I noticed that Web Content process crashes are sometimes followed by this being logged: Unable to acquire assertion for process 0 This happens because the ProcessAssertion constructor gets called with a 0 pid, which comes from the connection to the crashed process, which is no longer valid. In this backtrace: #0 0x0000000195b0d300 in WebKit::ProcessAssertion::ProcessAssertion(int, WebKit::AssertionState, WTF::Function<void ()>&&) at WebKit2/UIProcess/ios/ProcessAssertionIOS.mm:167 #1 0x0000000195b0da40 in WebKit::ProcessAndUIAssertion::ProcessAndUIAssertion(int, WebKit::AssertionState) at WebKit2/UIProcess/ios/ProcessAssertionIOS.mm:228 #2 0x0000000195a83f34 in std::__1::__unique_if<WebKit::ProcessAndUIAssertion>::__unique_single std::__1::make_unique<WebKit::ProcessAndUIAssertion, int, WebKit::AssertionState>(int&&, WebKit::AssertionState&&) [inlined] at /usr/bin/../include/c++/v1/memory:3153 #3 0x0000000195a83f18 in IPC::ConnectionTerminationWatchdog::ConnectionTerminationWatchdog(WTF::OSObjectPtr<NSObject<OS_xpc_object>*>&, double) at WebKit2/Platform/IPC/mac/ConnectionMac.mm:93 #4 0x0000000195a82ff0 in IPC::ConnectionTerminationWatchdog::ConnectionTerminationWatchdog(WTF::OSObjectPtr<NSObject<OS_xpc_object>*>&, double) [inlined] at WebKit2/Platform/IPC/mac/ConnectionMac.mm:95 #5 0x0000000195a82fe4 in IPC::ConnectionTerminationWatchdog::createConnectionTerminationWatchdog(WTF::OSObjectPtr<NSObject<OS_xpc_object>*>&, double) at WebKit2/Platform/IPC/mac/ConnectionMac.mm:85 #6 0x0000000195a7c2c0 in WebKit::ChildProcessProxy::shutDownProcess() at WebKit2/UIProcess/ChildProcessProxy.cpp:196 #7 0x0000000195c52298 in WebKit::WebProcessProxy::shutDown() at WebKit2/UIProcess/WebProcessProxy.cpp:165 #8 0x0000000195c53dd4 in WebKit::WebProcessProxy::didClose(IPC::Connection&) at WebKit2/UIProcess/WebProcessProxy.cpp:523 shutDownProcess() should not call Connection::terminateSoon if the connection is already invalid.
<rdar://problem/29778802>