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体验新版 GitCode,发现更多精彩内容 >>
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0fa17ff5
编写于
2月 01, 2011
作者:
E
Eric Blake
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差异文件
docs: more on qemu locking patterns
* src/qemu/THREADS.txt: Improve documentation.
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0b864eb1
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77 addition
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23 deletion
+77
-23
src/qemu/THREADS.txt
src/qemu/THREADS.txt
+77
-23
未找到文件。
src/qemu/THREADS.txt
浏览文件 @
0fa17ff5
...
...
@@ -4,7 +4,7 @@
This document describes how thread safety is ensured throughout
the QEMU driver. The criteria for this model are:
- Objects must never be exclusively locked for any pro
-
longed time
- Objects must never be exclusively locked for any prolonged time
- Code which sleeps must be able to time out after suitable period
- Must be safe against dispatch asynchronous events from monitor
...
...
@@ -36,11 +36,11 @@ There are a number of locks on various objects
Once the lock is held, you must *NOT* try to lock the driver. You must
release all virDomainObjPtr locks before locking the driver, or deadlock
*WILL* occur
r
.
*WILL* occur.
If the lock needs to be dropped & then re-acquired for a short period of
time, the reference count must be incremented first using virDomainObjRef().
If the reference count is incremented in this way, it is not nec
c
essary
If the reference count is incremented in this way, it is not necessary
to have the driver locked when re-acquiring the dropped locked, since the
reference count prevents it being freed by another thread.
...
...
@@ -51,15 +51,20 @@ There are a number of locks on various objects
* qemuMonitorPrivatePtr: Job condition
Since virDomainObjPtr lock must not be held during sleeps, the job
condition
provides additional protection for code making updates.
Since virDomainObjPtr lock must not be held during sleeps, the job
condition
provides additional protection for code making updates.
Immediately after acquiring the virDomainObjPtr lock, any method which intends
to update state, must acquire the job condition. The virDomainObjPtr lock
is released while blocking on this condition variable. Once the job condition
is acquired a method can safely release the virDomainObjPtr lock whenever it
hits a piece of code which may sleep/wait, and re-acquire it after the sleep/
wait.
Immediately after acquiring the virDomainObjPtr lock, any method
which intends to update state must acquire the job condition. The
virDomainObjPtr lock is released while blocking on this condition
variable. Once the job condition is acquired, a method can safely
release the virDomainObjPtr lock whenever it hits a piece of code
which may sleep/wait, and re-acquire it after the sleep/wait.
Since the virDomainObjPtr lock was dropped while waiting for the
job condition, it is possible that the domain is no longer active
when the condition is finally obtained. The monitor lock is only
safe to grab after verifying that the domain is still active.
* qemuMonitorPtr: Mutex
...
...
@@ -110,13 +115,15 @@ To acquire the job mutex
qemuDomainObjBeginJob() (if driver is unlocked)
- Increments ref count on virDomainObjPtr
- Wait qemuDomainObjPrivate condition 'jobActive != 0' using virDomainObjPtr mutex
- Wait qemuDomainObjPrivate condition 'jobActive != 0' using
virDomainObjPtr mutex
- Sets jobActive to 1
qemuDomainObjBeginJobWithDriver() (if driver needs to be locked)
- Unlocks driver
- Increments ref count on virDomainObjPtr
- Wait qemuDomainObjPrivate condition 'jobActive != 0' using virDomainObjPtr mutex
- Wait qemuDomainObjPrivate condition 'jobActive != 0' using
virDomainObjPtr mutex
- Sets jobActive to 1
- Unlocks virDomainObjPtr
- Locks driver
...
...
@@ -140,10 +147,10 @@ To acquire the QEMU monitor lock
- Releases the virDomainObjPtr lock
qemuDomainObjExitMonitor()
- Acquires the virDomainObjPtr lock
- Releases the qemuMonitorObjPtr lock
- Acquires the virDomainObjPtr lock
NB: caller must take care to drop the driver lock if nec
c
essary
NB: caller must take care to drop the driver lock if necessary
To acquire the QEMU monitor lock with the driver lock held
...
...
@@ -154,11 +161,25 @@ To acquire the QEMU monitor lock with the driver lock held
- Releases the driver lock
qemuDomainObjExitMonitorWithDriver()
- Releases the qemuMonitorObjPtr lock
- Acquires the driver lock
- Acquires the virDomainObjPtr lock
- Releases the qemuMonitorObjPtr lock
NB: caller must take care to drop the driver lock if neccessary
NB: caller must take care to drop the driver lock if necessary
To keep a domain alive while waiting on a remote command, starting
with the driver lock held
qemuDomainObjEnterRemoterWithDriver()
- Increments ref count on virDomainObjPtr
- Releases the virDomainObjPtr lock
- Releases the driver lock
qemuDomainObjExitRemoteWithDriver()
- Acquires the driver lock
- Acquires the virDomainObjPtr lock
- Decrements ref count on virDomainObjPtr
Design patterns
...
...
@@ -236,9 +257,11 @@ Design patterns
...do prep work...
qemuDomainObjEnterMonitor(obj);
qemuMonitorXXXX(priv->mon);
qemuDomainObjExitMonitor(obj);
if (virDomainObjIsActive(vm)) {
qemuDomainObjEnterMonitor(obj);
qemuMonitorXXXX(priv->mon);
qemuDomainObjExitMonitor(obj);
}
...do final work...
...
...
@@ -261,9 +284,11 @@ Design patterns
...do prep work...
qemuDomainObjEnterMonitorWithDriver(driver, obj);
qemuMonitorXXXX(priv->mon);
qemuDomainObjExitMonitorWithDriver(driver, obj);
if (virDomainObjIsActive(vm)) {
qemuDomainObjEnterMonitorWithDriver(driver, obj);
qemuMonitorXXXX(priv->mon);
qemuDomainObjExitMonitorWithDriver(driver, obj);
}
...do final work...
...
...
@@ -272,6 +297,35 @@ Design patterns
qemuDriverUnlock(driver);
* Coordinating with a remote server for migraion
virDomainObjPtr obj;
qemuDomainObjPrivatePtr priv;
qemuDriverLock(driver);
obj = virDomainFindByUUID(driver->domains, dom->uuid);
qemuDomainObjBeginJobWithDriver(obj);
...do prep work...
if (virDomainObjIsActive(vm)) {
qemuDomainObjEnterRemoteWithDriver(driver, obj);
...communicate with remote...
qemuDomainObjExitRemoteWithDriver(driver, obj);
/* domain may have been stopped while we were talking to remote */
if (!virDomainObjIsActive(vm)) {
qemuReportError(VIR_ERR_INTERNAL_ERROR, "%s",
_("guest unexpectedly quit"));
}
}
...do final work...
qemuDomainObjEndJob(obj);
virDomainObjUnlock(obj);
qemuDriverUnlock(driver);
Summary
-------
...
...
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