fix LibVirtPoolSync #159
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fix LibVirtPoolSync #159
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The code looks good, however I think we should understand why we are trying to unlock the same lock twice. Why and how is this happening? Then we can create a proper fix, this one looks like a workaround. Can you reproduce the issue? If so do you know what might be the cause of it? |
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I was able to reproduce issue #121 by patching diff --git a/libvirt/pool_sync.go b/libvirt/pool_sync.go
index 8c53ac05..6a6fe9c2 100644
--- a/libvirt/pool_sync.go
+++ b/libvirt/pool_sync.go
@@ -1,6 +1,7 @@
package libvirt
import (
+ "log"
"sync"
)
@@ -29,9 +30,11 @@ func (ps LibVirtPoolSync) AcquireLock(pool string) {
lock, exists := ps.PoolLocks[pool]
if !exists {
lock = new(sync.Mutex)
+ log.Printf("[DEBUG] acquire lock (1); pool: '%s', ps: %+v, lock: %+v\n", pool, ps, lock)
ps.PoolLocks[pool] = lock
}
+ log.Printf("[DEBUG] acquire lock (2); pool: '%s', ps: %+v, lock: %+v\n", pool, ps, lock)
lock.Lock()
}
@@ -45,5 +48,6 @@ func (ps LibVirtPoolSync) ReleaseLock(pool string) {
return
}
+ log.Printf("[DEBUG] release lock; pool: '%s', ps: %+v, lock: %+v\n", pool, ps, lock)
lock.Unlock()
}(Oddly, it won't fail without the 1st The Terraform file: provider "libvirt" {
uri = "qemu:///system"
}
resource "libvirt_cloudinit" "disk" {
name = "commoninit.iso"
local_hostname = "node"
pool = "home"
}
resource "libvirt_volume" "disk" {
name = "disk_${count.index}"
size = "40960"
pool = "home"
count = 1
}(I guess it's just important to have multiple volumes) The log shows the following: This raises the question as to why two separate mutexes for |
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After searching the web, I found this: golang/go#20060. I guess we're doing it wrong. I'll fix this. |
monstermunchkin
changed the title
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FYI: Perhaps we should run |
inercia
suggested changes
Aug 18, 2017
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I don't think this is the right approach to the problem. I would create a singleton instance (a global, static instance, initialized probably in a init() function) and use it as a gatekeeper to the pools. I find the idea of keeping another map with booleans slightly hackish...
| @@ -62,7 +62,11 @@ func (ci *defCloudInit) CreateAndUpload(virConn *libvirt.Connect) (string, error | |||
| } | |||
| defer pool.Free() | |||
|
|
|||
| PoolSync.AcquireLock(ci.PoolName) | |||
| for { | |||
| if PoolSync.AcquireLock(ci.PoolName) { | |||
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Looping until we get the lock doesn't seem a very elegant solution...
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Don't know how to avoid looping in this case. I added a time.Sleep(..) to make it more CPU-friendly ;)
libvirt/pool_sync.go
Outdated
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|
||
| return pool | ||
| return &pool |
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I would use a more go-ish syntax:
func NewLibVirtPoolSync() *LibVirtPoolSync {
return &LibVirtPoolSync{
PoolLocks: make(map[string]*sync.Mutex),
//...
}
}
added 2 commits
November 17, 2017 10:09
Declare methods of LibVirtPoolSync as pointers since otherwise the entire construct is ineffective. Callers of `AcquireLock` are now responsible for making sure that the mutex is locked. This will prevent the following errors: * fatal error: concurrent map writes * panic: sync: unlock of unlocked mutex This fixes #121. Signed-off-by: Thomas Hipp <[email protected]>
Change code structure, and sleep after trying (and failing) to acquire a lock. Signed-off-by: Thomas Hipp <[email protected]>
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Declare methods of LibVirtPoolSync as pointers since otherwise the
entire construct is ineffective. Callers of
AcquireLockare nowresponsible for making sure that the mutex is locked.
This will prevent the following errors:
* fatal error: concurrent map writes
* panic: sync: unlock of unlocked mutex
This fixes #121.
Signed-off-by: Thomas Hipp [email protected]