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Golang for select loop consumes 100% of cpu

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-1

I have a resource that needs to be loaded before any access is allowed to it. It also needs to be updated every minute.

The channels are of length 1 struct, so the loop will be blocked if the resource has not been loaded.

This code below started to use 100% of my cpu, I tried adding

time.Sleep(10 * time.Millisecond)

Which made the application cpu consumption drop to 1%

I am thinking a ticker would be a better option for the timed collection.

Any ideas why it would consume 100% cpu or any better ideas for implemention?

func (al *AsyncLoop) Run() 
 go func() 
 for 
 select 
 case <-al.chanFetchRequest:
 if al.fetched == false 
 al.fetchData()
 else if al.lastUpdated.Add(1*time.Minute).Unix() < time.Now().Unix() && al.fetching == false 
 go al.fetchData()
 
 al.chanFetchResponse <- struct
 continue
 default:
 continue
 
 
 ()

go cpu

share|improve this question

edited Mar 26 at 23:09

Charles Bryant

asked Mar 26 at 22:43

Charles BryantCharles Bryant

43311 gold badge77 silver badges1818 bronze badges

• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  You have a default case in your select, meaning that the for loop will spin if there is nothing to read from al.al.chanFetchRequest.
  
  – Tim Cooper
  Mar 26 at 22:46
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Also looking at how al.lastUpdated, scp.fetching and go al.fetchData() there is also a chance you have data race in this code as well.
  
  – zerkms
  Mar 26 at 22:59
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes thanks for spotting that, I will add some get and set methods with a mutex
  
  – Charles Bryant
  Mar 26 at 23:25
  

  
  
  
  

add a comment | 

-1

I have a resource that needs to be loaded before any access is allowed to it. It also needs to be updated every minute.

The channels are of length 1 struct, so the loop will be blocked if the resource has not been loaded.

This code below started to use 100% of my cpu, I tried adding

time.Sleep(10 * time.Millisecond)

Which made the application cpu consumption drop to 1%

I am thinking a ticker would be a better option for the timed collection.

Any ideas why it would consume 100% cpu or any better ideas for implemention?

func (al *AsyncLoop) Run() 
 go func() 
 for 
 select 
 case <-al.chanFetchRequest:
 if al.fetched == false 
 al.fetchData()
 else if al.lastUpdated.Add(1*time.Minute).Unix() < time.Now().Unix() && al.fetching == false 
 go al.fetchData()
 
 al.chanFetchResponse <- struct
 continue
 default:
 continue
 
 
 ()

go cpu

share|improve this question

edited Mar 26 at 23:09

Charles Bryant

asked Mar 26 at 22:43

Charles BryantCharles Bryant

43311 gold badge77 silver badges1818 bronze badges

• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  You have a default case in your select, meaning that the for loop will spin if there is nothing to read from al.al.chanFetchRequest.
  
  – Tim Cooper
  Mar 26 at 22:46
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Also looking at how al.lastUpdated, scp.fetching and go al.fetchData() there is also a chance you have data race in this code as well.
  
  – zerkms
  Mar 26 at 22:59
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes thanks for spotting that, I will add some get and set methods with a mutex
  
  – Charles Bryant
  Mar 26 at 23:25
  

  
  
  
  

add a comment | 

I have a resource that needs to be loaded before any access is allowed to it. It also needs to be updated every minute.

The channels are of length 1 struct, so the loop will be blocked if the resource has not been loaded.

This code below started to use 100% of my cpu, I tried adding

time.Sleep(10 * time.Millisecond)

Which made the application cpu consumption drop to 1%

I am thinking a ticker would be a better option for the timed collection.

Any ideas why it would consume 100% cpu or any better ideas for implemention?

func (al *AsyncLoop) Run() 
 go func() 
 for 
 select 
 case <-al.chanFetchRequest:
 if al.fetched == false 
 al.fetchData()
 else if al.lastUpdated.Add(1*time.Minute).Unix() < time.Now().Unix() && al.fetching == false 
 go al.fetchData()
 
 al.chanFetchResponse <- struct
 continue
 default:
 continue
 
 
 ()

go cpu

share|improve this question

edited Mar 26 at 23:09

Charles Bryant

asked Mar 26 at 22:43

Charles BryantCharles Bryant

43311 gold badge77 silver badges1818 bronze badges

time.Sleep(10 * time.Millisecond)

func (al *AsyncLoop) Run() 
 go func() 
 for 
 select 
 case <-al.chanFetchRequest:
 if al.fetched == false 
 al.fetchData()
 else if al.lastUpdated.Add(1*time.Minute).Unix() < time.Now().Unix() && al.fetching == false 
 go al.fetchData()
 
 al.chanFetchResponse <- struct
 continue
 default:
 continue
 
 
 ()

share|improve this question

edited Mar 26 at 23:09

Charles Bryant

asked Mar 26 at 22:43

Charles BryantCharles Bryant

43311 gold badge77 silver badges1818 bronze badges

share|improve this question

edited Mar 26 at 23:09

Charles Bryant

asked Mar 26 at 22:43

Charles BryantCharles Bryant

43311 gold badge77 silver badges1818 bronze badges

asked Mar 26 at 22:43

Charles BryantCharles Bryant

43311 gold badge77 silver badges1818 bronze badges

asked Mar 26 at 22:43

Charles BryantCharles Bryant

43311 gold badge77 silver badges1818 bronze badges

1 Answer
1

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0

I think you just post to al.chanFetchRequest when there is new data so I think you have to keep reading from this channel all the time. Adding a ticker to the select might cause you to fetch the data even if it has not changed or (worse) before it has even loaded. Why not, in the normal case, take the time whenever you fetch the data then the next time make sure you have waited enough time before fetching again. Something like this:

 var nextFetch time.Time
 for 
 select 
 case <-al.chanFetchRequest:
 if al.fetched == false 
 al.fetchData()
 nextFetch = time.Now().Add(1 * time.Minute)
 else if time.Now().After(nextFetch) 
 al.fetchData()
 nextFetch = time.Now().Add(1 * time.Minute)
 
 al.chanFetchResponse <- struct
 
 

share|improve this answer

edited Mar 26 at 23:14

answered Mar 26 at 23:07

AJRAJR

1381010 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  A select with a single case has no purpose. Just read from the channel.
  
  – Adrian
  Mar 27 at 14:06
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Adrian thanks - you are right which is exactly what I said in my 2nd answer (below). However, it could be useful if you think you will add other cases later.
  
  – AJR
  Mar 29 at 7:06
  

  
  
  
  

add a comment | 

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0

I think you just post to al.chanFetchRequest when there is new data so I think you have to keep reading from this channel all the time. Adding a ticker to the select might cause you to fetch the data even if it has not changed or (worse) before it has even loaded. Why not, in the normal case, take the time whenever you fetch the data then the next time make sure you have waited enough time before fetching again. Something like this:

 var nextFetch time.Time
 for 
 select 
 case <-al.chanFetchRequest:
 if al.fetched == false 
 al.fetchData()
 nextFetch = time.Now().Add(1 * time.Minute)
 else if time.Now().After(nextFetch) 
 al.fetchData()
 nextFetch = time.Now().Add(1 * time.Minute)
 
 al.chanFetchResponse <- struct
 
 

share|improve this answer

edited Mar 26 at 23:14

answered Mar 26 at 23:07

AJRAJR

1381010 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  A select with a single case has no purpose. Just read from the channel.
  
  – Adrian
  Mar 27 at 14:06
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Adrian thanks - you are right which is exactly what I said in my 2nd answer (below). However, it could be useful if you think you will add other cases later.
  
  – AJR
  Mar 29 at 7:06
  

  
  
  
  

add a comment | 

0

I think you just post to al.chanFetchRequest when there is new data so I think you have to keep reading from this channel all the time. Adding a ticker to the select might cause you to fetch the data even if it has not changed or (worse) before it has even loaded. Why not, in the normal case, take the time whenever you fetch the data then the next time make sure you have waited enough time before fetching again. Something like this:

 var nextFetch time.Time
 for 
 select 
 case <-al.chanFetchRequest:
 if al.fetched == false 
 al.fetchData()
 nextFetch = time.Now().Add(1 * time.Minute)
 else if time.Now().After(nextFetch) 
 al.fetchData()
 nextFetch = time.Now().Add(1 * time.Minute)
 
 al.chanFetchResponse <- struct
 
 

share|improve this answer

edited Mar 26 at 23:14

answered Mar 26 at 23:07

AJRAJR

1381010 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  A select with a single case has no purpose. Just read from the channel.
  
  – Adrian
  Mar 27 at 14:06
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Adrian thanks - you are right which is exactly what I said in my 2nd answer (below). However, it could be useful if you think you will add other cases later.
  
  – AJR
  Mar 29 at 7:06
  

  
  
  
  

add a comment | 

I think you just post to al.chanFetchRequest when there is new data so I think you have to keep reading from this channel all the time. Adding a ticker to the select might cause you to fetch the data even if it has not changed or (worse) before it has even loaded. Why not, in the normal case, take the time whenever you fetch the data then the next time make sure you have waited enough time before fetching again. Something like this:

 var nextFetch time.Time
 for 
 select 
 case <-al.chanFetchRequest:
 if al.fetched == false 
 al.fetchData()
 nextFetch = time.Now().Add(1 * time.Minute)
 else if time.Now().After(nextFetch) 
 al.fetchData()
 nextFetch = time.Now().Add(1 * time.Minute)
 
 al.chanFetchResponse <- struct
 
 

share|improve this answer

edited Mar 26 at 23:14

answered Mar 26 at 23:07

AJRAJR

1381010 bronze badges

 var nextFetch time.Time
 for 
 select 
 case <-al.chanFetchRequest:
 if al.fetched == false 
 al.fetchData()
 nextFetch = time.Now().Add(1 * time.Minute)
 else if time.Now().After(nextFetch) 
 al.fetchData()
 nextFetch = time.Now().Add(1 * time.Minute)
 
 al.chanFetchResponse <- struct
 
 

share|improve this answer

edited Mar 26 at 23:14

answered Mar 26 at 23:07

AJRAJR

1381010 bronze badges

answered Mar 26 at 23:07

AJRAJR

1381010 bronze badges

answered Mar 26 at 23:07

AJRAJR

1381010 bronze badges