objective-c – 使用Grand Central Dispatch进行文件监控

概述我使用 David Hamrick的代码示例来使用GCD监视文件. int fildes = open("/path/to/config.plist", O_RDONLY);dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);dispatch_source_t sourc 我使用 David Hamrick的代码示例来使用GCD监视文件.

int fildes = open("/path/to/config.pList",O_RDONLY);dispatch_queue_t queue = dispatch_get_global_queue(disPATCH_QUEUE_PRIORITY_DEFAulT,0);dispatch_source_t source = dispatch_source_create(disPATCH_SOURCE_TYPE_VNODE,fildes,disPATCH_VNODE_DELETE | disPATCH_VNODE_WRITE | disPATCH_VNODE_EXTEND | disPATCH_VNODE_ATTRIB | disPATCH_VNODE_link | disPATCH_VNODE_REname | disPATCH_VNODE_REVOKE,queue);dispatch_source_set_event_handler(source,^{    //Reload the config file});dispatch_source_set_cancel_handler(source,^{    //Handle the cancel});dispatch_resume(source);

我想用来监视一个pList的变化.我在第一次更改后收到通知,但没有收到以下更改.为什么？

解决方法 您确实可以在收到disPATCH_VNODE_DELETE时重新打开文件并重新注册源(删除前一个).或者您可以使用专为此类场景设计的调用,即dispatch_io_create_with_path() – 它不仅会按路径观看,还会为您打开文件并让您以异步方式读取内容.

既然你问(不知道你要求哪种技术,但这里最简单)这里有一个独立的代码示例：

#include <dispatch/dispatch.h>#include <stdio.h>int main(int ac,char *av[]){  int fdes = open("/tmp/pleasewatchthis",O_RDONLY);  dispatch_queue_t queue = dispatch_get_global_queue(0,0);  voID (^eventHandler)(voID),(^cancelHandler)(voID);  unsigned long mask = disPATCH_VNODE_DELETE | disPATCH_VNODE_WRITE | disPATCH_VNODE_EXTEND | disPATCH_VNODE_ATTRIB | disPATCH_VNODE_link | disPATCH_VNODE_REname | disPATCH_VNODE_REVOKE;  __block dispatch_source_t source;  eventHandler = ^{    unsigned long l = dispatch_source_get_data(source);    if (l & disPATCH_VNODE_DELETE) {      printf("watched file deleted!  cancelling source\n");      dispatch_source_cancel(source);    }    else {      // handle the file has data case      printf("watched file has data\n");    }  };  cancelHandler = ^{    int fdes = dispatch_source_get_handle(source);    close(fdes);    // Wait for new file to exist.    while ((fdes = open("/tmp/pleasewatchthis",O_RDONLY)) == -1)      sleep(1);    printf("re-opened target file in cancel handler\n");    source = dispatch_source_create(disPATCH_SOURCE_TYPE_VNODE,fdes,mask,queue);    dispatch_source_set_event_handler(source,eventHandler);    dispatch_source_set_cancel_handler(source,cancelHandler);    dispatch_resume(source);  };  source = dispatch_source_create(disPATCH_SOURCE_TYPE_VNODE,queue);  dispatch_source_set_event_handler(source,eventHandler);  dispatch_source_set_cancel_handler(source,cancelHandler);  dispatch_resume(source);  dispatch_main();}

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