I'm using the code example by David Hamrick to monitor a file using GCD.
我正在使用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);
I want to use to monitor a change of a plist. I get a notification after the first change but not for the following changes. Why?
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?
2 个解决方案
#1
11
You can indeed just re-open the file and re-register a source (deleting the previous one) when DISPATCH_VNODE_DELETE is received. Or you can use a call which was devised for just this kind of scenario, namely dispatch_io_create_with_path() - that will not only watch by path, it will open the file for you and let you read the contents asynchronously.
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。
Since you asked (not sure which technique you asked for, but here's the simplest) here's a stand-alone code sample:
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,fdes, mask, queue);
dispatch_source_set_event_handler(source, eventHandler);
dispatch_source_set_cancel_handler(source, cancelHandler);
dispatch_resume(source);
dispatch_main();
}
#2
1
After a little bit a research I found out :
经过一番研究后我发现:
=> I was getting the flag DISPATCH_VNODE_DELETE
=>我收到了标志DISPATCH_VNODE_DELETE
I was monitoring ~/Library/Preferences/com.apple.dock.plist
As I found out, changing the dock orientation, deletes the original file and replaces it with a new one.
我在监视〜/ Library / Preferences / com.apple.dock.plist正如我所知,更改停靠方向,删除原始文件并用新文件替换它。
Therefore, the monitoring stopped.
因此,监控停止了。
The same author proposes a solution where in case of deletion, the GCD block call itself to continue the monitoring.
同一作者提出了一种解决方案,在删除的情况下,GCD块调用自身继续监视。
#1
11
You can indeed just re-open the file and re-register a source (deleting the previous one) when DISPATCH_VNODE_DELETE is received. Or you can use a call which was devised for just this kind of scenario, namely dispatch_io_create_with_path() - that will not only watch by path, it will open the file for you and let you read the contents asynchronously.
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。
Since you asked (not sure which technique you asked for, but here's the simplest) here's a stand-alone code sample:
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,fdes, mask, queue);
dispatch_source_set_event_handler(source, eventHandler);
dispatch_source_set_cancel_handler(source, cancelHandler);
dispatch_resume(source);
dispatch_main();
}
#2
1
After a little bit a research I found out :
经过一番研究后我发现:
=> I was getting the flag DISPATCH_VNODE_DELETE
=>我收到了标志DISPATCH_VNODE_DELETE
I was monitoring ~/Library/Preferences/com.apple.dock.plist
As I found out, changing the dock orientation, deletes the original file and replaces it with a new one.
我在监视〜/ Library / Preferences / com.apple.dock.plist正如我所知,更改停靠方向,删除原始文件并用新文件替换它。
Therefore, the monitoring stopped.
因此,监控停止了。
The same author proposes a solution where in case of deletion, the GCD block call itself to continue the monitoring.
同一作者提出了一种解决方案,在删除的情况下,GCD块调用自身继续监视。