<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">Yes, NULL buffers are valid - they aren’t an MPI object. There is no prohibition about passing them; only if they are used to form an invalid address (note that a datatype with absolute addresses relies on NULL as the buffer address).<div><br></div><div>Bill</div><div><br><div>
William Gropp<br>Director, Parallel Computing Institute<br>Thomas M. Siebel Chair in Computer Science<br>Chief Scientist, NCSA<br>University of Illinois Urbana-Champaign<br><br><br><br><br>
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<br><div><div>On Jan 12, 2016, at 9:49 PM, Jeff Hammond <<a href="mailto:jeff.science@gmail.com">jeff.science@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><font size="2"><span style="background-color:rgba(255,255,255,0)">Who wrote Example 4.23 of MPI 3.1?</span></font><div><font size="2"><br></font></div><div><font size="2">I propose to add the exception rather than delete that example. I do not want to have to use real datatypes when sending nothing. </font></div><div><font size="2"><br></font></div><div><font size="2"><span style="-webkit-tap-highlight-color: rgba(26, 26, 26, 0.301961);">Is NULL a valid <span></span>buffer handle? Can I pass null pointers when count=0?<br></span><span style="background-color:rgba(255,255,255,0)"></span></font><div><font size="2"><br></font></div><div><font size="2"><span style="-webkit-tap-highlight-color: rgba(26, 26, 26, 0.301961);">Jeff <br></span><span style="background-color:rgba(255,255,255,0)"></span></font><div><br>On Tuesday, January 12, 2016, William Gropp <<a href="mailto:wgropp@illinois.edu">wgropp@illinois.edu</a>> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word">The standard says that the null handles are invalid for input unless explicitly permitted. There’s no exemption for a datatype argument where the associated count is zero.<div><br></div><div>Bill</div><div><br><div>
William Gropp<br>Director, Parallel Computing Institute<br>Thomas M. Siebel Chair in Computer Science<br>Chief Scientist, NCSA<br>University of Illinois Urbana-Champaign<br><br><br><br><br>
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<br><div><div>On Jan 12, 2016, at 9:26 PM, Jeff Hammond <<a href="javascript:_e(%7B%7D,'cvml','jeff.science@gmail.com');" target="_blank">jeff.science@gmail.com</a>> wrote:</div><br><blockquote type="cite"><div dir="ltr">Is it allowed to communicate messages with (buffer=NULL,count=0,type=MPI_DATATYPE_NULL)?<div><br></div><div>George thinks MPI_DATATYPE_NULL cannot be used even when count=0, which I think is ridiculous, particularly when one makes the analogy to buffer=NULL.</div><div><br></div><div>See <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__www.open-2Dmpi.org_community_lists_users_2016_01_28255.php&d=BQMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=195OD1c98cxYlIPBUDzl00KueizThEKs34a9DvL37eY&m=tWmZZT774xAE-RjUpTuHeZ0-hHkwEoE5sQADPmobarg&s=7rkfIDjMiCphV1WD00EIRKeH44dIa97JAz6C3HTPF7M&e=" target="_blank">http://www.open-mpi.org/community/lists/users/2016/01/28255.php</a> for the thread in question.</div><div><br></div><div>There is example code in MPI that uses this behavior. George and I agree that example text is non-normative, but I cannot imagine how this example came to exist without the Forum believing it to be valid.</div><div><br>Jeff<br clear="all"><div><br></div>-- <br><div>Jeff Hammond<br><a href="javascript:_e(%7B%7D,'cvml','jeff.science@gmail.com');" target="_blank">jeff.science@gmail.com</a><br><a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__jeffhammond.github.io_&d=BQMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=195OD1c98cxYlIPBUDzl00KueizThEKs34a9DvL37eY&m=tWmZZT774xAE-RjUpTuHeZ0-hHkwEoE5sQADPmobarg&s=l_bf2ha5FZxeiaQWAM3hSLdzVFrXjR7lP6X99U3j8Yo&e=" target="_blank">http://jeffhammond.github.io/</a></div>
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