Question

我是初学者，有一个简单的问题：

我有一个函数 myfunction（），每100毫秒定期调用一次。在这个函数中，我必须在 myfunction（）的beginn第一次调用时调用另一个函数，但是不能定期调用。

org.springframework.beans.factory.BeanDefinitionStoreException: Failed to process import candidates for configuration class [nl.insiteweb.acc.Application]; nested exception is java.lang.IllegalArgumentException: No auto configuration classes found in META-INF/spring.factories. If you are using a custom packaging, make sure that file is correct.
    at org.springframework.context.annotation.ConfigurationClassParser.processDeferredImportSelectors(ConfigurationClassParser.java:520) ~[testproject.jar:na]
    at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:184) ~[testproject.jar:na]
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(ConfigurationClassPostProcessor.java:308) ~[testproject.jar:na]
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(ConfigurationClassPostProcessor.java:228) ~[testproject.jar:na]
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:270) ~[testproject.jar:na]
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:93) ~[testproject.jar:na]
    at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:686) ~[testproject.jar:na]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:524) ~[testproject.jar:na]
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122) ~[testproject.jar:na]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:737) [testproject.jar:na]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:370) [testproject.jar:na]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:314) [testproject.jar:na]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1162) [testproject.jar:na]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1151) [testproject.jar:na]
    at nl.insiteweb.acc.Application.main(Application.java:16) [testproject.jar:na]
Caused by: java.lang.IllegalArgumentException: No auto configuration classes found in META-INF/spring.factories. If you are using a custom packaging, make sure that file is correct.
    at org.springframework.util.Assert.notEmpty(Assert.java:276) ~[testproject.jar:na]
    at org.springframework.boot.autoconfigure.AutoConfigurationImportSelector.getCandidateConfigurations(AutoConfigurationImportSelector.java:152) ~[testproject.jar:na]
    at org.springframework.boot.autoconfigure.AutoConfigurationImportSelector.selectImports(AutoConfigurationImportSelector.java:94) ~[testproject.jar:na]
    at org.springframework.context.annotation.ConfigurationClassParser.processDeferredImportSelectors(ConfigurationClassParser.java:512) ~[testproject.jar:na]
    ... 14 common frames omitted

如何在c中实现这一点？

Answer 1

使用static？

的内容

void myfunction() // function is called periodically every 100 ms
{
    static int once = 1;
    if (once) {
        mySubfunction(); 
        once = 0;
    }
}

示例中的变量once只会被初始化一次，并且由于static关键字而在调用之间保留其值。

请注意多线程环境中的含义，请参阅this question。

Answer 2

你可以拥有像

这样的东西

static int flag = 1
void myfunction() // function is called periodically every 100 ms
{
    if(flag)
    {
       mySubfunction(); 
       flag = 0;
    }     
 }

...

Answer 3

首先看看任务很简单，可以是下一个代码：

void func()
{
    static LONG first = TRUE;
    if (_InterlockedExchange(&first, FALSE))
    {
        subfunc();
    }
    // some code
}

这样可以100％保证subfunc()只会被调用一次，即使多个线程同时调用你的func()

但如果// some code取决于subfunc的结果会怎样？在这种情况下，任务变得非常微不足道。需要一些同步。这里已经依赖于os或编译器。在Windows中，从Vista开始了解此问题并添加功能InitOnceExecuteOnce - 阅读Using One-Time Initialization 如果您的subfunc() 中没有且 out 参数代码可以非常简单：

BOOL CALLBACK InitOnceCallback(PINIT_ONCE /*InitOnce*/, PVOID /*Parameter*/,PVOID* /*Context*/) { subfunc(); return TRUE; } void func() { static INIT_ONCE once = RTL_RUN_ONCE_INIT; if (InitOnceExecuteOnce(&once, InitOnceCallback, 0, 0)) { // somecode } // error init }

也有一些现代编译器可以纠正句柄静态一次初始化。说CL的最新版本。用它代码可以是下一个：

void func() { static char tag = (subfunc(), 0); // some code }

此处CL内部调用特殊函数（在 CRT 中实现）_Init_thread_header，_Init_thread_footer - 实现可以查看crt源代码 - {{1} }

Answer 4

这可能比您正在寻找的更高级，但您可以使用函数指针并更改调用哪个函数。

// Function declarations
void mySubfunction(void);
void myNormalfunction(void);

// Function pointer, which can be changed at run time.
static void (*myfunction)(void) = mySubfunction;

void mySubfunction(void)
{
    // Do the sub-function stuff.

    // Change the function pointer to the normal function.
    myfunction = myNormalfunction();

    // Do the normal function stuff (if necessary on the first call).
    myNormalfunction();
}

void myNormalfunction(void)
{
    // Etc.
}

int main(void)
{
    int x;
    for(x = 0; x < 3; x++)
    {
        // Call myfunction as you usually would.
        myfunction();
    }
    return 0;
}

如何在周期性函数调用中只调用一次子函数

4 个答案: