记录最近遇到的一个奇葩的crash：
现象：
UIWebView在首次被调用，如
[
UIWebView class]
时，如果在非主线程，会导致crash。
原因：
UIWebView使用了类似懒加载的机制，第一次调用时会进行部分初始化，该部分初始化需要在主线程进行。
解决方案：
在主线程调用一把[UIWebView class]，之后就可以在任意线程进行UIWebView相关操作了。
po时抛出的错误：
error: Execution was interrupted, reason: EXC_BREAKPOINT (code=EXC_I386_BPT, subcode=
0x0).
The
process has been returned
to the state
before expression evaluation.
crash堆栈
WebCore`WebCore::FloatingPointEnvironment::saveMainThreadEnvironment:
0x121f623d0
<+0>: pushq %rbp
0x121f623d1
<+1>: movq %rsp, %rbp
0x121f623d4
<+4>: pushq %rbx
0x121f623d5
<+5>: pushq %rax
0x121f623d6
<+6>: movq %rdi, %rbx
0x121f623d9
<+9>: cmpb $0x0, 0x10(%rbx)
0x121f623dd
<+13>: jne 0x121f623fb ;
<+43>
0x121f623df
<+15>: callq 0x122df09b0 ; symbol stub for: WTF::isUIThread()
0x121f623e4
<+20>: testb %al, %al
0x121f623e6
<+22>: je 0x121f623fc ;
<+44>
0x121f623e8
<+24>: movq %rbx, %rdi
0x121f623eb
<+27>: callq 0x122df1a12 ; symbol stub for: fegetenv
0x121f623f0
<+32>: movb $0x1, 0x10(%rbx)
0x121f623f4
<+36>: addq $0x8, %rsp
0x121f623f8
<+40>: popq %rbx
0x121f623f9
<+41>: popq %rbp
0x121f623fa
<+42>: retq
0x121f623fb
<+43>: int3
0x121f623fc
<+44>: int3
-> 0x121f623fd
<+45>: nopl (%rax)
WebCore`WebCore::FloatPoint::FloatPoint:
0x121f62430
<+0>: pushq %rbp
0x121f62431
<+1>: movq %rsp, %rbp
-> 0x121f62434
<+4>: cvtsi2ssl (%rsi), %xmm0
0x121f62438
<+8>: movss %xmm0, (%rdi)
0x121f6243c
<+12>: xorps %xmm0, %xmm0
0x121f6243f
<+15>: cvtsi2ssl 0x4(%rsi), %xmm0
0x121f62444
<+20>: movss %xmm0, 0x4(%rdi)
0x121f62449
<+25>: popq %rbp
0x121f6244a
<+26>: retq
0x121f6244b
<+27>: nopl (%rax,%rax)
