尝试并行运行一堆linq查询时,我遇到了僵局。
我正在使用此方法运行QTableView
:
import sys
import os
sys.path.append(os.environ.get('PS_SITEPACKAGES'))
from Qt import QtGui, QtWidgets, QtCore
from functools import partial
class FilterProxy(QtCore.QSortFilterProxyModel):
def __init__(self, *args, **kwargs):
super(FilterProxy, self).__init__(*args, **kwargs)
self.filters_colums = set()
self.mText = ""
def setText(self, text):
self.mText = text
self.invalidateFilter()
def appendColumn(self, name):
self.filters_colums.add(name.lower())
self.invalidateFilter()
def removeColumn(self, name):
self.filters_colums.discard(name.lower())
self.invalidateFilter()
def filterAcceptsRow(self, source_row, source_parent):
if self.mText:
for i in range(self.sourceModel().columnCount()):
header = self.sourceModel().headerData(i, QtCore.Qt.Horizontal)
text = self.sourceModel().index(source_row, i).data()
if header in self.filters_colums and self.mText in text.lower():
return True
return False
return True
class QDictTableView(QtWidgets.QWidget):
def __init__(self, *args, **kwargs):
super(QDictTableView, self).__init__(*args, **kwargs)
self.resize(400,300)
# controls
self.ui_search_input = QtWidgets.QLineEdit()
self.ui_search_input.setPlaceholderText('Search...')
self.ui_item_table = QtWidgets.QTableView()
self.ui_item_table.setEditTriggers(QtWidgets.QAbstractItemView.NoEditTriggers)
self.ui_item_table.setSelectionBehavior(QtWidgets.QAbstractItemView.SelectRows)
self.ui_item_table.verticalHeader().hide()
lay_filters = QtWidgets.QHBoxLayout()
lay_main = QtWidgets.QVBoxLayout(self)
lay_main.setAlignment(QtCore.Qt.AlignTop)
lay_main.addWidget(self.ui_search_input)
lay_main.addLayout(lay_filters)
lay_main.addWidget(self.ui_item_table)
model = self.populate_table()
self.proxy = FilterProxy()
self.proxy.setSourceModel(model)
self.ui_item_table.setModel(self.proxy)
for text in ("Name", "Age", "Career"):
checkbox = QtWidgets.QCheckBox(text)
checkbox.stateChanged.connect(partial(self.update_columns, text))
checkbox.setChecked(True)
lay_filters.addWidget(checkbox)
self.ui_search_input.textChanged.connect(self.proxy.setText)
def update_columns(self, text, state):
cols = self.ui_item_table.model().columnCount()
i = [self.ui_item_table.model().headerData(i, QtCore.Qt.Horizontal) for i in range(cols)].index(text.lower())
self.ui_item_table.setColumnHidden(i, state == QtCore.Qt.Unchecked)
if state == QtCore.Qt.Unchecked:
self.proxy.removeColumn(text)
else:
self.proxy.appendColumn(text)
def populate_table(self):
peoples = [
{'name': 'Kevin', 'age': 5, 'career': 'athlete'},
{'name': 'Maggie', 'age': 13, 'career': 'banker'},
{'name': 'Leslie', 'age': 32, 'career': 'banker'},
{'name': 'Emily', 'age': 45, 'career': 'athlete'},
{'name': 'David', 'age': 27, 'career': 'banker'},
{'name': 'Marie', 'age': 63, 'career': 'secretary'}
]
model = QtGui.QStandardItemModel()
headers = ["name", "age", "career"]
model.setHorizontalHeaderLabels(headers)
for row, people in enumerate(peoples):
items = []
for key, value in people.items():
col = headers.index(key)
item = QtGui.QStandardItem(str(value))
items.append(item)
model.insertRow(row, items)
return model
if __name__ == '__main__':
app = QtWidgets.QApplication(sys.argv)
ex = QDictTableView()
ex.show()
sys.exit(app.exec_())
我得到一个Task.WhenAll()
public async Task<MetabuildScan> GetLatestMetabuildScanAsync(string buildId)
{
var metabuildScanStatuses = new[] { "Completed", "Referenced" };
// Get the latest metabuild scan for this image build
var latestScan = await (from scan in _qsaContext.MetabuildScans
where scan.SoftwareImageBuildId == buildId
&& metabuildScanStatuses.Contains(scan.SIScanStatus)
orderby scan.SIScanStartedOn descending
select scan).FirstOrDefaultAsync();
// If there is a related scan, then use that one, else, use the one we just got
var latestCompletedScanId = latestScan?.RelatedScanId ?? latestScan?.Id;
return await _qsaContext.MetabuildScans
.FirstOrDefaultAsync(scan => scan.Id == latestCompletedScanId);
}
是使用Entity-Framework Core创建的。
起初,我以为System.InvalidOperationException: A second operation started on this context before a previous operation completed. Any instance members are not guaranteed to be thread safe.
可以解决我的问题(起初我有一个非异步的_qsaContext
),但是没有。
我想知道解决这个僵局的最佳解决方案是什么。我从中选择的表是一个大表,因此我无法将整个表拉入内存。
答案 0 :(得分:0)
与往常一样,将查询包裹在try / catch中,然后重复您的交易。
答案 1 :(得分:0)
实体框架DbContext不是线程安全的。您不能像尝试那样对它运行并行查询。
如果您需要一个共享的查询上下文,则需要逐个顺序地等待每个查询。
如果它们不需要共享的上下文,但是需要并行运行,则每个查询都需要有一个单独的上下文。
如果使用DI框架,也许您可以研究使DbContext成为瞬态对象(而不是我假设的是Scoped对象),并将其注入到将调用您的查询方法的查询类中。