row]; return cell; } /* // Override to support conditional editing of the table view. - (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath { // Return NO if you do not want the specified item to be editable. return YES; } */ /* // Override to support editing the table view. - (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath { if (editingStyle == UITableViewCellEditingStyleDelete) { // Delete the row from the data source. [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; } else if (editingStyle == UITableViewCellEditingStyleInsert) { // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view. } } */ /* // Override to support rearranging the table view. - (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath { } */ /* // Override to support conditional rearranging of the table view. - (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath { // Return NO if you do not want the item to be re-orderable. return YES; } */ (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { golf = [banenavn objectAtIndex:indexPath.row]; golfbaner *detailViewController = [[golfbaner alloc] initWithNibName:@"Golfbaner" bundle:nil]; [self.navigationController pushViewController:detailViewController animated:YES]; [detailViewController release]; } (void)didReceiveMemoryWarning { // Releases the view if it doesn't have a superview. [super didReceiveMemoryWarning]; // Relinquish ownership any cached data, images, etc that aren't in use. } (void)viewDidUnload { [super viewDidUnload]; // Relinquish ownership of anything that can be recreated in viewDidLoad or on demand. // For example: self.myOutlet = nil; } (void)dealloc { [super dealloc]; } @end

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• Is this Ubuntu One DBus signal connection code correct?

  - by Chris Wilson

  This is my first time using DBus so I'm not entirely sure if I'm going about this the right way. I'm attempting to connect the the Ubuntu One DBus service and obtain login credentials for my app, however the slots I've connected to the DBus return signals detailed here never seem to be firing, despite a positive result being returned during the connection. Before I start looking for errors in the details relating to this specific service, could someone please tell me if this code would even work in the first place, or if I'm done something wrong here? int main() { UbuntuOneDBus *u1Dbus = new UbuntuOneDBus; if( u1Dbus->init() ){ qDebug() << "Message queued"; } } UbuntuOneDBus::UbuntuOneDBus() { service = "com.ubuntuone.Credentials"; path = "/credentials"; interface = "com.ubuntuone.CredentialsManagement"; method = "register"; signature = "a{ss} (Dict of {String, String})"; connectReturnSignals(); } bool UbuntuOneDBus::init() { QDBusMessage message = QDBusMessage::createMethodCall( service, path, interface, method ); bool queued = QDBusConnection::sessionBus().send( message ); return queued; } void UbuntuOneDBus::connectReturnSignals() { bool connectionSuccessful = false; connectionSuccessful = QDBusConnection::sessionBus().connect( service, path, interface, "CredentialsFound", "a{ss} (Dict of {String, String})", this, SLOT( credentialsFound() ) ); if( ! connectionSuccessful ) qDebug() << "Connection to DBus::CredentialsFound signal failed"; connectionSuccessful = QDBusConnection::systemBus().connect( service, path, interface, "CredentialsNotFound", "(nothing)", this, SLOT( credentialsNotFound() ) ); if( ! connectionSuccessful ) qDebug() << "Connection to DBus::CredentialsNotFound signal failed"; connectionSuccessful = QDBusConnection::systemBus().connect( service, path, interface, "CredentialsError", "a{ss} (Dict of {String, String})", this, SLOT( credential if( ! connectionSuccessful ) qDebug() << "Connection to DBus::CredentialsError signal failed"; } void UbuntuOneDBus::credentialsFound() { std::cout << "Credentials found" << std::endl; } void UbuntuOneDBus::credentialsNotFound() { std::cout << "Credentials not found" << std::endl; } void UbuntuOneDBus::credentialsError() { std::cout << "Credentials error" << std::endl; }

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• With Google DFP (Small Business) is it possible to disable AdSense in an Ad Slot on a per-request basis?

  - by Daniel Pehrson

  Setup: I run a network of websites that target different hobby niches and have a section dedicated to community classifieds. I serve advertising on these sites through Google DFP for Small Business with AdSense enabled on the slots. Problem: One of the next sites in my network will be targeting the firearms/shooting industry and as such the classifieds section will not comply with the prohibited content guidelines of AdSense regarding the sale (or coordination of sale) of weapons. I work very hard to comply with the guidelines of my partners even if I don't understand/agree with them and after talking with many people have decided that the best option is to disable AdSense serving on that section of that website, while leaving it on for the rest of the network. Solution: Right now my only idea for this is to duplicate all my site's ad slots and tack a "_sensitive" onto the end of each one (eg. header and header_sensitive) conditionally registering ad slots based on whether or not I am in the sensitive section of the sensitive site. My hope however is that there may be a way to accomplish this without duplicating all my ad slots possibly with some sort of options to the GA_googleFillSlot() call that allows me to say "load ads from this slot but do not serve AdSense no matter what."

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• Can I ignore a SIGFPE resulting from division by zero?

  - by Mikeage

  I have a program which deliberately performs a divide by zero (and stores the result in a volatile variable) in order to halt in certain circumstances. However, I'd like to be able to disable this halting, without changing the macro that performs the division by zero. Is there any way to ignore it? I've tried using #include <signal.h> ... int main(void) { signal(SIGFPE, SIG_IGN); ... } but it still dies with the message "Floating point exception (core dumped)". I don't actually use the value, so I don't really care what's assigned to the variable; 0, random, undefined... EDIT: I know this is not the most portable, but it's intended for an embedded device which runs on many different OSes. The default halt action is to divide by zero; other platforms require different tricks to force a watchdog induced reboot (such as an infinite loop with interrupts disabled). For a PC (linux) test environment, I wanted to disable the halt on division by zero without relying on things like assert.

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• Externally disabling signals for a Linux program.

  - by Harry

  Hello, On Linux, is it possible to somehow disable signaling for programs externally... that is, without modifying their source code? Context: I'm calling a C (and also a Java) program from within a bash script on Linux. I don't want any interruptions for my bash script, and for the other programs that the script launches (as foreground processes). While I can use a... trap '' INT ... in my bash script to disable the Ctrl C signal, this works only when the program control happens to be in the bash code. That is, if I press Ctrl C while the C program is running, the C program gets interrupted and it exits! This C program is doing some critical operation because of which I don't want it be interrupted. I don't have access to the source code of this C program, so signal handling inside the C program is out of question. #!/bin/bash trap 'echo You pressed Ctrl C' INT # A C program to emulate a real-world, long-running program, # which I don't want to be interrupted, and for which I # don't have the source code! # # File: y.c # To build: gcc -o y y.c # # #include <stdio.h> # int main(int argc, char *argv[]) { # printf("Performing a critical operation...\n"); # for(;;); // Do nothing forever. # printf("Performing a critical operation... done.\n"); # } ./y Regards, /HS

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• Connecting a Wifi router to receivers with a cable instead of antenna?

  - by 31eee384

  This is a very strange question--I'd go so far as to say it's a stupid question. I'm being told that it is possible to, to describe it briefly, use a cable to connect an access point and a receiver directly to one another. This means that I would unscrew the access point's antenna, and attach one end of a cable to the port. Then, on the wireless receiver, I would also unscrew the antenna and plug in the other side of the cable. I'm being told the connection would work after this, just as a normal Wifi connection would. Bonus mini-question: if this works, would it still work if a splitter were attached to the access point and multiple receivers plugged in to the network? What would happen if I do this? Based on my surprisingly deficient knowledge of radio transmission, I don't think it would work. I would like some help knowing why it won't (or will) though, if possible. This is a somewhat hypothetical question--I realize that Ethernet does this exact job very handily, and I could just throw in a switch instead of the splitter. I simply feel that I should understand this scenario. Thanks for any help you can offer.

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• How to disable ^C from being echoed on Linux on Ctrl-C

  - by pts

  When I press Ctrl-C in any pseudoterminal (xterm, gnome-terminal, rxvt, text console and SSH) in Karmic Koala, the string ^C gets echoed to the terminal in Ubuntu Karmic Koala. This hasn't happened in Ubuntu Jaunty Jackalope. I'd like to get rid of the extra ^C. Example: $ cat foo foo ^C $ _ I got the above by typing C, A, T, Enter, F, O, O, Enter, Ctrl-C. I want to get rid of the ^C, and get this for the same keypresses: $ cat foo foo $ _ I tried setting stty -echoctl, which created a single-character HT (or a box with Unicode 0003 in it) instead of the ^C. I want to see absolutely nothing when I press Ctrl-C. I'm using Linux linux 2.6.31-20-generic-pae #57-Ubuntu SMP Mon Feb 8 10:23:59 UTC 2010 i686 GNU/Linux

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• How to make a Shell Script create a copy and terminate itself?

  - by ricedragon

  So far I used trap " call function" 2 fucntion { ./test.sh exit } but it never reaches the exit line and a whole bunch of process piles up any one got any idea? I tried & (bg) but i need to be able to keep doing it , the bg only allows me to do it once The point of it is when i type ctrl C it should terminate the original test.sh but it should also call itself before terminating hence create a new process.

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• Calling pthread_cond_signal without locking mutex

  - by Maysam

  Hi, I read somewhere that we should lock the mutex before calling pthread_cond_signal and unlock the mutext after calling it: The pthread_cond_signal() routine is used to signal (or wake up) another thread which is waiting on the condition variable. It should be called after mutex is locked, and must unlock mutex in order for pthread_cond_wait() routine to complete. My question is: isn't it OK to call pthread_cond_signal or pthread_cond_broadcast methods without locking the mutex?

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• Program received signal from GDB: EXC_BAD_ACCESS

  - by user577185

  Well, I'm starting development on the Mac OS X this code that you'll see is in a book that I bought, really basic like Chapter 3. And I can't run it. PLEASE HELP ME: C301.m : #import <Foundation/Foundation.h> int main (int argc, const char * argv[]) { if (argc == 1) { NSLog (@"You need to provide a file name"); return -1; } FILE *wordFile = fopen("tmp/words.txt", "r"); char word[100]; while (fgets(word, 100, wordFile)) { word[strlen(word) - 1] = '\0'; NSLog(@"%s is %d characters long", word, strlen(word)); } fclose(wordFile); return 0; } //main The file is in its place. Thank you so much!

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• Erlang Linux signal handling

  - by jldupont

  Is it possible to trap Linux signals (e.g. SIGUSR1) through an handler in Erlang? (without having to resort to a driver crafted in C)

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